ISSN 1403-5227

LICENTIATAVHANDLING

ZOOLOGISKA

INSTITUTIONEN Stockholms Universitet S-106 91 Stockholm

 

 

 

   

Social dominance and personality in male fowl (Gallus gallus domesticus)

Författare: Anna Favati Ämne: Etologi Löpnummer: 2013:4

 

 

Arbetets  titel:  

 

Social  dominance  and  personality  in  

male  fowl  (Gallus  gallus  domesticus)    

 

 

 

 

Författarens  namn:  Anna  Favati  

 

Handledare:  Olof  Leimar  

 

Forskningsämne:  Etologi  

 

Granskningskommitté:  Charlie  Cornwallis,  Sven  Jakobsson,  Bodil  Elmhagen  

 

Datum  för  seminarium:  2013-­‐05-­‐13  

 

 

 

INDEX

ABSTRACT ............................................................................................................................... 1

INTRODUCTION ..................................................................................................................... 3

METHODS ................................................................................................................................ 6

PAPER I ................................................................................................................................................ 6 PAPER II ............................................................................................................................................... 9

RESULTS ................................................................................................................................ 10

PAPER I .............................................................................................................................................. 10 PAPER II ............................................................................................................................................. 11

DISCUSSION .......................................................................................................................... 13

CONCLUSION ........................................................................................................................ 17

ACKNOWLEDGEMENT ....................................................................................................... 17

REFERENCES ........................................................................................................................ 19

LIST OF PAPERS

This thesis is based on the following manuscripts, referred to by their roman numerals.

Paper I

Favati, A., Leimar, O., Radesäter, T. and Løvlie, H. Social ‘states’ and personality: Stability

in social status and individual characteristics explain consistency in behavioural responses.

Submitted manuscript

Paper II

Favati, A., Leimar, O. and Løvlie, H. Aggressiveness and exploration predicts social status in

male domestic fowl (Gallus gallus domesticus). Manuscript

  1  

 

 1              

Social dominance and personality in male fowl (Gallus gallus domesticus)

Anna Favati

Department of zoology, Stockholm university, SE-106 91 Stockholm, Sweden

ABSTRACT

Individuals in social species commonly form dominance relationships among each other, and

are often observed to differ in behaviour depending on their social status. However, whether

such behavioural differences are a consequence of dominance position, or also a cause to it,

remains unclear. In this thesis I therefore investigated two perspectives of the relationship

between social dominance and personality in the domestic fowl (Gallus gallus domesticus), a

social species that forms relatively stable dominance hierarchies. In paper I I investigated the

influence of social status on the expression and consistency of behaviours by experimentally

changing status between repeated personality assays. The level of vigilance, activity and

exploration changed with social status, while boldness and territorial crows appeared as

stable individual properties, independent of status. These results showed that social status

contribute to both variation and consistency in behavioural responses. Social status should

therefore be taken into account when investigating and interpreting variation in personality.

In paper II I showed that behaviour in a novel arena test and during encounter with an

opponent can predict social status, more specifically that fast exploration and aggressiveness

predicted a dominant social position. Together, these results highlight the dynamics of the

two-way relationship between social position and individual behaviour and indicate that

individual behaviour can both be a cause and a consequence of social status.

Kruijt  1964  

  2  

 

 

 

 

 

 

 

 

 

 

 

 3  

INTRODUCTION

The take-off point of this licentiate thesis is the notion that not all individuals of a group

behave the same. Individuals of group living species often form dominance relationship

among each other, characterised by repeated outcome in favour of one participant of dyadic

agonistic interactions (Chase 1980). Socially dominant individuals commonly enjoy

increased access to resources, such as mating partners, which typically results in higher

reproductive success (Andersson 1994). Beside differences in social behaviour, like who is

more aggressive or perform more mating behaviours (e.g. Korzan et al. 2006, McGhee and

Travis 2010), there are also a few examples of behavioural differences between dominant and

subordinate individuals in non-social contexts (e.g. Colleter and Brown 2011, Dahlbom et al.

2011, David et al. 2011). For example, explorative great tits (Parus major) outcompete less

explorative ones (Verbeek et al. 1996), and bold three-spined sticklebacks (Gasterosteus

aculeatus) are more aggressive than shyer individuals (Huntingford 1976). However, there

are also a couple of examples of negative correlations, and no correlations between

explorative behaviour or boldness and dominance (Gomez-Laplaza 2002). In the mountain

chickadee (Poecile gambeli) less explorative individuals have higher chances of becoming

dominant, and boldness does not differ between dominant and subordinate individuals (Fox et

al. 2009). Interestingly, variation in such behavioural differences as activity, exploration,

boldness and aggression has been demonstrated to be consistent across time and context

(Wilson et al. 1994, Dall et al. 2004, Sih et al. 2004b, Groothuis and Carere 2005). Consistent

individual differences in behaviour have been described in a large number of species in

multiple taxa (Gosling 2001), and have been referred to as ‘animal personality’ (Dall et al.

2004) or ‘temperaments’ (Reale et al. 2007). When multiple behavioural traits are correlated

across time or context, the term ‘behavioural syndromes’ (Sih et al. 2004a) is used, and when

focus lays on the relationship between behavioural consistency and stress responses, the

related concept of ‘coping styles’ is often applied (Koolhaas et al. 1999). By scoring

individuals in personality tests, they can be categorised along a continuous axis of specific

personality traits, like boldness or exploration, and an individual is then said to have a

'behavioural type' or 'personality type' (e.g. more or less explorative, Sih et al. 2004b). The

research field of animal personality is still young, although fast growing. Nevertheless, there

are still major gaps in the understanding of why there is personality variation, including

questions about the mechanisms behind stable behavioural responses and the evolution and

  4  

maintenance of behavioural polymorphism (Dingemanse and Wolf 2010, Reale et al. 2010).

Current ideas of how variation is maintained include negative frequency dependence (Dall et

al. 2004, Wolf and Weissing 2010), selection regimes that fluctuate over time (Dingemanse

and de Goede 2004), and various trade-offs, for example between survival and reproductive

success (Smith and Blumstein 2008), or between growth and mortality (Stamps 2007).

Behavioural consistency within the individual has been suggested to be maintained by

physiological limitations in plasticity (Sih et al. 2004b), or by stability in physiological or

environmental states that changes slower than behaviour, and that affects the costs and

benefits of the individual's actions (e.g. body size, territory size or stable social hierarchies;

Houston and McNamara 1999, Dall et al. 2004, Dingemanse and Wolf 2010, Luttbeg and Sih

2010, Wolf and Weissing 2010). To learn more about the significance and evolution of

animal personality, studies of both through survival and reproductive success of different

personality types are requested (Dingemanse and Reale 2005, Smith and Blumstein 2008).

Social dominance typically affects reproductive success positively (Andersson 1994), and as

mentioned above, often seem to correlate to various personality traits. It would therefore be

interesting to further study this relationship. Not least, we should also aim to investigate the

causality behind this relationship, to reveal possible fitness consequences of various

personality traits.

There are four partly nonexclusive scenarios that may describe the causality of the

relationship between individual behaviour and social status. First, behavioural response may

be a consequence of the current social position (Cornwallis and Birkhead 2008). If so, we

expect a change in dominance status to lead to a change in behavioural response. This would

also mean that social status may represent a state that gives rise to consistent differences in

behaviour (Dall et al. 2004). Nevertheless, there are very few studies that have

experimentally altered social status to study if a change in behavioural response follows (but

see Cornwallis and Birkhead 2008). Second, social status and behavioural responses may

share a common underlying cause such as stress reactivity (Øverli et al. 2007, Carere et al.

2010). In this case we expect behaviours to be correlated to social status, but showing less

plasticity when status is changed. Third, and not exclusive from the second, the personality

type may affect an individuals' possibility to obtain a dominant social position (e.g. Dahlbom

et al. 2011). In this case, we expect to predict future social status by means of behavioural

responses in non-social contexts. Phenotypic traits like body size or size of armaments

etcetera have traditionally been investigated in this scenario and have been shown to predict

 5  

social status (Andersson 1994, Berglund et al. 1996). The potential link between behaviour

and future status is on the other hand much less investigated and the role for behavioural

differences to influence establishment of status is still poorly explored (but see e.g. Øverli et

al. 2004, Korzan et al. 2006, Dahlbom et al. 2011). And last, there is the remaining possibility

that variation in behavioural responses or personality traits is uncorrelated to variation in

social status. In this case, we expect no difference in the behavioural responses between

dominant and subordinate individuals, and behaviours to be unaffected by changes in social

position. Revealing the causal relationship between behavioural differences and social status

is essential for further understanding of how variation in personality types affect fitness, and

ultimately for understanding of the evolution of personality types. Each scenario described

above has been examined to some extent, but there is a lack of studies exploring more than

one of the scenarios outlines above in the same animal model. In this thesis, I aim to study the

causality of the relationship between behaviour and social status by an experimental

approach, using the male domestic fowl (Gallus gallus domesticus) as my study species.

Study species

The domestic fowl (Gallus gallus domesticus) is, like its wild ancestor the red junglefowl

(Gallus gallus; Fumihito et al. 1994), a group living species. Natural groups are typically

constituted by a dominant male, a few subordinate males and several females, and group sizes

ranges from pairs to around 10-15 individuals (McBride et al. 1969, Collias and Collias

1996). The sex ratio varies, but is generally equal or slightly female biased (e.g. 2:3-2:5,

males to females), probably due to higher predation on subordinate males in the periphery of

the group (McBride et al. 1969, Collias and Collias 1996). Both males and females form

(most often linear) social hierarchies defined by threats, attacks and avoidance, and males

always dominate over females (Banks 1956, Collias et al. 1994). The fowl is suitable for

studies of the potential link between behaviour and social status for three main reasons. First,

the status of an individual is rather stable and can persist for several years, but last on average

approximately one breeding season in free-ranging flocks of red junglefowl (Collias and

Collias 1996). This is a considerable part of the lifespan of males, which lives up to 5.5 years

in semi-natural flocks exposed to predation (Collias and Collias 1996). However, changes in

groups over shorter time spans can occur and cause changes in the status of individuals, for

example if the dominant male is predated (McBride et al. 1969). Second, dominant males

have higher reproductive success compared to subordinate males (Pizzari and Birkhead 2000,

Wilson et al. 2008), thus the prerequisite for evolutionary consequences of a relationship

  6  

between social dominance and personality traits. Third, dominant and subordinate male fowl

differ quantitatively in behaviour. Dominant males not only perform more courtship

behaviour (Cheng and Burns 1988), but also crow more (a signal of territoriality and

dominance; Leonard and Horn 1995), and spend more time being vigilant compared to

subordinate males (Cornwallis and Birkhead 2008). However, the relationship between

personality traits and social status is unclear.

METHODS

The study population is kept at Tovetorp research station (Björnlunda, Sweden) in six mixed-

sex (sex ratio ~ 1:1), mixed-age (1-10 yrs) groups (15-20 individuals per group) in outdoor

aviaries (approximately 6x10x2 m) with access to chicken houses. All aviaries are furnished

with perches and dust baths, and the animals have ad libitum access to regular chicken food

and water. The experiments were performed during the breeding season (may-september) in

2007 (n males = 36), 2011 (n = 48, of which 9 were reused from 2007) and 2012 (n = 50).

Personality assays

There were no personality assays specifically developed for chickens when I started the work

with this thesis. Therefore, I developed two novel arena tests to measure activity and

explorative behaviour. The design of these were inspired by the open field test commonly

used in applied ethology to measure variation in fear in domestic fowl (often a small barren

arena, e.g. 1 m. in diameter; Jones et al. 1995) and by the novel arena tests commonly used to

measure variation in exploration propensity in passerine birds (commonly a room furnished

with five artificial trees; Verbeek et al. 1994). The arena used in paper I consisted of an

outdoor roofed arena (3x6 m), with peat floor and five artificial trees (50 cm high). The trees

were added to prevent immediate overview of the arena, encouraging the fowl to explore it

(Fig. 1a). The arena was divided in 8 equal-sized subareas by drawing subtle lines in the

substrate, and the number of subareas visited was used as a measure of exploration

propensity. A personality test should optimally be designed to reflect variation in individual

behaviour within a population (Reale et al. 2007). However, around half of the males retained

the maximum exploration score of visiting 8 subareas in the novel arena. In paper II I

therefore used a larger arena (~ 7x10 m oval, divided into 36 equal-sized subareas; Fig. 1b)

placed in the forest, without a roof, in order to approve of more variation in explorative

behaviour. The forest floor was naturally covered with leafs, herbs and bushes, as in the

 7  

natural habitat of Red junglefowl (Collias et al. 1964). A full description of the behavioural

responses measured in the novel arena tests are given below.

Figure 1. The novel arena-test used as a personality assay in (a) paper I, and (b) paper II.

Startle tests are commonly used to estimate variation in risk-taking behaviour within the

research field of personality (van Oers et al. 2004, Bell 2005, Quinn and Cresswell 2005,

Briffa et al. 2008, Rudin and Briffa 2012). In general a stressor (a sound, a predator model

etc.) is presented, and thereafter the latency until the individual retain regular activities like

feeding, is measured (e.g. van Oers et al. 2004). The fowl utter alarm calls (loud cackling

vocalisations) in response to terrestrial predators, to which flock mates react on by vigilance

(Evans et al. 1993). In paper II I therefore used a recorded male fowl alarm call as a startle.

The latency until the male retained normal activities after the call was played, thus stopped

being vigilant and resumed feeding, was used as a measure of how alert the male was, or in

other words how risky the individual appreciated the environment to be.

Morphological measures

Male body size and comb size (a fleshy red ornament on the head) often correlate positively

with social status in male fowl (Ligon et al. 1990; Zuk and Johnsen 2000; Parker et al. 2002),

and are also shown to interfere with the establishment of social status (Parker et al. 2002).

Males I used, were therefore matched for these morphological features in both studies (to the

nearest 10%). Come size, approximated by comb length and body size, approximated by

tarsus length and body weight, were measured prior to the experiments, at the day of the pair

setup (paper I), or at the day of isolation (paper II).

(a)   (b)  

  8  

Paper I

To study the influence of social status on the expression and consistency of behaviours, I

experimentally changed status of male fowl between repeated personality assays. Pairs of

matched males were set up, and the dominance order of the two males was determined. After

acclimatising to the new social situation, a novel arena test was performed in order to

investigate their boldness (latency to enter the arena), activity (no. of subarea transitions) and

explorative behaviour (no. of subareas visited). The males' vigilance (proportion of time a

male spent being vigilant) was also registered, as was the number of crows (a vocal territorial

display, Collias et al. 1964, Leonard and Horn 1995). Then pair members were

experimentally changed so that the two previously dominant males formed a new pair, and

the two subordinate males another pair, forcing one male in each pair to change social status,

as there can only be one dominant male and one subordinate male in each pair (Fig. 2; see

Cornwallis and Birkhead 2007, 2008 for previous use of this design). After two days of

acclimation to the new social context, the novel arena test was performed once again in order

to estimate the influence of change of social status on behaviour.

Figure 2. Schematic picture of the design used when manipulating social status of male fowl. Males were either

A) dominant across both pair set-ups, B) increased status from subordinate to dominant, C) reduced status from

dominant to subordinate, or D) were subordinate over both pair set-ups.

Setup  1              Setup  2

A

B  

C

D  

B

D  

A

C  

A:  Dominant  -­‐  Dominant  

C:  Dominant  –  Subordinate  

B:  Subordinate  –  Dominant  

D:  Subordinate  -­‐  Subordinate  

 9  

Paper II

To investigate the role for personality on establishment of status, I scored individual

behaviour in a novel arena test and a startle test (play back alarm sound of a conspecific, see

above). In paper II I added the latency to visit at least five subareas as a complementary

measure of exploration propensity (Verbeek et al. 1996). Besides this additional measure, the

behavioural measures were the same as in paper I. All males were isolated from same-sex

competitors for five days prior to the behavioural tests in order to standardise their previous

social experience. After personality was assessed, males were set up in duels resulting in one

male becoming dominant and the other subordinate. The agonistic interaction between males

started spontaneously they were placed in front of each other, and the initial reaction to the

duel situation was used to score the males' aggressiveness from 1-4 (Fig. 3). The males

aggressiveness was scored between 1 (least aggressive) and 4 (most aggressive) as follows:

(1) fleeing away from the other male, (2) straight body posture, no avoidance or attraction to

the other male, (3) crouched body posture and dropped wing or raised hackles (Collias 1943,

Kruijt 1964) or (4) directly – within 2 seconds – approaching the other male (Fig. 3). All

duels ended with one of the opponents retreating and no longer retaliating further attacks

from the opponent. A minimum of five occasions of avoidance within an hour by the same

male was used to define a male as subordinate, and the other male as dominant.

Although I only measured behavioural responses once, and thus did not explicitly evaluate

their repeatability, similar responses have been found to be consistent within the individual in

an earlier study of male fowl (paper I). Moreover, a number of studies in other species have

shown that explorative behaviour and boldness typically show substantial repeatability over

time (e.g. Verbeek et al. 1994, Dingemanse et al. 2002, Quinn and Cresswell 2005). I

therefore consider the single measurement in this study as useful for determination of

personality types.

  10  

Figure 3. Illustration of body postures used for scoring aggressiveness. Picture of a male having a (a) non-

aggressive body posture (upright body posture, score 2) and (b) aggressive body posture (i.e. raised hackles, a

crouched body position and dropped wing, score 3).

SUMMARY OF RESULTS

Paper I

There were several behavioural differences observed between dominant and subordinate

males. Dominant males were more vigilant and active and crowed more compared to

subordinate males, but did not differ significantly in exploration and boldness in the first trial

of the novel arena test (see Fig. 1 in paper I). The main result of this study was however that

some of these responses (vigilance, activity and exploration, Fig. 4 b-d; Table 2 in paper I)

were plastic and changed in frequency when social status was changed, while others were not

(boldness and crowing Fig. 4a, 4e). At the same time, there was a significant relationship

between behaviour in the first and the second trial for all behavioural responses. In other

words, the individual behaviours we recorded were partly stable over time, and change of

status.

Paper II

Among the behaviours observed in the novel arena test in paper II, exploration was the only

response that could forecast social dominance. The quantitative difference in exploration

between future dominant and subordinate males was fairly large; dominant males explored

the novel arena were more than twice as fast as the subordinate males (dominant

243.92±57.16 s., subordinate 500±96 s., Fig. 5). In contrast, there were no significant

(a)   (b)  

 11  

differences in activity, vigilance, alertness after being startled, or crowing between future

dominant and subordinate males (Fig. 5). Aggressiveness in the first seconds of duels could

also predict a dominant position (Fig. 6), and males that showed a higher aggressiveness

more often won the duel. Exploration and aggressiveness were not significantly correlated,

thus not forming a behavioural syndrome along a proactive-reactive axis (Table 1), but

instead independently predicted a dominant social position.

Figure 4. Behavioural response of dominant and subordinate males during the first and second test trial of a

repeated novel arena test. (a) Boldness (whether the males entered the novel arena within 30 s. or not) was stable

within the individual across changes in social status. (b-d) Males that had a stable status across trials showed

more stable behavioural responses of exploration, activity and vigilance compared to males that changed social

status, irrespective of their social status. (e) The number of crows uttered in the second trial was significantly

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affected by previous, but not current, social status, and no clear effects of the change in status were detected.

Values presented are mean ± SE for (b-e), but for (a) the percentages of males that entered the arena within 30

seconds ± 95% CI, are given.

Figure 5. Difference in behavioural response in the novel arena test (a-e) and the startle test (f) between males

that later became dominant (filled dots), or subordinate (empty dots), respectively. Future dominant males were

more explorative compared to subordinate males. All other differences were non-significant. Mean values ± SE

are given.

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Figure 6. Difference in aggressiveness score between males that subsequently became dominant and

subdominant. Males that later won the duel and obtained a dominant social position more often had a higher

aggressiveness score compared to the later subordinate male. However, both males of a pair had equal

aggressiveness score in nearly half of the cases.

To sum up the main results of both papers, dominant and subordinate males differed

quantitatively in several behavioural aspects in non-social contexts. These differences were

partly a result from the current social status (paper I), but also existed prior to the

establishment of social status (paper I and paper II). Together the results reveal a two-way

causality between social position and individual behaviour.

DISCUSSION

In this thesis, I investigated the causality of the relationship between individual behaviour and

social status in male fowl. Dominant and subordinate males differed in several behavioural

responses in a non-social context, and by an experimental approach I showed that the current

social status primarily causes these differences (paper I). However, in paper II I showed that

whether a male end up being dominant or subordinate is not random with respect to

personality types, but influenced by males' personality.

Dominant males were more vigilant, explorative and active, and the occurrence of these

behaviours changed after the experimental change in social status (Fig. 1b-d, Table 2 in

paper I). This meant that individual males adjusted their level of expression of these

behaviours according to their current social status, supporting the first scenario of the

causality of the relationship between social dominance and behaviour. In a study of male

fowl by Cornwallis and Birkhead (2008), vigilance was similarly found to be a plastic

response which frequency changed when social status was changed. It has earlier been

# of

due

ls

0

2

4

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8

10

12

Dom>Sub Sub>Dom Dom=Sub

  14  

demonstrated in male fowl that dominants suppress the behaviour of subordinates (Leonard

and Horn 1995, Johnsen et al. 2001). The quick change in behaviour following a change in

social status (paper I) indicates that subordinate males have an intrinsic capability of

becoming dominant and behaving thereafter, but that such behaviour seem to be suppressed

by the presence of a more dominant male (Wilson et al. 2009). In addition, all males behaved

in a dominant manner already after a very short period of isolation from other males

(personal observation, paper II; see also Pizzari et al 2007 for rapid changes in male

reproductive physiology associated with alteration of status). This indicates that variation in

responses to personality assays do not necessarily reflect fixed behavioural types, but may

reflect the current social position of the individuals. This is in congruence with studies of

male rats (Rattus norvegicus) brought up under various social regimes, showing that social

position affects behaviour also in non-social test situations (Arakawa 2006). The strong effect

of social status indicates that status may act like a ‘state’; a slow changing condition that

infers stability also in behavioural response (Wilson et al. 1994, Dall et al. 2004). Despite the

intuitiveness of the idea of stabilising (external) states causing consistent behaviour, there is a

lack of empirical studies explicitly testing this idea. However, there is one example; a study

investigating Siamese fighting fish (Betta splendens), which demonstrated that holding a

territory stabilise individual behaviour (Dzieweczynski and Forrette 2013), a phenomenon

closely related to social position. Part of the behaviour remained stable across the change in

status in our study, which means that other states and/or heritability also play a role in

shaping individual behaviour. In the study by Cornwallis and Birkhead (2008), no such

behavioural consistency was detected across a change in social status. Behaviour was

monitored in a social context in their study, and it therefore appears that social status has an

even stronger effect in the presence of conspecifics, overriding individual differences. In

another study, male vocalisations (Nelson et al. 2008) were shown to correlate across

functional contexts only when the males were observed in their (stable) social groups, further

strengthening this conclusion.

Dominant and subordinate males differed in crow rate during the first novel arena trial, and

little plasticity was observed in this behaviour when social status was changed. Individual

males seemed to vary in their underlying propensity to crow and this supports the second

scenario outlined previously where social status and behavioural responses share a common

underlying cause. A potential underlying factor for crowing and social dominance could be

testosterone, which regulates development of crowing frequency in male fowl (Davis and

 15  

Domm 1943). Further, males fowl with a high testosterone level have shorter attack latencies

and more often become dominant (Johnsen and Zuk 1995). Indeed, a high crow rate in the

novel arena test was predictive of dominance, although the study in paper I was not

specifically designed to test predictors of status. The latter result was not repeated in paper

II, thus the predictive value of crow rate for social status is questioned. A potential

explanation for this discrepancy could be that the social settings prior to the novel arena test

affects crowing in the arena. In paper I, males were housed in pairs, which forces the

subordinate male to reduce its crowing frequency, since dominant males punish subordinate

males that crow (Leonard and Horn 1995). This might have reinforced the difference in crow

rate between males that were high or intermediate in relative dominance ability (that were

dominant in one or two pair setups) and males that were repeatedly found in subordinate

positions (subordinate in both trials, Fig. 4). In contrast, males were individually caged for

five days prior to the arena test in paper II, thus no males were suppressed in their crowing.

In paper II I performed additional tests to investigate the possibility that behavioural type

could predict future social status, thus testing the third causality scenario; that personality

affects social status. Males that were either more explorative or aggressive had increased

chances of obtaining a dominant position. The results indicate that pre-existing differences in

behavioural type affected the outcome of duels, in other words that not all individuals had

equal chances of obtaining a dominant position. These traits were uncorrelated and equally

strong predictors of social status, suggesting that multiple factors are important for winning a

fight. Scoring high in these traits is considered proactive on the proactive-reactive-continuum

(Koolhaas et al. 1999, Sih et al. 2004b), and the results are therefore in congruence with

studies of other species, which show a general pattern of more proactive individuals having

higher chances of becoming dominant (e.g. Huntingford 1976, Verbeek et al. 1996, Colleter

and Brown 2011, Dahlbom et al. 2011, David et al. 2011). However, there are a couple of

examples of less bold or less explorative individuals having higher chances of obtaining

dominant positions (Gomez-Laplaza 2002, Fox et al. 2009). In a study of great tits, the

success of individuals differing on a proactive-reactive axis differed depending on the

intensity of intraspecific competition over space and food (Dingemanse et al. 2004),

indicating that fitness of different personality types might be context dependent. Fitness of

different personality types under various environmental conditions, as well as the exact

pathway through which these personality traits affect the outcome of duels warrants further

investigations.

  16  

The remaining suggested scenario, that there is no causal relationship between social status

and behavioural response, was observed for only one behavioural response: boldness. There

was no difference in latency to enter the novel arena between males of different social status,

and the change in social status did not alter the latency to enter the arena in the second trial.

However, a recent study of sea anemones (Actinia equine; Rudin and Briffa 2012) showed

that boldness (measured as response to a startle) decreased after the experience of losing a

fight. This indicates that the social environment can affect also boldness in some cases.

The results of this thesis clearly show that social status must be taken into account during

studies of individual behaviour in group-living animals. It is preferable that the social status

of the individual, and the eventual changes of the same, is known during the course of the

study. Other properties of the individual like quality of territory or partner, properties may

potentially affect individual behaviour in a test context in a corresponding way in solitary

species or species with a less clear hierarchical structure of the dominance relationships.

Future prospects

Under natural conditions, several aggressive interactions may follow after one another. In a

socially hierarchical species like the fowl, individuals need to settle the dominance

relationships to all other group members of the same sex, for example when an individual

transfers from one flock to another (Collias and Collias 1996). The ability to recover from a

loss, or the ‘boost’ obtained by a win, have proved to affect the outcome of subsequent duels,

the so-called ‘winner- and loser effects’ (Chase et al. 1994), but it is unknown whether the

magnitude of these effects depend on personality type. In future studies I therefore aim to

investigate how several interactions after each other affect male fowl of different personality

types to improve our understanding of how personality type affect fitness through social

dominance.

 17  

CONCLUSION

In this thesis I aimed to disentangle the commonly observed relationship between variation in

behaviour and social status. I conclude that behavioural differences between dominant and

subordinate male fowl were partly plastic and changed with changes in social status, but also

that the social position of an individual could be a consequence of pre-existing differences in

behavioural style. Plasticity of behavioural responses according to the current social position

have been previously shown in the domestic fowl (Cornwallis and Birkhead 2008), but it is

the first time the effect of personality type on the establishment of social status is shown in

the species. Together, the results of paper I and II reveal a two-way causality between social

position and individual behaviour. This leads to the conclusions that social position should be

taken into account when investigating and interpreting variation in personality, as it could

otherwise act as a confounding factor, and that individual personality type should vice versa

be considered in studies of the underlying reasons of variation in social status.

  18  

ACKNOWLEDGEMENTS

Först och främst vill jag rikta ett stort och varmt TACK till min nuvarande och före detta

handledare Olof Leimar och Tommy Radesäter samt min medförfattare och mentor Hanne

Løvlie, självklart för all hjälp med arbetet med de två studierna i denna avhandling, men

också för att ni uppmuntrar och utmanar mig att utvecklas till en självständig forskare.

Hanne, du ställer alltid upp när jag behöver dryfta stort som smått inom forskningsprojektet,

en riktig klippa, och du har dessutom initierat mig till hönsens fascinerande värld, vilket jag

innerligt glad för. Olle, dig vill jag särskilt tacka för att du generöst delar med dig av

statistisk kunskap och för att du med knivskarp skärpa hjälper mig att förstå de data jag

samlar in.

Jag vill också rikta ett hjärtligt tack till all personal på Tovetorps forskningsstation; Nisse,

Thomas, Sven och "damerna i köket", för att ni alltid är hjälpsamma med allsköns spörsmål,

och för våra glada fikastunder. Utan Minna, Siw, Berit och Anette hade det inte blivit

mycket till ordning på allt administrativt runtomkring, så det vill jag tacka er för. Martin och

Karolina, ni är de bästa rumskompisar man kan önska, i det finaste rummet på hela

institutionen, och jag känner mig verkligen glad när jag varje morgon jäktad ramlar in på

rummet till ert sällskap. Tack också till Sandra, Bea, Kristin, Johanna, Alexandra,

Alexander och alla andra härliga kolleger på Zootis, för alla skratt och alla intressanta

vetenskapliga och ovetenskapliga diskussioner kring lunchbordet (men måste de verkligen

varje gång inkludera någon form av bajsprat? ;).

Tack mamma, för att du alltid stöttar mig och får mig att tro på mig själv. Tack Rikard och

hela tjocka släkten för alla roliga släktträffar som har en omedelbar avslappnande effekt, trots

kakafonin. Tack Magnus för din outsinliga kärlek som bär mig genom tuffa perioder, och för

att du osjälviskt ger mig utrymme att jobbajobbajobba när det behövs. Du är bäst! Och till

sist, tack mina älskade pojkar Vide, Grim och Björn för att ni finns, och gör mitt liv så

mycket bättre!

 19  

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  24  

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 1              

Paper  I    

 

 

   

  1              

Social ‘states’ and personality: Stability in social status and

individual characteristics explain consistency in behavioural

responses

Anna  Favati1,  Olof  Leimar1,  Tommy  Radesäter1  and  Hanne  Løvlie1,2*  

1  Department  of  Zoology,  Stockholm  University,  106  91  Stockholm,  Sweden    

2   Department   of   Physics,   Chemistry   and   Biology,   Linköping   University,   581   83   Linköping,  

Sweden  

*Corresponding  author:  Hanne  Løvlie,  hanne.lovlie@liu.se  

   

   2  

ABSTRACT  

Stability   of   ‘state’   has   been   suggested   as   an   underlying   factor   explaining   behavioural  

stability  and  animal  personality  (i.e.,  variation  among,  and  consistency  within  individuals  in  

behavioural   responses),   but   the   possibility   that   stable   social   relationships   represent   such  

states   remains   unexplored.   Here   we   investigated   the   influence   of   social   status   on   the  

expression  and  consistency  of  behaviours  by  experimentally  changing  social  status  between  

repeated   personality   assays.   We   used   male   domestic   fowl   (Gallus   gallus   domesticus),   a  

social   species   that   forms   relatively   stable   dominance   hierarchies,   and   showed   that  

behavioural   responses   were   strongly   affected   by   social   status,   but   also   by   individual  

characteristics.   The   level   of   vigilance,   activity   and   exploration   changed  with   social   status,  

while   boldness   appeared   as   a   stable   individual   property,   independent   of   status.   Further,  

variation  in  vocalisation  predicted  future  social  status,  indicating  that  individual  behaviours  

can   both   be   a   predictor   and   a   consequence   of   social   status,   depending   on   the   aspect   in  

focus.  Our   results   illustrate   that  social   states  contributed  to  both  variation  and  stability   in  

behavioural  responses,  and  should  therefore  be  taken  into  account  when  investigating  and  

interpreting  variation  in  personality.      

Keywords:   behavioural   syndromes;   intra-­‐sexual   selection;   phenotypic   plasticity;   social  

dominance;  chicken.  

   

   

3  

1.  INTRODUCTION  

Understanding  variation   in  phenotypes   is  a  key   issue   in  evolutionary  biology  [1].  The  topic  

includes  the  study  of  animal  personality,   in  the  form  of  consistent  individual  differences  in  

behaviour,  across  time  and/or  situations  [2],  also  referred  to  as  temperaments  [3]  or  coping  

styles  [4].  The  phenomenon  has  been  described  in  a  large  number  of  species  in  multiple  taxa  

[5],  but  there  are  still  major  gaps  in  our  understanding  of  why  there  is  personality  variation,  

including   unanswered   questions   about   the   mechanisms   behind   stable   behavioural  

responses   and   the   evolution   and   maintenance   of   behavioural   polymorphism   [6,   7].  

Properties   or   circumstances  of  an  individual  that  may  affect  the  costs  and  benefits  of   its  

behaviours,   such   as   size   or   energy   reserves   are   sometimes   referred   to   as   ‘states’   [8].  

Stability   of   such   states   is   theoretically   predicted   to   produce   stability   in   behavioural  

responses   which,   in   combination   with   between-­‐individual   variation   in   state,   gives   rise   to  

variation   in   behavioural   types,   and   thus   personality   [2,   6,   9].   More   broadly,   any   state  

changing  more   slowly   than   behaviour   per   se   is   predicted   to   cause   short-­‐term   stability   in  

state-­‐dependent   behavioural   responses   [2].   Together   with   a   positive   feedback   system,  

stability   in   state   may   also   generate   long-­‐term   stability   of   behavioural   types   [9].   Social  

relationships   such   as   pair   bonds   or   status   hierarchies   could   be   one,   however   not   yet  

investigated,   example   of   such   states.   If   social   positions   or   relationships   constitute   stable  

states,   intra-­‐individual   stability   of   behavioural   responses  would   follow   as   a   consequence,  

whereas  the  behavioural  responses  should  change  when  the  social  state  of  an  individual  is  

changed.  Despite  the  intuitiveness  of  these  predictions,  the  importance  of  social  states  for  

personality  variation  has  not  yet  been  empirically  tested.    

In  social  species,  social  relationships  often  take  the  form  of  dominance  hierarchies,  which  in  

turn   are   based   on   repeated   outcomes   in   favour   of   one   participant   of   dyadic   agonistic  

interactions   [10].   Socially   dominant   individuals   commonly   enjoy   increased   access   to  

resources,  such  as  mating  partners,  which  typically  results  in  a  positive  relationship  between  

social   status   and   reproductive   success   [11].   Aggression   and   the   ability   to   dominate  

conspecifics   can  correlate  positively  with  boldness,  exploration  and  active   stress  handling,  

thereby   defining   a   ‘proactive’   behavioural   style   of   the   reactive-­‐proactive   coping   style  

continuum   [4,   12].   For   example,   explorative   great   tits   (Parus   major)   win   more   fights  

compared   to   less   explorative   ones   [13],   and   bold   three-­‐spined   sticklebacks   (Gasterosteus  

   4  

aculeatus)  are  more  aggressive  than  shyer  individuals  [14].  On  the  other  hand,  boldness  and  

exploration  have  been   found  to  have  a  negative,  or  no  correlation,  with  social  dominance  

[15,  16].   This   indicates   that   the   relationship  between  personality   and   social   status   can  be  

species-­‐specific,   but   also   that   there   are   currently   limitations   to   our   understanding   of   the  

relationship  between  them.    

In   principle,   there   are   three   possible   scenarios   for   observed   correlations   between   social  

dominance   and   personality   traits.   First,   different   social   positions   can   be   associated   with  

different   behavioural   tendencies   [17].   These   differences   can   manifest   themselves   also  

outside   the   social   group,   and   thus   influence   responses   in   personality   assays   [18].   In   this  

scenario,   it   is   expected   that   behavioural   responses   are   flexible,   adjusting   to   the   current  

social   position,   at   least   to   some   extent.   Second,   differences   in   behaviour   can   directly  

influence   the   chance   of   obtaining   a   certain   social   position   (e.g.,   aggression   [19]).   In   this  

scenario,  certain  behavioural   types  are  more   likely   to  be  found   in  specific  social  positions.  

However,  and  crucially,  behavioural  responses  are   independent  of  experimental  change  of  

social   positions.   Third   (and   partially   overlapping  with   the   previous),   behaviour   and   social  

position   can   have   a   common   underlying   cause   [12,   20].   In   such   a   case,   both   personality  

traits  and  the  underlying  cause  (e.g.,  hormonal  state  [20])  might  predict  social  position,  but  

behaviour   is  not  necessarily  altered  when  the  social  position   is  changed.  Although  there   is  

some   support   for   each   of   the   three   scenarios   separately,   they   have   not   previously   been  

tested   simultaneously,   leaving   the   causality   between  behaviour   and   social   status   unclear.  

Our  aim  here   is   therefore   to   investigate   the   issue  by  means  of  an  experimental  approach  

where   social   status   of   individual   male   domesticated   fowl   (Gallus   gallus   domesticus)   is  

changed  and  behaviour  scored  in  personality  assays.  If  a  change  in  dominance  status  leads  

to   a   change   in  behavioural   response,  we   can   conclude   that   social   status  may   represent   a  

state  that  gives  rise  to  consistent  differences  in  behaviour.  

Male   fowl  are  suitable   for   investigating  the  potential   link  between  variation   in  personality  

and  social  status  for  two  main  reasons.  First,  dominance  hierarchies  are  relatively  stable;  the  

status  of  an  individual  persists  for  approximately  one  breeding  season  in  free-­‐ranging  flocks  

of  fowl  [21],  but  changes  in  groups  over  shorter  time  spans  can  occur  and  cause  changes  in  

the  status  of  individuals  (e.g.,  if  the  dominant  male  is  predated  [22]).  Therefore,  status  can  

be   considered   as   a   slowly   changing   yet   not   permanent   state.   Second,   dominant   and  

   

5  

subordinate  male  fowl  differ  quantitatively  in  behaviour.  For  example,  dominant  males  crow  

more,   as   a   signal   of   territoriality,   and   spend   more   time   being   vigilant   compared   to  

subordinate   males   [17,   23].   Nevertheless,   the   causal   relationship   between   these  

behavioural  differences  and  status  is  untested.    

2.  METHODS  

Animals and housing

The  study  took  place  during  the  breeding  seasons  (May  -­‐  September)  of  2007  and  2011  at  

Tovetorp  Research  station,  Stockholm  University,  Sweden.  We  used  84  males  (2007:  n  =  36;  

2011:   n   =   48)   of   an   old   Swedish   game   breed   of   fowl   (Gallus   gallus   domesticus,   ‘Gammal  

svensk   dvärghöna’)   used   to   human   handling   and   kept   under   semi-­‐natural   conditions   in  

mixed-­‐sex,  mixed-­‐age  (1-­‐9  years)  groups.  Data  were  collected  during  the  hours  of  day  when  

the  birds  are  most  active  (0530-­‐1100  and  1500-­‐1900  hours   local   time,  see  [24]   for   further  

information  on  variation   in  daily  behavioural  patterns).  Groups  of   four  males   (ngroups  =  21)  

were  matched   for  morphological   measures   (<   10%   difference   in   comb   and   body   size)   to  

reduce  the  effect  these  variables  can  have  on  the  establishment  of  status  [19,  25,  26].  Comb  

size  and  body  size  were  estimated  as  comb  length  and  tarsus  length  respectively,  measured  

with  a  digital  calipeter  to  the  nearest  tenth  of  a  millimetre.  Body  size  was  also  estimated  as  

body   weight   measured   with   a   digital   scale   to   the   nearest   gram.   To   generate   males   of  

different   social   positions,   two   pairs   of   males   were   randomly   chosen   from   each   of   the  

matched  groups  of   four  males   (npairs  =  42).  Pairs  of  males  were  housed   in  outdoor  aviaries  

(approximately  3  x  3  meters)  that  were  visually,  but  not  vocally,   isolated  from  other  birds.  

This   set   up   resulted   in   one   of   the  males   in   each   pair   becoming   dominant,   and   the   other  

subordinate.  A  minimum  of  five  observed  successive  submissive  behaviours  within  2  hours  

(avoiding  the  other  male  when  he  approached)  by  a  male  defined  that  male  as  subordinate  

[27].  Males  within   a  pair   had  not  been  housed   together   for   at   least   2  weeks  prior   to   the  

trials,  reducing  any  effects  earlier  encounters  may  have  had  on  the  establishment  of  social  

status  [28,  29].  All  birds  had  ad  libitum  access  to  food  and  water,  and  all  aviaries  had  dust  

baths   and   perches.   Experiments   were   conducted   according   to   ethical   requirements   in  

Sweden  (Linköping  Ethical  committee,  ethical  permission  number  60-­‐10).  

Behavioural assays and manipulations of social status

   6  

Two   days   after   the   pair   was   formed,   which   was   enough   time   for   males   to   establish   a  

dominance   relationship  without   reversals,  each  bird  was  exposed   to   its   first   ‘Novel  arena’  

test  (referred  to  as  trial  1)  in  a  3  x  6  meter  large  outdoor  area  connected  to  the  aviary  by  a  

door.   The   order   of   testing   of   the   males   in   a   pair   was   random   with   respect   to   social  

dominance.  The  floor  in  the  arena  was  covered  with  dark  brown  peat  to  create  novelty  (in  

comparison   to   the   sandy   floor   of   the   birds’   home   pens)   and   divided   into   8   subareas   by  

drawing  subtle  lines  in  the  floor  substrate  to  facilitate  estimates  of  exploration  (see  below).  

The  arena  had  five  artificial  bushes  (green  plastic  spruce  trees,  approx.  70  x  50  cm)  in  order  

to  obstruct  direct  view  of  the  arena  and  thus  encourage  exploration  (see  S.I.,  figure  S1).  The  

cage  mate  of   the   focal  male  was   removed   from   the  aviary  by  herding  him   into  an  empty  

adjacent  pen  two  minutes  before  the  test  started.  The  door  between  the  aviary  and  the  test  

arena   was   opened,   and   focal   males   that   entered   the   arena   within   30   seconds   were  

considered  bold,  while  those  who  did  not  were  considered  shy  (i.e.,  a   ‘boldness’  spectrum  

split  into  two  categories,  becasue  of  a  bimodal  distribution  of  the  latencies).  In  cases  when  a  

male  did  not  voluntarily  enter  the  arena  within  2  min,  he  was  gently  herded  into  it  by  the  

observer.  The  observer  sat  outside  the  arena,  visible  to  the  male  during  the  test.  Behaviours  

and   vocalisations   were   recorded   for   15   min,   starting   when   the   male   entered   the   arena.  

Vigilance   (head   above   shoulder   height,   eyes   open)   and   behaviours   categorised   as   non-­‐

vigilance  (eating,  preening,   resting  and  dust  bathing,  behaviours  that  all  occurred   in   lower  

frequencies)  were  recorded  every  30s,  and  the  percentage  of  recordings  a  male  was  vigilant  

during  the  test  was  calculated  (hereafter  named  ‘vigilance’).  The  number  of  unique  subareas  

a   male   visited   (1-­‐8)   divided   by   the   total   number   of   possible   subareas   (8)   was   used   as   a  

measure  of  ‘exploration’  propensity.  The  number  of  times  a  male  entered  a  subarea  he  had  

previously  visited,  was  noted  as  a  measure  of  ‘activity’.  Number  of  crows  were  recorded  ad  

libitum  (‘crowing’).  Crowing  is  a  species-­‐specific  vocalisation  related  to  territoriality  in  male  

fowl   [30].   In   addition   to   crowing,   some   males   uttered   alarm   calls,   which   are   loud   and  

distinct  warning   vocalisations   typically  uttered  when  an   individual   is   startled,   for   example  

when  a  predator  appears  [31],  but  these  few  vocalisations  were  not  analysed  further.    

When  the  behaviour  of  all  four  males  of  a  matched  group  had  been  scored  in  the  first  novel  

arena  test,  pair  members  were  experimentally  changed  so  that  the  two  previously  dominant  

males  formed  a  new  pair,  and  the  two  subordinate  males  another  pair.  The  new  pair  setup  

   

7  

forced  one  male   in   each  pair   to   change   social   status,   as   there   can  only   be  one  dominant  

male  and  one  subordinate  male   in  each  pair  [see  18  for  previous  use  of  this  design].  After  

two  days  of   acclimation   to   the  new   social   context,   the  novel   arena   test  was  performed  a  

second  time  in  order  to  estimate  the  influence  of  change  of  social  status  on  behaviour  [26].  

We  refer  to  this  test  as  trial  2.  For  the  second  pair  setup,  the  number  of  males  was  reduced  

to  82  due  to  the  death  of  one  male  in  2007  and  injury  of  one  male  in  2011.  A.  F.  conducted  

all  observations.    

Statistical analyses

Our   general   approach   to   the   statistical  modeling   of   the   behavioral   responses  was   to   first  

determine   suitable   Box-­‐Cox   transformations   of   the   continuously   distributed   responses,   in  

order   to   achieve   homogeneous   variances.   The   outcome   of   this   procedure   was   that   the  

measure  vigilance  did  not  need  transformation,  the  transformation  (𝑥 + 1)!.!"  was  used  for  

activity   and   crowing,   and   the   transformation   𝑥!  for   exploration.   We   applied   these  

transformations   in   all   analyses,   including  model   selection   and   Bayesian  MCMC  modeling,  

but  we   show   the  untransformed  variables   in   the   figures.   The  binary  measure  of  boldness  

was   treated   as   a   discrete   variable.   Based   on   our   experimental   design,   with   males   being  

divided  into  matched  groups,  we  used  the  group  as  a  random  effect  in  mixed  models  of  the  

behavioral  responses.  

Difference in behavioural responses of dominant and subordinate males in trial 1

To   investigate   differences   in   behavioural   response   between   dominant   and   subordinate  

males  (n  =  84),  we  analysed  the  effect  of  social  status  on  each  response  (boldness,  vigilance,  

activity,   exploration  and  crowing)   in   trial   1,  by   fitting  mixed  models  with   the   trial  1   social  

status   as   a   fixed  effect   and   the  group  as   a   random  effect   (Bayesian  Markov  Chain  Monte  

Carlo  generalized  linear  mixed  models,  MCMCglmm,  [32]).    

Individual characteristics versus the effect of social status on behavioural responses

Behavioural  response  in  the  second  trial  can  be  dependent  on  behavioural  response  in  the  

first  trial  (i.e.,  personality),  current  social  status  (thus  behaviour  is  a  plastic  response)  or  the  

previous   social   status   (suggesting   a   common  underlying   variable).   In   order   to   disentangle  

the  effect  of  social  status  and  personality  on  a  behavioural  response,  we  analysed  the  effect  

   8  

of  both  ‘current  status’  (obtained  in  the  second  pair  setup,  ‘dominant’  vs.  ‘subordinate’)  and  

‘previous   status’   (obtained   in   the   first   pair   setup,   ‘dominant’   vs.   ‘subordinate’),   and  

behavioural   response   in   the   first   trial   on   each   of   the   responses   in   the   second   trial   by  

Bayesian  MCMCglmm  (n  =  82).  Random  effect  and  error  distributions  were  the  same  as   in  

the  previous   analyses   (above).   To  determine   final  models,  we  used  bidirectional   stepwise  

selection   choosing   the   model   with   the   lowest   AIC   value   using   Generalized   linear   mixed  

model  [33].  The  minimal  model  for  each  response  in  the  second  trial  was  set  to  include  the  

corresponding  response  from  the  first  trial,  current  status  and  previous  status.  The  range  of  

models  used   in  stepwise  search  of  the  best  fitted  model   included  all   response  variables   in  

the  first  trial,  current  status  and  previous  status.  We  also  estimated  repeatability  with  and  

without  taking  social  status  into  account  (see  S.I.).  

Factors predicting social status

Comb  size,  body  size  (tarsus  length,  and  body  weight)  and  age  are  traits  that  may  affect  the  

establishment  of  status   in  male  fowl  [19].  We  investigated  whether  the   initial  matching  of  

males  for  these  properties  was  successful  in  both  pair  setups  by  testing  for  the  difference  in  

comb   size,   body   size,   body  weight   and   age   between   dominant   and   subordinate  males   in  

each  pair   by  means  of   a   two-­‐sided,   one-­‐sample   student’s   t-­‐test.   The   level   of   this   analysis  

was   thus   the   pair   (ntrial1   =   42,  ntrial2   =   40).   To   investigate  whether   behaviour  may   predict  

social  status,  we  tested  if  behavioural  response  in  the  first  novel  arena  test  could  predict  the  

outcome   of   the   duel   in   the   second   pair   setup.   Difference   between   dominant   and  

subordinate  males  in  the  binary  response  boldness  was  tested  with  Fisher’s  exact  test,  while  

difference  in  vigilance,  activity,  exploration  and  crowing  between  dominant  and  subordinate  

male  of  each  pair,  were  tested  with  a  two-­‐sided  one-­‐sample  student’s  t-­‐test  (npairs  =  41).  

All  statistics  analyses  were  conducted  using  R  version  2.15.1  [34].    

3.  RESULTS    

Differences in behavioural responses of dominant and subordinate males

Dominant  males  were  more  vigilant  and  active,  and  crowed  more  compared  to  subordinate  

males,  but  did  not  differ  significantly  in  boldness  and  exploration  (table  1,  figure  1).  

Individual characteristics versus the effect of social status on behavioural responses

   

9  

Analyses  of  factors  affecting  the  observed  behavioural  responses  of  males  in  the  second  trial  

showed   that   all   response   variables   investigated   had   a   statistically   significant   positive  

relationship  with  the  corresponding  response  in  the  first  trial  (table  2).  At  the  same  time,  all  

responses  but  boldness  and  crowing,  were  affected  by  the  current  social  position  (table  2,  

illustrated  by   figure  2  showing  variation   in  vigilance,   for  other  variables  see  S.I.   figure  S2).  

Vigilance,   activity  and  exploration  were   flexible  behaviours  and  changed   to  a   large  extent  

with   changed   social   status   (table   2,   figure   3b-­‐d).   This   was   especially   pronounced   for  

vigilance  (figure  3b),  while  for  example  boldness  did  not  follow  changes  in  status  (figure  3a).  

Males  that  had  changed  status  clearly  altered  the  time  they  spent  being  vigilant:  males  with  

reduced   status   from   dominant   to   subordinate   showed   a   decrease   in   vigilance,   while   an  

increase   in   vigilance   was   seen   in   males   that   improved   their   status   from   subordinate   to  

dominant   (figure   3a).   Males   with   stable   status   across   the   two   experimental   pair   setups  

(males   that   remained   either   dominant,   or   subordinate)   showed   a   stable   between-­‐test  

response  (figure  3a).  The  number  of  crows  uttered  by  males  was  dependent  on  the  previous  

social   status:  males   that   previously   had   been   dominant   crowed  more   in   the   second   trial  

compared  to  other  males,  irrespective  of  their  current  social  status  (table  2,  figure  3e).    

There  were  additional  statistically  significant  factors   influencing  the  behavioural  responses  

of   males   in   the   novel   arena   test   of   trial   2   (table   2).   Part   of   variation   in   vigilance   was  

explained  by  the  number  of  crows  a  male  uttered  in  the  first  trial,  thus  males  that  crowed  

more   in   the   first   trial   were   more   vigilant   in   the   second   trial   (table   2).   In   a   similar   way,  

activity  was  partly  explained  by  vigilance   in  trial  1,  and  crowing  was  affected  by  activity   in  

trial  1  (table  2).    

Factors predicting social status

None   of   the   measured   morphological   traits,   or   age,   had   a   detectable   effect   on   the  

establishment  of  social  status  in  this  experiment,  indicating  that  the  experimental  matching  

for  these  features  was  successful  (first  pair  setup:  tarsus  length,  t41  =  -­‐0.080,  p  =  0.94;  body  

weight,   t41   =   0.36,   p   =   0.72;   comb   length,   t41   =   -­‐1.03,   p   =   0.31;   age,   t41   =   0.49,   p   =   0.63,  

second  pair   setup:   tarsus   length,   t40  =  0.76,  p  =  0.45;  body  weight,   t40  =  0.0072,  p  =  0.99;  

comb  length,  t40  =  1.71,  p  =  0.09;  age,  t40  =  -­‐0.14,  p  =  0.89).  On  the  other  hand,  the  number  

of   crows   a  male   uttered   in   the   first   trial   predicted   future   social   status   in   the   second  pair  

   10  

setup;  males  that  crowed  more  had  a  higher  probability  of  becoming  dominant  compared  to  

males   that   crowed   less   (t40   =   2.59,   p   =   0.01).   No   other   behavioural   responses   predicted  

future  status  (boldness,  p  =  0.58;  vigilance,  t40  =  0.41,  p  =  0.68;  activity,  t40  =  -­‐0.73,  p  =  0.47;  

exploration,  t40  =  0.78,  p  =  0.44).  

4.  DISCUSSION  

Our  experiment   showed   that  behavioural   responses  of  male  domestic   fowl   in  behavioural  

assays   are   affected   both   by   the   social   status   of   an   individual   and   by   its   individual  

characteristics.   Our   results   support   the   general   interpretation   of   behaviours   being   plastic  

but  also  showing  constraints  in  flexibility,  in  line  with  the  few  empirical  studies  where  both  

possibilities   have   been   investigated   [35,   36].   How   the   two   factors   social   position   and  

individual  characteristics  explain  variation  and  stability   in  a  behavioural   response  depends  

on  the  behavioural  response  in  focus,  and  will  be  discussed  below.  

We   introduced   three   scenarios   for   how   a   relationship   between   social   position   and  

behavioural  responses  can  come  about.  By  exploring  different  aspects  of  behaviour  of  male  

fowl  across  changes  in  social  position,  we  found  experimental  support  for  two  of  the  three  

scenarios,   namely   that   the   social   position   in   itself   influences   behaviour,   and   that   social  

position   and   behaviour  may   share   a   common,   underlying   cause.   According   to   the   first   of  

these,   frequencies   of   behaviours   are   expected   to   change   when   social   status   changes,  

thereby  putting  a  limit  to  the  consistency  of  the  individual  responses.  We  found  this  to  be  

the  case  for  three  of  the  recorded  responses:  activity,  exploration  and  vigilance.  Activity  and  

exploration  are  commonly  used  behavioural  dimensions   in  personality   studies   [3],  but   the  

effect  of  social  status  on  their  expression  has  previously  not  been  investigated.  In  the  fowl,  

dominant   males   guard   territories   [30].   The   increased   activity   and   exploration   observed  

when  a  male  becomes  dominant  may  thus  be  explained  by  an  increased  propensity  to  patrol  

a   territory   and   its   surroundings.   Our   results   support   the   general   idea   that   individuals  

obtaining  dominant  social  positions  are  more  often  observed  to  behave  in  a  proactive  way,  

rather  than  in  a  reactive  manner  [4,  13,  20].  They  further  suggest  that  an  individual’s  degree  

of  activity  and  exploration  is  partly  a  consequence  of  the  current  social  situation,  and  stays  

constant  if  social  status  is  unchanged,  but  changes  when  social  status  changes.  This  is  in  line  

   

11  

with   the   reasoning   of   Dall   et   al.   [2],   who   suggested   that   stability   in   various   states   can  

underlie  consistency  in  behavioural  responses.    

Vigilance   decreases   predation   risk   by   facilitating   early   detection   of   predators   and   can   be  

considered  a  response  to  an  individual’s  assessment  of  risks  in  its  environment  [37].  Both  in  

our  study  and  as  previously  shown  [17],  dominant  males  were  more  vigilant,  and  the  degree  

of  vigilance  changed  dramatically  when  status  changed,  which  can  be  interpreted  as  a  risk-­‐

averse  response  to  protect  increased  assets  (e.g.,  access  to  females  as  sexual  partners)  [6].  

Such  a  response  follows  the  principle  of  asset  protection,  in  that  individuals  should  increase  

their   cautiousness   when   assets   increase   [38,   39].   However,   it   has   been   argued   that  

differences   in   state   should   converge   over   time,   as   cautiousness   is   assumed   to   lead   to   a  

decrease   of   assets   [9].   We   do,   however,   not   expect   increased   access   to   females   -­‐   as   a  

consequence  of  high  social  status  -­‐  to  be  negatively  affected  by  an  increased  vigilance,  thus  

the  relationship  between  asset  and  behaviour   in  this  case  need  not  function  as  a  negative  

feedback  mechanism   that   causes   a   convergence   of   individual   states.   Our   results   indicate  

that   social   status   could   act   as   a   stabilising   condition,   or   ‘state’,   generating   at   least   short-­‐

term  stability  in  behavioural  responses  [39,  40].  Whether  long-­‐term  stability  is  achievable  in  

a  similar  way  remains  to  be  studied.  This  could  happen  if,  for  example,  early  experiences  of  

dominance  positions   lead   to   long-­‐term   individual  differences   in  physiology  or  morphology  

that  later  in  life  affect  the  chances  of  obtaining  a  certain  social  position.    

We  also  found  support  for  the  scenario  that  behaviour  and  social  dominance  share  common  

underlying   causes.   The  number  of   crows  uttered  by   a  male  was   correlated  with  both   the  

previous   social   status   and   the  behavioural   type  of   an   individual,   indicating   that   individual  

males  vary  in  their  underlying  propensity  to  crow  and  that  this  propensity  can  influence  the  

chances   of   becoming   dominant.   The   observation   that   dominant   males   crow   more   than  

subordinates  has  been  reported  previously  in  the  species  [17,  23],  but  to  our  knowledge  our  

study   is   the   first   observation   of   an   effect   of   social   position   on   number   of   crows   uttered  

outside  of   a   social   context.   Also,  we   found   that  when   two  dominant,   or   two   subordinate  

males,  were  paired  up  in  preparation  for  the  second  trial,  the  male  that  had  crowed  more  in  

the   preceding   novel   arena   test   more   often   became   dominant.   Our   observations   thus  

suggest   that   crowing   frequency  partly   reflects   an  underlying   characteristic   that   influences  

the   establishment   of   social   status   [20,   41,   42].   Note,   however,   that   crowing   is   not   a  

   12  

commonly  observed  behaviour  during  the  interactions  that  determine  social  status;  it  rather  

appears  as  a  signal  of  the  outcome  [23,  43].  A  potential  underlying  factor  for  crowing  and  

social  dominance  could  be  testosterone,  which  regulates  development  of  crowing  frequency  

in  male  fowl  [44].  A  higher  testosterone  level  during  male-­‐male  interaction  has  been  found  

to  be  associated  to  shorter  attack   latencies  and  an  increase   in  the  probability  of  obtaining  

high   social   status   in  male  domestic   fowl   [45].   Further   studies  of   the   relationship  between  

crowing,  behaviour  during  duels  and  hormonal  status  could  help  elucidate  why  crowing  in  a  

non-­‐social  situation  not  only  signals  high  social  status,  but  also  predicts  it.  

Our   experimental   design   did   not   allow   an   explicit   and   thorough   test   of   the   remaining  

scenario;  that  behaviour  per  se  leads  to  a  certain  social  position,  because  males  in  our  study  

had   already   obtained   a   social   position   prior   to   the   first   personality   test.   Behavioural  

responses  from  personality  assays  have  sometimes  proved  to  be  predictive  of  future  social  

status   [4,   13],   but   that   possibility   is   not  mutually   exclusive  with   the   two   other   scenarios  

presented  here,  and  thus  remains  to  be  investigated  further.    

Of   the   responses   studied   here,   only   the   level   of   boldness   was   unaffected   by   changes   in  

social  status.  Dominant  males  tended  to  be  bolder  than  subordinate  males  in  the  first  trial,  

but   there   was   no   change   in   boldness   when   status   was   changed.   Compared   to   the   other  

behaviours   we   investigated,   boldness   therefore   appears   to   be   less   flexible,   in   being  

independent  of  changes  in  social  status.  However,  a  recent  study  of  sea  anemones  (Actinia  

equina   [46])   showed   that   the   experience   of   a   fight,   and   in   particular   for   the   losing   part,  

decrease  boldness  (latency  to  retain  regular  activity  after  being  startled).  This  indicates  that  

the  social  environment  can  affect  also  boldness.    

In  addition  to  the  sometimes  striking  effect  of  social  status  on  behavioural  responses  in  our  

study,  there  was  always  a  remaining  correlation  between  the  responses  of  individuals  across  

the   two   test   occasions.   This   consistency   in   behaviour   across   social   situations   is   an  

expression   of   individual   characteristics   that   fall   under   the   general   heading   of   animal  

personality,   but   the   precise   nature   and   general   significance   of   these   characteristics   is   an  

open  question.  Studies  on  other   species  have  shown  that  heritable  components,   together  

with  early  life  experiences  (e.g.,  maternal  effects),  can  partly  explain  variation  and  stability  

of   individual   behaviour   [47,   48].   Less   attention   has   been   directed   to   how   intrinsic   or  

   

13  

environmental  factors  later  in  life  may  shape  personality.  An  recent  experimental  study  on  

great  tits  (Parus  major)  showed  that  breeding  effort  is  a  potential  example  of  a  non-­‐genetic  

cause   of   personality   variation   [49],   in   a   broadly   similar   way   as   we   found   here   for   social  

positions.  Our  results  emphasises  the  need  for  controlling  for  stability  in  the  social  context  

that  is  of  importance  for  the  species  in  question  (e.g.,  social  status  and  group  composition),  

and   possibly   stability   also   in   other   contexts   or   dynamic   states,   to   further   improve   our  

understanding  of  causes  and  consequences  of  variation  in  personality.  

ACKNOWLEDGEMENTS  

We  are  grateful  to  N.  Andbjer  for  game  keeping  and  L.  Nauman  for  field  assistance.  OL  was  

supported   by   a   grant   (621-­‐2010-­‐5437)   from   the   Swedish   Research   Council   and   by   the  

Strategic   Research   Program   Ekoklim   at   Stockholm   University.   HL   was   supported   by   a  

fellowship   from   the   Swedish   Research   Council   and   by   a   grant   from   the   Längmanska  

Foundation.    

   14  

Tables

Table  1.  Behavioural  responses  of  dominant  and  subordinate  male  fowl  in  the  first  trial  of  a  

novel  arena  test  (see  main  text  for  further  details).    

response   dominant   subordinate   PMCMC  

boldness   64%   45%   0.060  vigilance   0.79  ±  0.02   0.55  ±  0.03   <0.001  activity     23.00  ±  2.36   12.81  ±  1.97   <0.001  exploration   7.26  ±  0.17   6.69  ±  0.24   0.066  crowing   14.79  ±  1.56   8.55  ±  1.52   <0.001  Values  presented  are  mean  ±  SE  for  all  responses  except  boldness,  where  the  percentages  of  bold  males  are  

shown.  PMCMC-­‐values  <  0.05  are  highlighted  in  bold.  

 

Table   2.   Factors   explaining   variation   in   behavioural   responses  of  male   fowl   in   the   second  

trial  of  a  novel  arena  test  (see  main  text  for  further  details).  

response  trial  2   response  trial  1   status  trial  1   status  trial  2   additional  variables  included    in  model  (from  trial  1)#    

boldness   2.11***   -­‐0.45   -­‐0.37    vigilance   0.27**   -­‐0.05   0.18***   crowing,  0.08*  

activity     0.42***   -­‐0.06   0.23**   vigilance,  -­‐0.84**;  boldness,  -­‐0.14  exploration     0.37**   -­‐11.77   85.38*   boldness,  70.46  crowing   0.37***   0.33***   0.09   activity,  0.22*;  boldness,  -­‐0.15  Values  presented  are  posterior  means  of  model  parameters  in  the  final  MCMCglmm  analyses,  with  effects  of  

status   given   as   dominant-­‐subordinate  differences.   See  main   text   for   the   variable   transformations   that  were  

used   in   the  model   fitting.  The  star  symbols   indicate  statistical   significance:   ‘*’  PMCMC  <  0.05,   ‘**’  PMCMC<0.01,  

‘***’  PMCMC<0.001.  #Inclusion  of  certain  behavioural  responses  from  trial  1  contributed  to  a  better  model  fit.    

   

15  

Figures

Figure   1.   Behavioural   response   of   dominant   and   subordinate   males   in   the   first   trial   of   a   novel   arena   test.  

Dominant  males   (‘dom’,   filled   dots)   (a)   tended   to   be   bolder   (i.e.,   more   often   entered   the   arena   within   30  

seconds),  (b)  were  more  vigilant  (i.e.,  had  higher  frequency  of  time  spent  being  vigilant),  (c)  were  more  active  

(i.e.,   conducted  more   sub-­‐area   transitions),   (d)   tended   to  be  more  explorative   (i.e.,   visited  more   sub-­‐areas),  

and  (e)  crowed  more  often  (i.e.,  number  of  crows)  compared  to  subordinate  males  (‘sub’,  open  dots)  (table  1).  

Values  are  given  as  mean  ±  SE,  except  for  (a),  where  percentages  of  males  that  entered  the  arena  within  30  

seconds  ±  95%  CI,  are  given.  

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Figure   2.   The   effect   of   current   social   status,   and  previous   behavioural   response   (in   trial   1)   on   vigilance   in   a  

second   novel   arena   test   (trial   2).  Males   that   were   dominant   (filled   dots,   solid   line)   spent  more   time   being  

vigilant  compared  to  males  that  were  subdominant  (open  dots,  dashed  line).  At  the  same  time,  vigilance  was  

repeatable  within   individuals  (demonstrated  by  a  positive  slope,  table  2).  Social  status  of  males  presented  in  

the  figure  was  based  on  social  status  obtained  in  trial  2  (see  main  text  for  further  details).  See  S.I.  for  similar  

figures  for  other  behaviours  (figure  S2).    

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Figure  3.  Behavioural  response  of  male  fowl  of  different  social  status  during  the  first  (trial  1)  and  second  test  

trial  (trial  2)  in  a  repeated  novel  arena  test.  (a)  Males  of  different  status  did  not  differ  in  boldness  (i.e.,  equal  

percentage  of  dominant,  filled  dots,  and  subordinate,  open  dots,  males  entered  the  arena  within  30  seconds),  

and   stable   (solid   lines)   vs.   changed   (dashed   lines)   social   status   had   no   significant   effect   on   variation   in  

boldness.   Dominant   males   were   more   (b)   vigilant   (frequency   of   time   spent   being   vigilant),   (c)   active   (i.e.,  

conducted   more   sub-­‐area   transitions)   and   (d)   exploratory   (i.e.,   visited   more   sub-­‐areas),   compared   to  

subordinate  males.  Males   that   had   a   stable   status   across   trials   showed  more   stable   behavioural   responses  

compared   to  males   that   changed   social   status,   irrespective   of   their   social   status.   (e)   The   number   of   crows  

uttered   in   the   second   trial   was   significantly   affected   by   previous,   but   not   current,   social   status.   Values  

presented  are  mean  ±  SE,  except  for  (a),  where  percentages  of  males  that  entered  the  arena  within  30  seconds  

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   18  

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(doi:10.1098/rspb.2012.1936).

 

   

  23              

Paper  II    

 

 

   

 24              

Aggressiveness and exploration predicts social dominance in male

domestic fowl (Gallus gallus domesticus).

Anna  Favati1*,  Olof  Leimar1  and  Hanne  Løvlie1,2  

1  Department  of  Zoology,  Stockholm  University,  10691  Stockholm,  Sweden    

2  Department  of  Physics,  Chemistry  and  Biology,  Linköping  University,  581  83  Linköping,  Sweden  

*Corresponding  author,  anna.favati@zoologi.su.se  

  25  

ABSTRACT

Individuals   in   social   species   commonly   form   dominance   relationships,   where   dominant  

individuals  enjoy  greater  access   to   important   resources  compared   to  subordinates.  Recent  

work   on   animal   personality   (i.e.   consistent   variation   in   individual   behavioural   responses)  

show  that  personality  can  covary  with  social  status,  thus  suggest  that  besides  morphological  

traits,  also  behavioural  variation  can  play  an   important  role   in  establishment  of  status.  We  

investigated   whether   behavioural   responses   in   non-­‐social   contexts   could   predict   the  

outcome   of   duels   of   pairs   of   morphologically   matched   pairs   of   male   fowl   (Gallus   gallus  

domesticus).   Male   fowl   form   social   hierarchies   only   partly   explained   by   variation   in  

morphological   traits,   and   with   unknown   influences   of   variation   in   behaviours.   Several  

behaviours   covary   with   social   status   in   male   fowl,   however   it   is   unclear   whether   such   a  

relationship  is  a  consequence  of  the  dominance  position,  or  a  cause  of  it.  We  show  that  male  

fowl   that   more   quickly   explored   a   novel   arena   were   more   likely   to   obtain   a   dominant  

position.   In   addition,   and   independent   of   exploration   propensity,   males   that   were   more  

aggressive  at  the  start  of  a  duel  also  had  greater  chances  of  becoming  dominant.  Our  results  

therefore  show  that  multiple,  uncorrelated  behavioural  traits,  can  predict  social  status.    

Keywords:   behavioural   syndromes;   intra-­‐sexual   selection;   social   status;   social   hierarchy;  

chicken.  

 26  

INTRODUCTION

In   social   species,   relationships   often   take   form   of   dominance   hierarchies,   commonly  

described  as  the  repeated  win  of  one  individual  over  another  (Chase  1980).  Ornaments  and  

other  morphological   features,   like   body   size,   typically   contribute   to   the   assessment   of   an  

antagonist,  but  do  not  fully  predict  social  rank  (Andersson  1994).  Behavioural  predictors  of  

dominance   have   received   much   less   attention,   even   though   dominant   and   subordinate  

individuals  commonly  differ  quantitatively  in  behaviour.  For  example,  aggression  often  (but  

not  always)  shows  a  positive  correlation  with  social  status  (Verbeek  et  al.  1996,  Kim  and  Zuk  

2000,  McGhee  and  Travis  2010).  Aggression  often  includes  a  heritable  component,  can  have  

a   positive   effect   on   reproductive   success   and   shows   intra-­‐individual   stability   (Smith   and  

Blumstein   2008).   Behaviours   that   are   repeatable   within   the   individual,   but   varies   among  

individuals,   are   also   known  as  personality   traits   describing   an   individual's   personality   type  

(Sih   et   al.   2004b).   Dominance   and   aggression   are   sometimes   included   in   the   concept   of  

coping  styles,  a  composite  personality  classification  typically  describing   individuals  by   their  

speed   of   exploration,   boldness,   and   stress   hormone   profiles   (Koolhaas   et   al.   1999).  

Individuals  scoring  high  on  these  behaviours  are  said  to  have  a  'proactive'  coping  style,  while  

those  scoring  low  are  defined  as  having  a  'reactive'  coping  style  (Benus  et  al.  1987,  Koolhaas  

et  al.  1999,  Schjolden  and  Winberg  2007).  These  traits  are  sometimes  positively  correlated  

within   individuals   (Verbeek  et  al.  1996,  Øverli  et  al.  2004),  but  not  always   (Gomez-­‐Laplaza  

2002,  Weiss  et  al.  2007,  Fox  et  al.  2009,  Weiss  et  al.  2009).  Individual  differences  in  coping  

with  challenges  experienced  during  behavioural  assays  may  reflect  variation   in  coping  also  

with  the  challenge  of  meeting  a  same-­‐sexed  conspecific  in  a  duel  over  social  dominance.  To  

date,  there  are  only  a  few  studies  exploring  the  predictive  power  of  variation  in  personality  

types   for   social   status.   Some   of   these   studies   have   used   lines   selected   for   variation   in  

proactivity   or   aggressiveness,   and   indicate   that   proactive   and   aggressive   individuals   have  

higher   chances   of   obtaining   a   high   social   status   (Benus   et   al.   1990,   Pottinger   and   Carrick  

2001).   However,   studies   of   the   relationship   between   natural   variation   in   personality   and  

social  status  are  still  rare,  and  the  results  are  inconclusive;  either  more  proactive  individuals  

or  more  reactive  ones  may  become  dominant  (Verbeek  et  al.  1996,  Øverli  et  al.  2004,  Korzan  

et  al.  2006,  Fox  et  al.  2009,  Dahlbom  et  al.  2011,  David  et  al.  2011).    

  27  

We  have  tested  the  predictive  power  of  behavioural  responses  in  a  non-­‐social  context  on  the  

establishment  of  social  status  in  male  domestic  fowl  (Gallus  gallus  domesticus).  The  fowl  is  a  

group-­‐living  species  that  readily  forms  social  hierarchies  where  individuals  obtain  clear  social  

roles  (Kruijt  1964).  Despite  the  long  history  of  studies  on  social  hierarchies  in  the  fowl,  traits  

determining   status   are   not   fully   understood.   Ornaments   (e.g.   the   comb,   a   fleshy   red  

ornament  on  the  head),  and  other  morphological  features  (like  body  size)  often  contribute  

to  assessment  of   the  antagonist,  but  do  not   fully  predict   the   social   status  of   an   individual  

(Ligon  et  al.  1990,  Zuk  and  Johnsen  2000,  Parker  et  al.  2002,  Cornwallis  and  Birkhead  2007).  

Our   hypothesis   is   that   there   is   scope   for   also   behavioural   variation   to   explain   variation   in  

establishment  of  social  status  in  the  fowl.  We  therefore  investigated  if  variation  in  behaviour  

in   a   novel   arena   test,   and   aggressive   behaviour   at   the   start   of   a   duel,   could   predict   the  

outcome  of  duels  of  morphologically  matched  males.  Our  expectation  is  that  more  proactive  

or  aggressive  males  have  a  higher  chance  of  becoming  dominant.    

METHODS

Study population and housing

The   study   took   place   during   the   breeding   seasons   (June   -­‐   August)   of   2011   and   2012   at  

Tovetorp  Research  station,  Stockholm  University,  Sweden.  The  population  of  an  old  Swedish  

game  breed  of  fowl  (‘Gammalsvensk  dvärghöna’,  Gallus  gallus  domesticus)  is  kept  in  several  

mixed-­‐sex,  mixed-­‐age   (1-­‐10   years)   groups   under   semi-­‐natural   conditions,   and   are   used   to  

human  handling.  All  males  were  marked  with  numbered  leg  rings  to  facilitate  identification.  

In  order  to  standardise  the  social  position  of  experimental  males,  single  males  were  housed  

together  with   one   female   in   outdoor   aviaries   (3   x   3  meters)   for   4-­‐5   days   before   the   first  

behavioural  test.  Aviaries  were  visually,  but  not  vocally,   isolated  from  other  birds.  This  set-­‐

up  resulted  in  that  all  males  behaved  like  dominant  birds  prior  to  observations  (Parker  and  

Ligon  2002).  The  experiments  followed  ethical  requirements  for  animal  experimentation   in  

Sweden  (Linköping  Ethical  committee,  ethical  permission  number  60-­‐10).  

Personality assays

To   investigate  variation   in  activity  and  explorative  behaviour  among  males,  50  males  were  

tested  singly  in  a  Novel  Arena  test  (NA).  NA  is  a  commonly  used  personality  test  to  measure  

 28  

exploration  and  activity,  and  the  fowl  show  repeatability  in  both  traits  in  similar  tests  (Favati  

et   al.,   unpublished   (paper   I)).   A   large   oval   shaped   arena   of   a   10   x   7   m   fenced   area   in   a  

deciduous   forest  was  divided   into  36  even-­‐sized   subareas  by  a  grid  of   thin  wooden   sticks.  

The  male  was  placed  in  a  cage  of  chicken  wire  connected  to  the  arena  by  a  wire  door.  The  

door  to  the  start  cage  was  immediately  opened,  after  which  the  behaviour  of  the  male  was  

recorded  for  20  minutes.  The  occurrence  of  ‘activity’  (i.e.  movement  of  the  legs  of  the  bird,  

either  by  walking  or  scratching)  was  recorded  every  15s.  The  number  of  subareas  visited  at  

least  once  by  a  male  (between  1-­‐36)  was  used  as  a  measure  of  ‘area  use’,  and  the  latency  to  

visit  at   least  5  subareas  was  used  as  measures  of   ’exploration‘  propensity.  The  limit  of  five  

subareas  was  chosen  in  order  to  obtain  a  continuously  distributed  variable,  and  a  majority  of  

the  males   visited   five   subareas  within   the   time   limit   of   the   experiment.   The   observer   sat  

outside   the   arena,   visible   to   the   male.   The   number   of   territorial   crows   uttered   was   also  

recorded  ('crowing'),  as  was  the  proportion  of  time  a  male  spent  being  vigilant  (‘vigilance’,  

head  above  shoulder  height,  recorded  every  15s.).  At  the  end  of  the  NA,  a  recorded  alarm  

call  of  a  conspecific  was  played-­‐back  using  an   iPhone  connected  to  a  portable   loudspeaker  

placed   next   to   the   arena   (Philips  Mighty  Mini).   Alarm   calls   are   loud   cackling   vocalisations  

typically   uttered   in   response   to   terrestrial   predators,   and   which   flock   mates   react   on   by  

vigilance  (Evans  et  al.  1993).  The  latency  until  the  male  retained  normal  activities  after  the  

call  was  played,  thus  stopped  being  vigilant  and  resumed  feeding  after  the  startle,  was  used  

as  a  measure  of  how  alert  and  wary  the  male  was  ('alertness').  Males  that  did  not  resume  

feeding  within  10  minutes  received  the  maximum  score  of  10  minutes.      

Aggressiveness and social status

To  investigate  whether  variation  in  aggressiveness  affects  establishment  of  social  dominance  

in   the   domestic   fowl,   aggressiveness   was   estimated   during   dyadic   interactions   not   more  

than  one  day  after   the  personality   assays.   Pairs  of  males   (npairs   =   25)  were   simultaneously  

placed  one  meter  from  each  other  in  an  outdoor  aviary  (2  x  3  m)  where  none  of  the  males  

had  previously  been  housed.  The  males  of  each  pair  were  matched  for  comb  size  and  body  

size   in  order  to  minimise  the  influence  of  these  traits  on  the  establishment  of  social  status  

(<10%   difference).   Body   size   and   comb   size   were   estimated   by   tarsus   length   and   body  

weight,  and  comb  length,  respectively.  Males  within  a  pair  had  not  been  housed  together  for  

at  least  2  weeks  prior  to  trials,  reducing  any  effects  earlier  encounters  may  have  had  on  the  

  29  

establishment  of   social   status   (McBride  1958,  Cloutier   et   al.   1995).   The  duels  were   filmed  

using   a   digital   camcorder   (Sony   DCR-­‐VX1000E).   The   agonistic   interaction   between   males  

started  spontaneously  when  the  two  males  of  a  pair  were  placed  in  front  of  each  other.  The  

intensity   of   fowl   fights   typically   ranges   from   aggressive   displays   (raised   hackles,   dropped  

wing   and   ‘waltzing’   movements   (Collias   1943,   Kruijt   1964))   and   surrender   of   one   male  

without  any  physical  attacks,   to  repeated  attacks  with  the   feet  or   the  beak  until  one  male  

retreats.  The  initial  behaviour  (aggressiveness)  of  each  male  was  classified  along  a  four  grade  

scale   as   either   1:   ‘surrending’   (fleeing   away   from   the   other   male),   2:   ‘non-­‐aggressive’  

(straight   body   posture,   no   avoidance   or   attraction   to   the   other   male),   3:   ‘aggressive’  

(crouched   body   posture   and   dropped   wing   or   raised   hackles   (Collias   1943))   or   4:   ‘very  

aggressive’  (directly  –  within  2  seconds  –  approaching  the  other  male).  All  duels  ended  with  

one   of   the   opponents   retreating   and   no   longer   retaliating   further   attacks   from   the  

opponent.  We  used  a  minimum  of  five  occasions  of  avoidance  within  an  hour  by  the  same  

male   to   define   a  male   as   subordinate,   and   the  other  male   as   dominant.  Overt   aggression  

lasted  not  longer  than  a  few  minutes,  and  there  were  no  duels  involving  injuries  other  than  

minor  bleeding  from  the  comb.    

Statistical analyses

To  investigate  whether  behaviour  in  the  novel  arena  test  could  predict  the  outcome  of  the  

duels,  we  compared  a  generalized  linear  model  with  binary  response  containing  all  possible  

explanatory   variables   (activity,   area   use,   exploration,   crowing,   vigilance,   alertness)   with   a  

null  model  containing  no  explanatory  variables  (only  the  intercept),  using  log-­‐likelihood  Χ2-­‐

statistics   (deviance).   To   obtain   only   one   measure   per   pair,   we   used   the   difference   in  

response   between   the   two  males   of   each   pair,   and   randomly   altered   between   taking   the  

dominant   score   minus   the   subordinate   score   and   vice   versa.     The   outcome   of   the   duels  

(dominant  or   subordinate)  was  used  as   response  variable  and  at   the   level  of   the  pair   (n  =  

25).  To  determine  a  final  model,  we  used  bidirectional  stepwise  model  search,  choosing  the  

model  with   the   lowest  AIC  using   generalized   linear  modelling   (Venables   and  Ripley  2002).    

The  fit  of  the  final  model  was  tested  using  the  log-­‐likelihood  Χ2-­‐statistic  for  the  final  model  

compared   to   the  null  model.   To  evaluate   the  predictive  power  of   the  model  we  used   the  

Nagelkerke   r2   (Nagelkerke   1991).   The   strength   of   the   models   was   further   examined   by  

computing  classification  tables  using  the  data  the  models  were  built  on.  The  cut-­‐off  value  to  

 30  

classify  each  males'  social  status  was  set  to  0.5  based  on  the  equal  amount  of  dominant  and  

subordinate  males  (Elliott  and  Woodward  2007).  The  same  approach  as  described  above  was  

used   in  order   to  analyse  whether  behaviour   in  NA  could  predict  aggressiveness  during   the  

first   seconds  of   the  duel,   this   time  with   aggressiveness   as   a   binary   response   variable   (0   =  

non-­‐aggressive,  score  1-­‐2;  1  =  aggressive,  score  3-­‐4).  Whether  aggressiveness  could  predict  

social  dominance  was  analysed  by  a   logistic   regression  with  aggressiveness  as  explanatory  

factor   and   social   dominance   as   response   variable.   Finally,   pairwise   correlations   using  

Pearson’s   product   moment   correlation   were   performed   in   order   to   investigate   the  

relationship  between  all  behavioural  responses  measured.      

In  order  to  achieve  normally  distributed  variables,  the  transformation  √x  was  used  for  area  

use  and  crowing,  log(x)  for  exploration,  and  x0.25  for  alertness,  based  on  visual  inspection  of  

histograms.  These  transformations  were  used  for  all  analyses.  R  version  2.15.1  was  used  for  

all  statistic  analyses  (R  Development  Core  Team  2012).  

RESULTS

A   full  model   containing  all  behavioural   responses  of   the  novel  arena   test   showed   that   the  

responses  could   forecast   the  social  dominance   in  upcoming  duels   (Χ2  =  12.573,  df   =  6,  p   =  

0.050).  We  therefore  proceeded  with  model  selection  which  resulted   in  the  following  final  

model:  social   status  ~  exploration  +  vigilance  +  crowing.   This  model   significantly  predicted  

social   status   (Χ2  =  11.662,  df   =  3,  p   =  0.0086,   r2  =  0.50),   and   the  only   significant   term  was  

exploration;  males  that  more  quickly  explored  the  arena  more  often  won  the  following  duel  

(exploration,  Χ2  =  5.50,  df  =  1,  p  =  0.019;  vigilance,  Χ2  =  2.43,  df  =  1,  p  =  0.12;  crowing,  Χ2  =  

3.16,  df  =  1,  p  =  0.075,  Fig.  1).  This  model  accurately  classified  the  males  in  84%  of  the  cases  

(Table  2).  Behaviour  in  NA  could  not  predict  aggressiveness  at  the  start  of  the  duel  (Χ2  =  7.61,  

df  =  6,  p  =  0.27),  and  this  was  confirmed  by  pairwise  correlations:  no  behaviour  in  NA  had  a  

significant   correlation   with   aggressiveness   (Table   1).   However,   aggressiveness   predicted  

social  dominance:  more  aggressive  males  had  increased  chances  of  becoming  dominant  (Χ2  =  

8.21,  df  =  1,  p  =  0.0042,  r2  =  0.37,  Fig.  2).  The  logistic  model  of  aggression  correctly  classified  

the  status  of  males  in  80%  of  the  cases  (Table  2).  

  31  

DISCUSSION

Socially  dominant  individuals  commonly  enjoy  increased  access  to  resources,  such  as  mating  

partners,   which   typically   results   in   a   positive   relationship   between   social   status   and  

reproductive  success  and  thereby  individual  fitness  (Andersson  1994).  We  here  showed  that  

the  behavioural  type  affected  the  chances  of  obtaining  a  high  socials  status  for  individuals  of  

the  same  apparent  physical  quality.    

No  strong  correlations  were  observed  between  behavioural  responses  observed  in  the  novel  

arena  test,  when  exposed  to  a  startle  and  during  duels,  other  than  the  one  between  activity  

and  exploration.  In  other  words,  we  found  no  support  for  an  overall  behavioural  syndrome  

categorising  individuals  along  a  proactive-­‐reactive  continuum,  which  is  sometimes  found  in  

other  species  (Sih  et  al.  2004a).  Therefore,  we  discuss  each  behavioural  trait  separately.  

Dominant   male   fowl   differ   quantitatively   from   subordinate   males   in   their   behaviour,   for  

example   they   crow   more   (Favati   et   al.   ,   Leonard   and   Horn   1995,   Johnsen   et   al.   2001).  

Crowing   is   an   auditory   display,   which   signals   dominance   and   territoriality,   and   dominant  

males   often   interfere   with   subordinate   males   that   attempts   to   crow   (Collias   et   al.   1964,  

Leonard   and  Horn   1995).   Dominant  males   are   also  more   vigilant   (Pizzari   2003,   Cornwallis  

and  Birkhead  2008),  perhaps  due  to  mate  guarding  (Artiss  and  Martin  1995).  However,  we  

found   no   support   of   pre-­‐existing   differences   between   future   dominant   and   subordinate  

individuals  in  neither  how  much  a  male  crowed,  nor  how  much  time  he  spent  being  vigilant  

in   NA.   The   differences   observed   in   other   studies   (Favati   et   al.   ,   Leonard   and   Horn   1995,  

Johnsen  et  al.  2001,  Pizzari  2003,  Cornwallis  and  Birkhead  2008)  therefore  primarily  seem  to  

be  an  effect  of  the  current  social  position  rather  than  pre-­‐existing  differences  in  behavioural  

type  (Favati  et  al.  ,  Cornwallis  and  Birkhead  2008).  Among  all  behavioural  traits  observed  in  

the  novel  arena  test,   including  exposure  to  a  startle,  only  exploration  seemed  to  have  any  

substantial   relationship   to   future   social   status,   as   more   explorative   males   more   often  

became   dominant.   Exploration   was   strongly   correlated   to   activity   and   the   number   of  

subareas  visited,  and   the   results   suggest   that   this  vigorousness  brought  advantages   to   the  

duel  situation,  although  not  through  a  direct  relationship  with  aggressiveness.  This  adds  to  

the   general   pattern   of   more   proactive   individuals   being   found   in   dominant   positions,  

although   only   a   few   have   investigated   the   relationship   between   exploration   and   social  

 32  

dominance,  and  in  a  some  cases  with  opposite  results  (Verbeek  et  al.  1996,  Dingemanse  and  

de  Goede  2004,  Fox  et  al.  2009,  David  et  al.  2011).      

That  more  aggressive  individuals  win  more  fights  has  been  demonstrated  in  earlier  studies  of  

various   species   (e.g.   (Verbeek   et   al.   1996))   including   the  domestic   fowl,  where   individuals  

that  initiate  the  first  attack  more  often  also  win  the  fight  (females,  Ligon  et  al.  1990,  males,  

Cloutier   and  Newberry   2000).   Aggression   is   however   sometimes   considered   a   property   of  

the   interaction   between   individuals,   in   which   case   the   individual   aggressive   response  

depends  on  the  actions  of  the  opponent  (Francis  1988).  For   instance,  whether  an  attack   is  

initiated  or  not   is  not  a  purely   individual  decision,  but  also  depends  on   the  actions  of   the  

opponent.   Alternatively,   as   adopted   in   the   current   study,   one   can   attempt   to   estimate  

individual   aggressiveness   and   distinguish   it   from   social   dominance.   Thus,   individual  

aggressiveness  can  be  estimated  by  the  very   initial  reaction  of  an   individual  when  meeting  

an   opponent.   By   basing   our   measure   of   aggressiveness   on   how   the   males   react   to   the  

fighting  situation  during   the  very   first   seconds  of   the   interaction,   it   seems  unlikely   that  an  

evaluation  of  the  opponent  already  has  taken  place.  Using  this  approach,  we  found  that  an  

initial   aggressive   position   forecasts   the   outcome   of   the   duel   in   male   fowl,   which   has  

previously  been  shown  only  in  female  fowl  (Foreman  and  Allee  1959,  Wilson  1974).    

When  males   differed   in   aggressiveness  within   a   pair,   the  male  with  higher   aggressiveness  

scores  almost  always  won  the  fight  (Figure  2).  However,  in  around  half  the  cases  both  males  

initially  adopted  an  aggressive  body  posture   (i.e.   received   the   same  aggressiveness   score),  

which  decreases   the  strength  of   the  overall  predictability.  Despite   this,  aggressiveness   still  

appeared  as  a  useful  predictor  of  status,  as  it  was  used  to  correctly  predict  the  outcome  in  

80  %  of  the  duels.  Explorative  behaviour  comes  forth  as  an  equally  strong  predictor  of  status  

(Table  2).  Overall,  our  results  show  that  when  combatants  were  matched  for  morphological  

characters,  behavioural  traits  did  play  an  important  role  in  the  establishment  of  social  status.  

We   targeted   aggressiveness   and   exploration   as   the   prior   attributes,   or   personality   traits,  

most  useful   for  prediction  of   a  dominant   social   position.  Over   the   last  decade,   reports  on  

fitness   effects   of   behavioural   types   have   accumulated;   not   least   studies   showing   that  

personality  affects  reproductive  success  (Dingemanse  and  Reale  2005,  Smith  and  Blumstein  

2008).  Since  dominance   is   important   for   sexual   success   in  male   fowl   (McBride  et  al.  1969,  

  33  

Collias   and   Collias   1996,   Pizzari   and   Birkhead   2001),   our   results   suggest   that   variation   in  

personalities  in  male  fowl  have  fitness  consequences  via  the  establishment  of  social  status.  

ACKNOWLEDGEMENTS    

We  wish  to  thank  A.  Hennyey,  D.  Molin  and  L.  Neuman  for  field  assistance,  and  N.  Andbjer  

for  game  keeping.      

 34  

Tables

Table  1.  The  relationship  between  behavioural  responses  in  behavioural  assays  and  initial  aggressiveness  

in  duels,  of  male  fowl.    

    Exploration     Area  use   Activity   Crowing   Vigilance   Alertness   Aggressiveness  Exploration     -­‐  

           Area  use   -­‐0.70*   -­‐            Activity   -­‐0.51*   0.78*   -­‐  

       Crowing   -­‐0.21   0.14   -­‐0.073   -­‐        Vigilance   -­‐0.34   0.25   0.10   0.24   -­‐  

   Alertness   -­‐0.153   -­‐0.14   -­‐0.089   0.018   0.381   -­‐    Aggressiveness   -­‐0.038   -­‐0.048   -­‐0.021   -­‐0.43   0.016   -­‐0.055   -­‐  

Pearson’s  correlation  coefficients  (r)  are  shown.  *  denotes  correlations  that  remained  significant  at  the  p  <  

0.05  level  after  sequential  Bon  Ferroni  correction.  

  35  

Table  2.  Classification  table  comparing  observed  dominance  status  with  dominance  status  predicted  by  

final  logistic  models.    

 Observed   Predicted   Percentage  

   Sub   Dom   correct  

Novel  arena   Sub   10   2   0.83     Dom   2   11   0.85  

       total  0.84  

Aggressiveness   Sub   7   5   0.58  

 Dom   0   13   1.00  

       total  0.80  

Dominance status of males (subordinate, 'Sub', and dominant, 'Dom') was successfully classified by the final

logistic regression model of behavioural responses in the novel arena test in 84% of the cases, and in 80% of the

cases by the logistic model of aggressiveness during the start of the duel (in bold).

 36  

 

Figure  1.  Differences  in  behavioural  response  in  behavioural  assays  between  future  dominant  and  subordinate  

male  fowl.  Males  that  in  a  later  duel  became  dominant  (filled  dots)  (a)  were  more  explorative  but  (b)  were  not  

more  active,   (c)  did  not  have  a   larger  area  use,   (d)  did  not  crow  more,  and   (e)  were  not  more  vigilant  or   (f)  

more  alert  compared  to  subordinate  males  (open  dots).  Mean  values  ±  SE  are  given.  *  =  p  <  0.05.  

●

●

0

2

4

6

8

10La

tenc

y to

exp

lore

5 su

bare

as (m

in)

Dom Sub

(a)*

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10

20

30

40

Activ

ity (%

of t

ime)

Dom Sub

(b)

●

●

0

5

10

15

20

25

30

No.

of s

ubar

eas

visi

ted

Dom Sub

(c)

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10

15

20

25

30

Num

ber o

f cro

ws

Dom Sub

(d)

●

●

50

60

70

80

90

100

Vigi

lanc

e (%

of t

ime)

Dom Sub

(e)

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●

0

40

80

120

160

Vigi

lanc

e af

ter s

tartl

e (s

)

Dom Sub

(f)

  37  

 

Figure   2.   The   distribution   of  male   fowl   duels   with   respect   to   the   difference   in   aggressiveness   between   the  

contestants.   The  winning,   dominant  male   either   had   a   higher   aggressiveness   score   compared   to   the   losing,  

subordinate   part   (Dom>Sub,   black   column),   a   lower   score   (Sub<Dom,   white   column)   or   the   same  

aggressiveness  score   (Dom=Sub,  grey  column).  When  threat  score  differed  between  the  two  males  of  a  pair,  

the  male  with  the  higher  aggressiveness  score  more  often  won  (12  cases  vs  1  case).    

# of

due

ls

0

2

4

6

8

10

12

Dom>Sub Sub>Dom Dom=SubDifference in aggressiveness

 38  

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