animal behaviour advantages no 1

ANIMAL BEHAVIOUR: ADVANTAGES AND DISADVANTAGES NO.1

Kevin Brewer ISBN: 978-1-904542-36-0

Animal Behaviour: Advantages and Disadvantages No.1; Kevin Brewer; 2008 2

This document is produced under two principles: 1. All work is sourced to the original authors. The images are all available in the public domain (most from http://commons.wikimedia.org/wiki/Main_Page ). You are free to use this document, but, please, quote the s ource (Kevin Brewer 2008) and do not claim it as you own work. This work is licensed under the Creative Commons Attribution (by) 3.0 License. To view a copy of thi s license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ or, send a letter to Creative Commons, 171 2nd Street, Suite 300, San Francisco, California, 9 4105, USA. 2. Details of the author are included so that the l evel of expertise of the writer can be assessed. This co mpares to documents which are not named and it is not poss ible to tell if the writer has any knowledge about their subject. Kevin Brewer BSocSc, MSc ( http://kmbpsychology.jottit.com/ ) An independent academic psychologist, based in Engl and, who has written extensively on different areas of psychology with an emphasis on the critical stance towards traditional ideas. Orsett Psychological Services, PO Box 179, Grays, Essex RM16 3EW UK [email protected]


CONTENTS Page Number 1. Advantages and Disadvantages of Animal Migration 4 2. Advantages and Disadvantages of Ambush Hunting 19 3. Advantages and Disadvantages of Caching Behaviour 25 4. Advantages and Disadvantages of Territoriality 35 5. Advantages and Disadvantages of Delayed Breeding in Birds 47


1. ADVANTAGES AND DISADVANTAGES OF ANIMAL MIGRATION Migration refers to "regular movements between areas uninhabited at different times of the year" (Cocker 1993) or "long-distance travel, usually with a return, to specific locations" (Grier and Burk 1997). Migration is triggered by seasonal changes in weather, air temperature or day length, or changing food supply. For example, wildebeest move towards rain i n the dry season. Some animals move from one food source to another, while others migrate to particular breedin g areas. Most interest relates to bird migration, but o ther animals also migrate through water or over land (ta ble 1.1). It has been estimated that 5 000 million bird s migrate southwards across the Mediterranean area to trans-Saharan Africa each year (Moreau 1972). COMMON NAME SCIENTIFIC NAME WHERE Caribou Rangifer tarandus North America Wildebeest Connochaetes taurinus Africa Saiga antelope Saiga tatarica (figure 1.1) Central Asia Mongolian gazelle Procapra gutturosa Mongolia White-tailed deer Odocoileus virginianus North America Table 1.1 - Examples of migrating mammals.

(Source: US Federal Government)

Figure 1.1 - Saiga antelope.


There are advantages and disadvantages to migr ation generally (table 1.2) as well as in relation to mig ration for breeding or migration for food (table 1.3). ADVANTAGES 1. Return to specialist site for breeding that does not need all year round food supply, and often no (or few) predators. 2. Move to where food/prey available when not breed ing, particularly with young (ie: maximise feeding opportunity). 3. Stationary can mean increased predator risk. 4. Constant temperature conditions: escape bad weat her and lower temperatures (and greater risk of death), especiall y to give birth. 5. Able to have specialist breeding site (eg: no pr edators) and another site for feeding. 6. Flexible strategy - some members of the species can migrate and others not depending on where live. 7. Stationary animals risk exhausting food supply u sing it all year round, particularly if competition from other speci es. 8. Opportunity for different members of the species to meet, and greater breeding variety (eg: storks from western a nd eastern Europe; figure 1.2). 9. Ideal when specialist food required because the earth's resources are not evenly distributed. Most land mass and shal low seawater in the northern hemisphere; eg: Arctic tern (Sterna pa radisea) feed on whitebait in shallow waters, and European swallow ( Hirundo rustica) on flying insects on land (Whitfield et al 1981). 10. Birds migrating at night usually safe from pred ators as few day-time birds of prey adapt to night-time hunting. DISADVANTAGES 1. Large amount of energy required to travel long d istances. 2. Problems and risks of navigation. 3. Risk of forgetting sites or not being able to fi nd again. 4. Leave home territory empty allowing for invaders , and then fights on returning. 5. Risk at temporary stopovers from lack of local k nowledge about predators. 6. Vulnerable to weather changes or poor conditions in one year. 7. Many decisions required including optimal fuel l oad and optimal time of departure. 8. Other risks like the change from salt to freshwa ter or vice versa for some fish.


9. Evolutionary maladaptive behaviour in some cases ; eg: green turtles (Chelonia mydas)(figure 1.3) feed on easter n coast of South America but breed on Ascension Island (south Atlant ic); adequate breeding sites nearer to feeding areas (Whitfield e t al 1981). 10. Risks of night-time migration if animals normal ly active in day-time (eg: bat predation of birds). Table 1.2 - Advantages and disadvantages of migrati on.

(Source: Bamse)

Figure 1.2 - Migration routes of white stork.

(Source: US Fish and Wildlife Service)

Figure 1.3 - Green turtle.


Migration for breeding - 1, 5, 8 Migration for feeding - 2, 7, 9 Table 1.3 - Specific advantages in table 1.2 depend ing upon type of migration. DISTANCE The length of migration varies from 1-2 metres per day by zooplankton to thousands of miles by some bi rds. For example, an Arctic tern, which was ringed, was found to fly from Russia to the Antarctic (9000 miles)(Gr ier and Burk 1992)(figure 1.4). Monarch butterflies fly up to 2000 miles between USA/Canada and Mexico.

(Source: Andreas Trepte)

Figure 1.4 - Migration routes of Arctic tern. Studies of ringed populations of birds (figure 1.5) found in different places is one way to study the migration distances. For example, Black-browed albatrosses (Diomedea melanophris) from the Falklan d Islands (south Atlantic) have been discovered in So uth America mainly, but ringed birds from South Georgia (south Atlantic) mainly found in southern Africa (q uoted in Cramp and Simmons 1977).


(Source: Julio Reis)

Figure 1.5 - The ringing process by "Cruzinha" (national bird ringing authority) in Portugal. There are cases from displacement experiments of albatrosses migrating very long distances. Displace ment experiments involve taking birds to a point of rele ase that is different to their normal migration point, and to see if they return to the original home. The birds are ringed so records can be kept. For example, Laysan albatrosses returned 5200km in 10-12 days from the west coast of the USA to Midway Island (Pacific), or fro m the Philippines to Midway Island (6500km taking one mon th) (Alerstam 1993). At the other extreme, the common toad (Bufo bu fo) moves a few hundred yards from vegetation to pond t o spawn. VARIATIONS IN PATTERNS Within some species certain individuals migrat e and others do not (eg: blackbirds found further north d o). There can also be differences between the sexes (eg : chaffinch males more migratory than females).


Robins (Erithacus rubecula)(figure 1.6) are par tially migratory. This means that some "races" and some bi rds within those "races" migrate, while others are sede ntary. The robins of Britain and Ireland that do migrate g o South South-West to Iberia (Spain/Portugal). This o ccurs from September-October through to March-April (Rose laar 1988). Most migration occurs at night (Elphick 1995 ). There are sex differences in migration among r obins. Males are more sedentary than females generally. Ta ble 1.4 lists the estimates of the number of robins who were sedentary in four different studies. STUDY MALE FEMALE Enniskillen (1926) 75 36 Devon (1965) 70 33 Cambridge (1984) 77 30 Oxford (1988) 69 3 (After Harper 1988)

Table 1.4 - Percentage of robins who are sedentary by sex in four different studies.

(Source: Ramin Nakisa)

Figure 1.6 - Robin. Whether the birds migrate or not depends on th e local conditions, like unpredictable winters. There are three stages to the evolution of migratory behaviou r in a


species (Gill 1995): i) Partial migration - Some of the species migrates while others do not; ii) Division - Species separated into two clear groupings: migratory and non-migratory; iii) Natural selection leads to the elimination of one group. As a species, robins are probably between stag es 1 and 2 above. Birds build up their body mass in late summer to coincide with the "zugunruhe" behaviour (migratory restlessness) (Biebach 1983). Experiments with robins in steel cages with ma gnets attached have found that they are influenced by mag netic cues (Merkel and Wiltschko 1965 quoted in Gill 1995 ). INSTINCT AND LEARNING Though certain animals may have a "migratory instinct", it is modified with learning in terms of how often to migrate, and the direction travelled. Perdeck (1958) took starlings, which usually migrated from northern Europe in a south-west direc tion to southern Europe, to Switzerland for release. Juv enile birds flew south-west, but adults adjusted and flew to their normal destination. MIGRATION DECISIONS Migration involves a number of decisions to pr oduce the optimal mating strategy: 1. Optimal fuel load How much stored fat, protein and food stored i n the digestive tract before beginning. Too much slows th e animal down and reduces the ability to escape chasi ng predators. Too little increases the risk of starvat ion during the migration. A range equation gives "the potential migration distance in relation to fuel lo ad" (Hedenstrom 2003a). The ideal for birds should be short steps and small fuel loads compared to large distances and large fu el loads (Alerstam 2001).


2. Number and duration of stopovers (optimal stopov er duration) Each stopover risks local predators and taking longer to reach destination against the need for fu el. Taking longer may mean missing the best breeding si tes or opportunities. Hedenstrom (2003b) calculated the proportion o f time spent on travelling against refuelling as 1:3 in ru nning migrates. In other words, three times as long feedi ng as travelling. 3. Speed of movement Moving faster uses more energy but arrives qui cker. 4. Chosen or enforced detours Whether to go directly from A to B or via anot her place (eg: feeding site)(chosen detour). While enfo rced detours are barriers for land migrating animals, li ke rivers or mountains, and poor weather conditions fo r birds (eg: blown off course). 5. Optimal time of departure Before the weather changes negatively or food supply exhausted here, and arrive when food supply best at destination. Birds are known to leave stopover site s when winds are favourable (Akesson and Hendestrom 2002). KNOWING WHEN TO MIGRATE Migration is about moving to the right place a t the right time. Birds seem to have circannual (annual) biological clocks which trigger the migratory restlessness (Zugunruhe) and put on weight beforeha nd (Elphick 1995). The biological clock, probably linked to the pineal gland in the brain and connect ed to the visual system, responds to changes in light and darkness with the seasons. But there is also an endogenous biological clo ck which works irrelevant of changes in the environmen t. Gwinner (1986) kept wild birds in special cages for over three years. The environment was controlled so that there was always 12 hours of daylight and 12 hours of dar kness. Thus the removal of external cues to migration. But the birds showed the migratory restlessness at the appropriate time of the year still. However, the Wandering albatross (Diomedea exu lans)


breeds biennial, and so migrates to the breeding si te every other year; even less frequently in some case s. How does the biological clock work in this situation? MECHANISMS USED TO NAVIGATE One area of major interest in relation to migr ation is how the animals know where to go (migratory orientation systems). Birds, which travel vast dist ances, are of particular interest, and the cues they are u sing. Table 1.5 shows the different cues that animals use to navigate. 1. Sun compass - movement of sun; angle of sun; pol arised light (pattern of light based on sun's position and refle ction on water). 2. Geomagnetic compass - sensitivity to magnetic No rth and the earth's magnetic field. 3. Star compass or position of moon. 4. Other visual cues - patterns of waves; cloud pat terns; landmarks. 5. Smell. 6. Sound. 7. Electric. Table 1.5 - Different cues used by animals to navig ate. The use of a geomagnetic compass by birds is h otly debated. The geomagnetic declination is the differe nce between the North Pole and "magnetic North", and it varies based on global position (Thorup et al 2006) . The development of satellite-based radioteleme try has meant that birds fitted with small transmitters can be tracked during their migration in free-flying st udies. For example, Thorup et al (2006) tracked the route taken by 25 peregrine falcons (Falco peregrinus)(figure 1 .7) in the autumn movement between North and South America , and seven honey buzzards (Pernis apivorus) and thirteen ospreys (Pandion haliaetus) between Europe and Afri ca. The researchers wanted to see if the birds fol lowed a geographical compass (direct route from home to destination) or a geomagnetic compass (curved path) . For example, in North America in autumn, birds followin g a fixed magnetic course will curve anti-clockwise (so uth to east) when migrating south-east in western North Am erica and clockwise (south to west) when flying south-wes t in the east.


(Source: US Fish and Wildlife Service) Figure 1.7 - Peregrine falcon eating on US Fish and Wildlife Service boat. The flight direction for all three species wer e closer to a predicted constant geographical compass . This suggested that the birds were flying directly towar ds their destination (aided by celestial cues like sta rs during night flight) and not using magnetic cues. However, it is quite probable that birds use a selection of orientation cues to establish the dire ction of migration. For example, geomagnetic cues become important when there is cloud cover. Thorup et al ( 2006) were also pragmatic in admitting that different spe cies of birds may use different cues. Other researchers use different methods to stu dy this same behaviour. Cue-conflict experiments study orientation cues in laboratory-based surroundings. A typical example (Akesson et al 2002) involved 36 ju venile white-crowned sparrows (Zonotrichia leucophrys gamb ellii) captured in northern Canada. They usually migrate s outh-east to southern USA for the winter. The birds were kept in cages surrounded by magnetic coils that shifted the magnetic field by ninety degrees. If the birds use celestial cues to migrate at night, they will be unaffected by the shift in magnetic fi eld, whereas if magnetic cues are used they will be. The top


of the cages had Emlen funnels (Emlen and Emlen 196 6). These are funnels through which the birds can see t he sky, but it is too small for them to fly through. T he direction the bird is trying to fly is recorded on Tipp-Ex paper which lined the funnel. The sparrows showed that they were influenced by the shifted magnetic field, and so must have been using magnetic cues. However, released birds were able to recalibrate quickly using celestial cues. Free-flying studies have advantages and disadvantages in relation to laboratory studies whi ch artificially change the magnetic fields and orienta tions in cages (table 1.6). FREE-FLYING STUDIES Advantages 1. Studying birds in their natural habitat. 2. Study over larger distances than laboratory stud ies. 3. Aided by development of modern technology which overcomes the problem of observers missing behaviour. 4. Little interference of bird's behaviour by resea rchers. 5. Gives fuller picture of behaviour than in short experiments. Disadvantages 1. Birds fitted with tracking devices which may cha nge their behaviour; eg: radio-transmitters produce very weak magnetic field. 2. Expensive, particularly if bird dies or migratio n studied not typical (like extreme weather). 3. Tend not to have control group. 4. Lack of control of variables. 5. Not possible to establish causality. LABORATORY EXPERIMENTS Advantages 1. Control over birds and variables studied. 2. Possible to establish cause and effect. 3. Can have multiple conditions each changing a dif ferent variable as well as a control group. 4. Birds watched (or video-recorded) all the time a nd so unlikely to miss changes in behaviour. 5. Replication possible.


Disadvantages 1. Artificial conditions. 2. Whether birds affected by capture and captivity. 3. Whether birds bred in captivity are typical of t he species. 4. Behaviour measured for limited period only. 5. Narrowness of independent and dependent variable s. Table 1.6 - Advantages and disadvantages of free-fl ying and laboratory studies of migration orientation. RISK OF PREDATORS Animals (particularly birds) are especially vulnerable to predators at temporary stopovers eith er from lack of knowledge of local predators or preoccupation with large food intake. Young birds on their first migration or experi enced birds affected by poor weather conditions stop at s ites never visited before and encounter new types of predators. There is limited time during such stopov ers to gain local information about the risk because of th e demands of "refuelling" (Cimprich et al 2005). Does this mean that birds change their behavio ur during migration? Are they willing to accept greate r risks from predators during temporary stopovers bec ause of the need for food? Research by Cimprich et al (2 005) suggested that this is not necessarily the case and predator avoidance remains just as important during migration as at home. Cimprich et al (2005) used observation and experiment to investigate the behaviour of blue-gre y gnatcatchers (Polioptila caerulea)(figure 1.8) and American redstarts (Septophaga ruticilla) on tempor ary stopovers at Bon Secour National Wildlife Refuge on the coast of Alabama, USA. During the observation part of the research, t he behaviour of these birds in response to the appeara nce of a flying predator (sharp-shinned hawk; Accipter str iatus) was measured. In the experiment part, the researche rs simulated a gliding hawk using a balsa wood model.


(Source: Albuttlee)

Figure 1.8 - Blue-grey gnatcatcher. The appearance of a hawk (real or model) cause d the birds to move deeper into the shrubs (ie: out of si ght), and to reduce movement (birds of prey attracted by movement). When there was no risk of hawks, most of the birds were on the edge of the shrubs moving rapidly from perch to perch. With a high risk of hawks, the bird s moved over 40cms into the shrubs, and changed perch less than once per minute. The experiment produced simil ar data (table 1.7). The birds responded to predators in their normal way (hiding and/or freezing) despite t he negative impact upon amount of food gained. BEF ORE AFTER Median depth into shrubs (cms) 8 18 Mean movement rate (perch changes/min) 30 20 (After Cimprich et al 2005)

Table 1.7 - Blue-grey gnatcatchers' behaviour in re sponse to model hawk. As well as the risk of predation at stopovers, there is also that risk during the movement of migration. For example, Ibanez et al (2001) reported evidence that greater noctule bats (Nyctalus lasiopterus) were capturing nocturnal migrating birds in flight. Based on bat dropping analysis from two region s of


Spain, the researchers found bird remains in the migration periods, March-May and August-November, b ut not during the rest of the year. REFERENCES Akesson, S & Hedenstrom, A (2000) Wind selecti vity of migratory flight departures in birds Behavioural Ecology and Sociobiology 47, 140-144 Akesson, S et al (2002) Avian orientation: Eff ects of cue-conflict experiments with young migratory songbirds in the high Arctic Animal Behaviour 64, 469-475 Alerstam, T (1993) Bird Migration Cambridge: Cambridge University Press Alerstam, T (2001) Detours in bird migration J ournal of Theoretical Biology 209, 319-331 Biebuch, H (1983) Genetic determination of par tial migration in European robin (Erithacus rubecula) Au k 100, 601-606 Cimprich, D.A et al (2005) Passerine migrants respond to variation in predation risk during stopo ver Animal Behaviour 69, 1173-1179 Cocker, J (1993) The migratory and navigationa l behaviour of birds Psychology Teaching December, 2-12 Cramp, S & Simmons, K (1977) Handbook of the B irds of Europe, Middle East and North Africa: Volume 1 - Ostrich to Ducks Oxford: Oxford University Elphick, J (1995) (ed) Atlas of Bird Migration London: Collins Emlen, S.T & Emlen, J.T (1966) A technique for recording migratory orientation of captive birds Au k 83, 361-367 Gill, F (1995) Ornithology (2nd ed) New York: WH Freeman Grier, J.W & Burk, T (1992) Biology of Animal Behaviour Dubuque, IO: W.C.Brown Gwinner, E (1986) Circadian rhythm in the cont rol of avian rhythms Advances in the Study of Behaviour 16, 191-228


Harper, D (1988) Erithacus rubecula Robin: Fie ld characteristics. In Cramp, S (ed) Handbook of the B irds of Europe, the Middle East and North Africa Vol V Oxford: Oxford University Press Hedenstrom, A (2003a) Optimal migration strate gies in animals that run: A range equation and its consequences Animal Behaviour 66, 631-636 Hedenstrom, A (2003b) Scaling migration speed in animals that run, swim and fly Journal of Zoology 259, 155-160 Ibanez, C et al (2001) Bat predation on noctur nally migrating birds Proceedings of the National Academy of Sciences, USA 98, 17, 9700-9702 Moreau, R.E (1972) The Palaearctic-African Bir d Migration Systems London: Academic Press Perdeck, A.C (1958) Two types of orientation i n migrating starlings, Sturmus vulgaris L., and chaffinches, Fringella coelbs L., as revealed by displacement experiments Ardea 46, 1-37 Roselaar, C (1988) Erithacus rubecula Robin: Breeding. In Cramp, S (ed) Handbook of the Birds of Europe, the Middle East and North Africa Vol V Oxford: Oxford University Press Thorup, K et al (2006) Do migratory flight pat hs of raptors follow constant geographical or geomagnetic courses? Animal Behaviour 72, 875-880 Whitfield, P et al (1981) The Rhythms of Life London: Marshall Useful Websites * MIGRATE ( http://www.migrate.ou.edu/ ) open access abstracts on: � white-crowned sparrows and migration

http://www.migrate.ou.edu/pubwiki/index.php/White-crowned_Sparrow_%28Zonotrichia_leucophrys%29_Papers

� American redstarts and migration

http://www.migrate.ou.edu/pubwiki/index.php/America n_Redstart_%28Setophaga_Ruticilla%29_Papers

* BBC project "World on the Move" http://www.bbc.co.uk/radio4/worldonthemove/


2. ADVANTAGES AND DISADVANTAGES OF AMBUSH HUNTING FOR ANIMALS Predators seek prey in different ways. The mos t obvious is the chase. But some predators take a completely different approach, and use "sit-and-wai t" foraging or ambush hunting. This means that the pre dator picks a spot and waits, sometimes for a long period , for the prey to come to them. There are ambush hunters throughout the animal kingdom (table 2.1). Many snakes Many spiders and some other insects Crocodiles and alligators (partly) Some lizards and reptiles (eg: tuatura; Sphenodon punctatus; picture: http://www.bbc.co.uk/nature/wildfacts/factfiles/305 2.shtml ) Few birds (eg: shrike; Laniidae; picture: http://www.montereybay.com/creagrus/shrikes.html ) In sea (eg: monkfish; Lophius upsicephalus. Pacific angel shark; Squatina californica. Anglerfish; Lophiiformes) Table 2.1 - Some examples of ambush hunters. There are advantages and disadvantages of ambu sh hunting (table 2.2), particularly in comparison wit h chasing prey. ADVANTAGES 1. Uses little energy, and much less than chases. 2. Works where prey have predictable habits, like u sing the same routes. 3. Good way to get prey within reach of weapons - e g: teeth (crocodile), poison (snake). 4. Avoids the risk of prey fighting back (and of in jury) if ambush is swift and effective. 5. Best where prey moves around or are geographical ly dispersed. 6. Catch prey when off-guard or not expecting attac k - eg: spider's web and flying insects. 7. Most effective when predator has no natural enem ies. 8. Best when animal does not need to feed too often .


9. It is a strategy than can be used as well as oth ers like chasing the prey. 10. Effective strategy for well-camouflaged animals . 11. Disguises the number of predators competing for food, and risk of fights. DISADVANTAGES 1. Risk that prey will not come or not right type o f prey, and thus starvation. 2. If limited number of prey come, predator must ha ve high success rate or risk of starvation. 3. Risk of becoming prey themselves if stationary f or long periods. 4. Not effective if spotted by prey; thus importanc e of camouflage. 5. Not effective if prey learns to avoid ambush sit es, particularly if predator always uses same sites. 6. Waste of limited resources if ambush unsuccessfu l - eg: snake's poison. 7. If prey are unpredictable means must be alert at all times which limits opportunity for sleep. 8. Risky strategy for animals with high calorie nee ds. 9. Depends on prey being mobile. 10. Too many prey can distract predator for individ ual kill. 11. Lower capture rates than active hunters of same species (eg: lizards; Anderson and Karasov 1981). Table 2.2 - Advantages and disadvantages of ambush hunting for animals. The best ambush hunters will be camouflaged an d attack very quickly. Crypsis is camouflage where th e animal shows visual resemblance to some part of the environment, like crab spiders (Thomisidae) that as sume the same colour as flowers which deceives landing i nsects (Thery and Casas 2002). Pacific angel sharks (Squatina californica) hi des on the sea floor partly covered in soft substrata as w ell as its crypsis. The duration of an attack was measured at 30-100 milliseconds (Fouts and Nelson 1999). Within the same group of animals active and am bush hunting can evolve. Cooper and Whiting (2000) colle cted data on skinks (lizards) in southern Africa (table 2.3).


ACTIVE HUNTERS � More energy used � Higher capture rate � Greater stamina and greater average speed (eg: 0.03 m/s) � Search in wider area per unit time � Higher proportion of time spent moving (PTM)(eg: 0. 49) and higher

number of movements per minute (MPM)(eg: 1.6) � More vulnerable to ambush predators � Examples: Mabuya sulcata (figure 2.1), Mabuya varie gata AMBUSH HUNTERS � Less energy used � Lower capture rate � Greater sprint speed (eg: 0.2 m/s vs 0.008 m/s) but lower average

speed (eg: 0.003 m/s) � Limited search area � Lower PTM (eg: 0.03) and lower MPM (eg: 0.3) � More vulnerable to active hunters � Examples: Mabuya acutilabris, Mabuya spilogaster Table 2.3 - Comparison between active and ambush hu nters among skinks.

(Source: Hans Hillewaert)

Figure 2.1 - Mabuya sulcata.


The strategy of ambush or active hunter also d epends upon the risk to the predator from their predators (eg: jumping spiders: http://www.bgu.ac.il/life/Faculty/Bouskila/when.htm l ). AMBUSH SITE SELECTION The choice of ambush site is very important fo r "sit-and-wait" foragers. Successful ambush sites mu st have certain characteristics (Shine and Sun 2002): i) Site visited frequently and/or in large numbers by prey; ii) Possible for predator to hide - ie: opportunity for camouflage/evade detection; iii) Predator can detect prey immediately on arriva l. This is important if the prey only visit the ambush site briefly; iv) Allows for prey capture. The prey needs to come within the striking distance of the predator. These characteristics may vary in importance depending upon the availability of prey. In the cas e of scarcity, success in finding prey is paramount. Whe reas if the prey are abundant but hard to catch, ambush factors related to capture become most important. Sine and Sun (2002) investigated the site choi ce of one type of pit-viper (Gloydius shedaoensis) in amb ushing migrating birds that land on branches. The study to ok place on Shedao island in north-eastern China, whic h lies on major migratory bird routes, in May 2000. The sn akes only feed on twice-yearly migrating birds, which ca n be a risky strategy (table 2.4). ADVANTAGES 1. High availability of prey twice a year. 2. Birds tired and less wary of predators. 3. Birds not familiar with area and with predators. DISADVANTAGES 1. Risk of no food if migration patterns change (eg : storm blows birds off course). 2. Birds may learn to be wary of snakes' behaviour and change their behaviour.


3. Snakes shut down in between migrations and this involves risks. Table 2.4 - Advantages and disadvantages of pit-vip er strategy of waiting for migrating birds. One hundred and forty-nine snakes were observe d to discover the choice of ambush site on a tree. One h undred and twenty-seven trees were chosen, and the snakes showed preferences for their ambush sites as follows: � To perch in trees on the edge (rather than in the

middle) of thickets or in isolated trees; � Branches facing outward; � Branches lower to the ground. Nearly two-thirds of the

snakes were found on branches 0.5 metres above the ground, and less than 10% 1.5 metres or more above the ground. The majority of the prey observed (564 bird perching events) preferred outward facing branches, and branches less than 1 metre above the ground. This follows criteria (i) above for a successful ambush site;

� Diameter and angle of branch that allowed snake

stability to strike (criteria iv above); � Cool backgrounds which allowed a contrast for the

snakes to use their heat-sensitive facial pits to s pot birds (criteria iii above). Outward facing branches have this.

The branches chosen also allowed camouflage as the snake's body colour and scalation were a visual mat ch to the tree's appearance (criteria ii above). The researchers admitted that "we often failed to see p it-vipers in ambush poses until we had approached them far more closely than we desired". BEING SPOTTED BY PREY Ambush hunting is only successful if the prey does not spot the ambusher. Weislo and Schatz (2003) loo ked at the evasive action taken by female sweat bees (Lasioglossum umbripenne) when detecting ants (Ecta tomma ruidum) waiting in ambush near their nest in Panama . The bees nest in mounds in the soil, and the ants, that are twice as big, wait for returning bees and lunge at them. The ants cannot enter the nest because they are too big. The researchers placed different stimuli at th e nest entrance:


� A dead ant (either with or without its natural smel l) � A black cardboard rectangle (the size of an ant) � A black cardboard square (the size of an ant) � No stimulus � Live ant When there was no stimulus by the nest, the ma jority of bees (85.5%) flew directly into the nest ("appro ach"). When the bees detected an ambusher they changed the ir behaviour ("approach and withdraw"). This included re-approaching the nest from the opposite side (54% of times when live ant present), zigzagging flights, or land ing and walking into the nest. Sometimes the ant was still able to capture th e bee, and, on other occasions, the ant was distracted by other returning bees. "Flexibility in nest entering-exiti ng behaviour of L.umbripenne, in the face of flexible hunting strategies by E.ruidum.. illustrates the dy namics of a complex predator-prey relationship.." (p187). The bees did not change their behaviour in the presence of the cardboard models which suggested th at they visually detect ants. REFERENCES Anderson, R.A & Karasov, W.H (1981) Contrasts in energy intake and expenditure in sit-and-wait and w idely foraging lizards Oecologia 49, 67-72 Cooper, W.E & Whiting, M.J (2000) Ambush and a ctive foraging modes both occur in the Scincid Genus Mabu ya Copeia 1, 112-118 Fouts, W.R & Nelson, D.R (1999) Prey capture b y the Pacific angel shark, Squatina californica: Visually mediated strikes and ambush-site characteristics Co peia 2, 304-312 Shine, R & Sun, L-X (2002) Arboreal ambush sit e selection by pit-vipers, Gloydius shedaoensis Anima l Behaviour 63, 565-576 Thery, M & Casas, J (2002) Predator and prey v iews of spider camouflage Nature 10/1, p133 Weislo, W.T & Schatz, B (2003) Predator recogn ition and evasive behaviour by sweat bees, Lasioglossum umbripenne (Hymenoptera: Halictidae) in response to predation by ants, Ectatomma ruidum (Hymenoptera: Formicidae) Behaviour Ecology and Sociobiology 53, 182-189


3. ADVANTAGES AND DISADVANTAGES OF CACHING BEHAVIOUR Some animals eat their food as soon as they fi nd or capture it. Others will store (cache or hoard) it f or later. Caching occurs in some species of birds (eg: western scrubjays) and mammals (eg: squirrels). Thi s is particularly useful when food supplies are low or unpredictable at certain times of the year, like wi nter (table 3.1). There are factors that influence whether a foo d item is cached or eaten immediately (Dally et al 2006): � Perishability; � Handling time (ie: time taken to eat item); � Presence of other animals who eat same food (ie:

potential pilferers from same or different species) and risk of kleptoparasitism (food stealing);

� Observer identity - whether observer is attentive

(threat)(eg: social species like rooks) or inattent ive (not pilfering threat)(eg: asocial species like Cla rks nutcrackers);

� Position in social hierarchy; � Food value (ie: energy gained). ADVANTAGES 1. Means food available during winter. 2. Means food available during shortages or when un predictable. 3. Better for animals that active throughout the ye ar rather than those which build up fat stores and hibernate. 4. Not dependent on living near large food sources or waiting for binge periods (eg: migration). 5. Useful when too much food to carry home or eat a t one time. 6. Quicker to store food than consume it. This is i mportant when there is a high risk of predation, or living with f ood competitors as in groups. 7. Immediate consumption of food limited by amount of fat that animal can store or else food item wasted. 8. Animals can cache in one place (larder) or in mu ltiple sites (scatter caching).


9. Allows storage for when greater demand (eg: offs pring born). 10. Part of the evolution of sophisticated behaviou rs like planning. DISADVANTAGES 1. Problems of storing food, like degradation. 2. Risk of theft of cache (pilferage) from own or o ther species. 3. Risk of forgetting where cache hidden. Needs ani mal to have well developed memory to work if scatter caching used. 4. Risk of predation while retrieving cache. 5. Cache may be inaccessible when needed (eg: snow covers ground where food buried). 6. Requires the ability to plan. 7. Immediate consumption of food stops competitors from getting it. 8. Problems of defending larder. 9. Energy wasted with pilfering avoidance strategie s (eg: moving further away to cache or pretending to cache). 10. Not good strategy for food with low energy cont ent (ie: expend more energy caching and retrieving than gaining ene rgy), unless absolute food shortage. Table 3.1 - Advantages and disadvantages of caching food. FINDING THE CACHE Grey squirrels may have left food in over 10 0 00 different locations, which they recover with a combination of visual landmarks, scent marking and memory (Cline 2005). They are using scatter caching. There is evide nce of them refreshing their memory of cache sites by chec king them and moving around caches ("Life of Mammals: Chisellers" 2002; BBC Television). Kamil and Jones (1997) showed that Clarks nutcrackers (Nucifraga columbiana)(figure 3.1) use a "cognitive map" to find their cache. The experiment used a sandy room with two landmarks which were changed in position each time. The experimenters always buried the seeds half way between the two landmarks. The birds were allowed into the room four times per day for 50-60 days. Within fifteen days they could accurately find the seeds each time. They had learnt the geometrical relation ship between the buried seeds and the two landmarks, whi ch is the characteristic of a cognitive map.


(Source: US Fish and Wildlife Service)

Figure 3.1 - Clarks nutcracker. The hippocampus is the area of the brain linke d to memory, and particularly spatial memory. It can exp and in some species (eg: black-capped chickadees) in the a utumn when caching for the winter (Smulders et al 1995). While rats with damage to that area could not remember th e location of a platform in the Morris selection task (or open-field water maze procedure)(Jarrard 1995). The Morris selection task (Morris 1981, 1984) involves a pool of water with a hidden platform. Initially, the rats swim around until they hit the platform by chance and then climb on. Subsequently, when


put in the pool, they swim straight to the platform showing evidence of spatial memory. CACHING AND SOPHISTICATED BEHAVIOUR Caching is associated with sophisticated behav iour by the animals that use the strategy. Adaptability Squirrels cache nuts. In North America, they c an distinguish two types of oak nuts - those that germ inate soon which are eaten immediately, and those that germinate later which are cached. When there is a shortage of the latter, the squirrels collect oak n uts that germinate soon and remove the germinating part of the seed before caching ("Life of Mammals: Chiselle rs" 2002; BBC Television). Foresight and Planning Western American crows (Corvus brachyryhchus hesperis) were observed to eat bigger walnuts immed iately and bury smaller ones 1-2kms away. This meant high energy now and the loss of smaller nuts not such a problem (Cristol 2001). Western scrubjays (Aphelocoma californica)(fig ure 3.2) were found to recover perishable items first f rom their cache. This could be evidence of an internal representation of the future (Clayton et al 2001). These birds have shown planning in a recent experiment (Raby et al 2007). The scrubjays were pu t in special cages divided into sections in the evening and in the morning. In one section there were given food i n the morning ("breakfast room") and in another not ("no-breakfast room"). When given pine nuts in the eveni ng, the birds buried three times as many in the sand of the "no-breakfast room" as they did not know which sect ion they would be placed in the morning. Using the same cage set-up, the birds were giv en different foods (peanuts or dried dog food) in diff erent sections of the cage in the morning. When in the ca ge in the evening with food, they buried the opposite foo d to where given in the morning. So they buried dried do g food in the cage section where fed peanuts in the mornin g and vice versa.


(Source: US National Park Service)

Figure 3.2 - Western scrubjay. Crows also show evidence of planning. They cac he clams during low tide because not available during high tide ("Bird Brains" 1999; National Geographic Chann el). PILFERAGE RISK There is always a trade-off between the benefi ts of hoarding food and the cost of loss from pilferage. Cache pilfering has been seen in a number of s pecies who cache food (Dally et al 2006)(table 3.2). Stealing from other species (heterospecifics) � Grey jays (Perisoreus canadensis) and Stellar's jay s (Cyanocitta

stelleri) � Great tits (Parus major) from marsh tits (Poecile p alustris) � Eurasian jackdaws (Corvus monedula) from rooks (Cor vus frugilegus) Stealing from own species (conspecifics) � Grey squirrels (Sciurus carolinensis) � Pinyon jays (Gymnorhinus cyanocaphalus) � Mexican jays (Aphelocoma ultramarina) � Clarks nutcrackers (Nucifraga columbiana) � Western scrubjays (Aphelocoma californica) � Common ravens (Corvus corax) Table 3.2 - Animals known to do cache pilferage.


Cache pilfering may not be such a problem if t he pilferers are genetically related to the storer (in direct fitness)(Smulders 1998), or if the storers are also pilferers themselves and make up for own losses ("reciprocal pilferage")(Vander Wall and Jenkins 20 03). For example, North American red squirrels (Tamiasciurus hudsonicus) lost 25% of their stored cones, but pilfered 26% of those they ate (Gerhardt 2005). In terms of indirect fitness, it is the benefits to th e genes rather than to the individual. So theft of fo od by a brother, for example, makes evolutionary sense. When there is risk of pilfering, the cachers c an use cache protection behaviours (Dally et al 2006): i) Eat food immediately; ii) Cache more to offset predicted loss (eg: e astern chipmunks; Tamias striatus). But hard to predict lo ss and extra effort needed; iii) Cache in many different sites making it unprofitable for pilferers to find. But needs cache r to have good memory; iv) Cache less or not at all in presence of observers. v) Cached behind a large obstacle when observe rs present (eg: ravens; Bugnyar and Kotrschal 2002); vi) Delay caching until alone (ie: "out of vie w" of competitors); vii) Defend cache items ("larder-hoarders" kee p all cache in one place). But risks from fighting; viii) Cache in sites difficult to find for competitors (ie: "hard-to-see" sites); ix) Move caches after observers gone (recachin g); x) Misinformation - pretend to cache or appear not to have food item. If observers go, then cacher has waiting risks (eg: predation, loss of food), but a benefit when alone. Different strategies are needed if food competitors are constantly present (table 3.3).


CONSTANT PRESENCE COMPETITOR PRESENT BOTH OF FOOD COMPETITOR SOMETIMES ii; iii; vii; viii iv; v; vi; ix i; v; x (Numbers refer to cache protection strategies liste d above) Table 3.3 - Cache problem strategies depending on w hether food competitors are constantly observing or not. Animals that cache have been shown to adapt th eir behaviour in response to cache pilferage in differe nt ways (Dally et al 2006): � Change food type cached; � Change from scatter to larder hoarding; � Eating caches immediately. Western scrubjays also show evidence of the ab ility to imagine another individual's behaviour. Birds th at had stolen food from other caches were more careful in hiding their own cache from observers (Emery and Clayton 2 001). One way to combat cache pilferage is through "behavioural deception". This is "the use of false signals to modify the behaviour of a receiver in a way that benefits a sender, at some cost to the receive r" (Semple and McComb 1996). The use of behavioural deception has been seen in grey squirrels (figure 3.3). This includes covering additional empty cache sites ("deceptive caches") i f other squirrels were present (Steele et al 2008). Squirrels were observed at three different sit es in north-eastern USA. Deceptive caching was observed i n around 10% of caches, and was more likely when at l east three other squirrels were present and in close pro ximity (average of six metres away). Overall, pilferage avoidance behaviours were evident in around one-thi rd of cachings. Leaver et al (2007) observed the pilferage avo idance strategies of eastern grey squirrels at their unive rsity campus (University of Exeter, England). The number of caches made in the presence or absence of another squirrel was not significantly different (mean 3.2 vs 4.2), nor in the presence or absence of birds (eg: carrion crows, Corvus corone)(mean 3.3 vs 4.4). But the cachers were more likely to face away from other squirrels when burying food (52% of caches), yet no t when only birds present. Also caches were spaced further away (average three metres apart) because "travelling fu rther between successive caches may serve to distract the attention of an observer, which may descrease the


likelihood of that observer engaging in area-locali sed search" (p26).

(Source: MONGO)

Figure 3.3 - Grey squirrel. The strategies used by cachers and pilferers i s an example of an "evolutionary arms race" (Bugnyar and Kotraschal 2002). This is where the development of a strategy on one side leads to the development of competing strategy on the other. For example, the evolution of the ability to learn where cache sites from observing cachers is countered by caching "out of v iew". REFERENCES Bugnyar, T & Kotrschal, K (2002) Observational learning and the raiding of food caches in ravens, Corvux corax: Is it "tactical" deception? Animal Behaviour 64, 185-195 Clayton, N et al (2001) Elements of episodic-l ike


memory in animals Philosophical Transactions of the Royal Society B 356, 1483-1491 Cline, P (2005) Animal Cameo: Grey squirrel - Sciurus carolinenesis Feedback September, p5 Cristol, D (2001) American crows cache less preferred walnuts Animal Behaviour 62, 331-336 Dally, J.M et al (2006) The behaviour and evol ution of cache protection and pilferage Animal Behaviour 72, 13-23 Emery, N & Clayton, N (2001) Effects of experi ence and social context on prospective caching strategie s by scrubjays Nature 414, 443-446 Gerhardt, F (2005) Food pilfering in larder-ho arding red squirrels (Tamiasciurus hudsonicus) Journal of Mammalogy 86, 108-114 Jarrard, L.E (1995) What does the hippocampus really do? Behavioural Brain Research 71, 1-10 Kamil, A.C & Jones, J.E (1997) The seed-storin g corvid Clark's nutcracker learns geometric relation s among landmarks Nature 390, 276-279 Leaver, L et al (2007) Audience effects on foo d caching in grey squirrels (Sciurus carolinensis): Evidence for pilferage avoidance strategies Animal Cognition 10, 23-27 Morris, R.G.M (1981) Spatial localization does not require the presence of local cues Learning and Motivation 12, 239-261 Morris, R.G.M (1984) Developments of a water-m aze procedure for studying spatial learning in the rat Journal of Neuroscience Methods 11, 47-60 (pdf at http://pages.towson.edu/bdevan/Morris%20articles/Mo rris,%201984.pdf ) Raby, C.R et al (2007) Planning for the future by western scrubjays Nature 445, 919-925 Semple, S & McComb, K (1996) Behavioural decep tion Trends in Ecology and Evolution 11, 34-37 Smulders, T.V (1998) A game theoretical model of the evolution of food hoarding: Applications to the Par idae American Naturalist 151, 356-366 Smulders, T.V et al (1995) Seasonal variation in


hippocampal volume in a food-storing bird, the blac k-capped chickadee Journal of Neurobiology 27, 1, 15-25 Steele, M.A et al (2008) Cache protection stra tegies of a scatter-hoarding rodent: Do tree squirrels eng age in behavioural deception? Animal Behaviour 75, February, 705-714 Vander Wall, S.B & Jenkins, S.H (2003) Recipro cal pilferage and the evolution of food-hoarding behavi our Behavioural Ecology 14, 656-667


4. ADVANTAGES AND DISADVANTAGES OF TERRITORIALITY Some animals have a fixed territory (territori ality) while others are mobile. Territoriality is defined as "the defence of a fixed physical space with the pur pose of excluding individuals that are not members of th e social group" (Darden and Dabelsteen 2008 p905). Importantly, it is the area defended against indivi duals of the same species (Gese 2001). The territory may be defended permanently (all year round) or seasonally, and the defended area can inc lude nesting sites, food supplies, and/or sexual partner s. Territory is defended in different ways includ ing aggressive physical contact (direct defence) and si gnals of borders (eg: scent markings)(indirect defence). In some cases, animals may have more than one territory: for example, oystercatchers have two territories - inland where they nest, and on beach where they feed (Sparks 1969). Territoriality has a number of advantages and disadvantages (table 4.1). ADVANTAGES 1. Males able to hold on to resources show their ev olutionary fitness and are attractive to females. 2. Exclusive access to food, particularly at times of shortage. 3. Exclusive area for breeding and raising young. 4. Space for sexual display and courtship. 5. Spacing of animals avoids competition. 6. Reduces aggression. 7. Local knowledge of predators and resources. 8. Exclusive place to retreat and shelter. 9. Dispersion of nests reduces predation. 10. Higher survival rates. 11. Benefits in growth (eg: convict cichlids in lar ger territory grew quicker; Kim et al 2004). DISADVANTAGES 1. Cost of defending territory including risk of ph ysical contact, and displays of strength.


2. Need to be vigilant for intruders. 3. Defending territory is time that could be feedin g or mating. 4. Vocal or visual communication of territory owner ship makes the individual vulnerable to predation. 5. Difficult for smaller animals to hold territory; ie: more likely to be attacked than larger animals (eg: smaller Eur opean common toads received 240 attacks compared to 35 for larger toad s; Davies and Halliday 1979). 6. Difficult to move if resources exhausted. 7. Importance of territory size. If too large, then hard to maintain control. If too small, not enough resources for eff ort of defending. 8. Higher risk of predation if territory within pre dator's territory. 9. Easy for predators to find. 10. Ever present threat of take-over as surplus of animals without territory. 11. Extra vigilance required at certain times of th e year (eg: breeding season). Table 4.1 - Advantages and disadvantages of territoriality. There are three main reasons for territorialit y which varies between species (table 4.2). REASON FOR TERRITORY NUMBER OF SPECIES (from 40; Wilson 1975) 1. Control food supply 14 2. Retreat; shelter; nest 8 3. Access to females; space for sexual display; courtship 18 Table 4.2 - Main reasons for territories among diff erent species. Maher and Lott (2000) assessed the variables t hat influenced whether an animal is territorial or not (table 4.3). But how each of the variables influences territoriality can be unclear with contradictory re sults from studies. For example, twelve studies reported that territoriality declined as food quantity increased and four studies that increased food produced increased territoriality, while a few studies found no relati onship (Maher and Lott 2000). Only some of the studies wer e experiments.


FOOD NON-FOOD OTH ER CHARACTERISTICS RESOURCES - quantity - distribution - p opulation density - predictability - quantity - h abitat features - distribution - predictability - m ating - quality - quality - s pace - renewal rate - r efuges/spawning/ - type home sites - density - p redation pressure - accessibility - h ost nests (for b rood parasites) - e nergy availability Table 4.3 - Factors influencing whether an animal i s territorial or not. Maher and Lott felt that the relationship betw een many variables and territoriality is an inverted U- shape; eg: "very abundant food and very scarce food would not be defended, but intermediate levels would be defended " (p18). Not only individuals but groups also defend territory. Gese (2001) observed 112 instances of territory defence in Yellowstone National Park, Wyo ming, USA by coyote (Canis latrans)(figure 4.1) packs. A number of patterns were seen: � The main coyotes involved in territory defence were

alpha males (77% of chases observed) or alpha femal es (59%);

� The majority (three-quarters) of the intruders were

evicted without physical contact (ie: chasing was enough). Physical contact did not involve serious injury;

� The average chase was 2.87 minutes and up to 1km un til

the territory boundary; � Territory defence increased during the breeding sea son

(January-February), the gestation season (March), a nd when the pups emerged from the den (June);

� Territorial coyotes had advantages over transient

animals, but the nature of the advantages varied wi th position in the pack social hierarchy. Alpha coyote s had the greatest advantage in terms of breeding, wh ile beta animals rarely did and transients not at all. All territory members gained in feeding terms compared to transients - greater capture rate of small mammals (2.3 per hour vs 2.0) and greater capture success (alpha s 38.2% vs 32.3% for transients).


(Source: marya (emdot))

Figure 4.1 - Coyote. Usually residents are protective of their terr itory from outsiders. But Davis and Houston (1981) noted two unrelated pied wagtails (Motacilla alba)(figure 4.2)(owner and "satellite") defending winter feedin g territory together because they could achieve a one -third higher feeding rate than alone. Lone birds spotted 60% of intruders on their territory while two birds spotte d 85%. This is an example of mutualism where co-operation between two individuals benefits both more than competition between them (Hinde 1982). Territorial defence is costly. For example, Gi ll and Wolf (1975) estimated the cost of territory defence for individual golden-winged sunbirds (Nectarinia reich enowi) was three times more per unit of time of energy com pared to feeding for the equivalent time (1000 kCals fora ging vs 3000 kCals chasing intruders away). But these bi rds in East Africa that collect nectar from flowers in the ir territory saved 780 calories by having a territory rather


than mobile foraging.

(Source: sannse)

Figure 4.2 - Pied wagtail. COMMUNICATING TERRITORY OWNERSHIP AND DISPUTES One way to communicate territory ownership is through vocal signals, like barking. Darden and Dabelsteen (2008) investigated such behaviour among the male swift fox (Vulpes velox)(figure 4.3) observed in north-east Colorado, USA. The study included an aco ustic playback experiment (table 4.4) which involved play ing the call of a strange male fox to measure the respo nse of resident male foxes. The researchers found that resident males resp onded with barking to the recording of a strange male wit h greater intensity and much quicker when the playbac k occurred in the core area of the territory compared to the edge (average 226 seconds to respond for inner area vs 471 seconds for outer area).


(Source: en:user:cburnett)

Figure 4.3 - Swift fox. ADVANTAGES 1. Researchers can control and test exactly what in terested in studying. 2. Includes control group (eg: sound of neutral ani mal like a cow) to compare with the experimental group. 3. Able to establish cause and effect. 4. Standardised procedure and recordings. DISADVANTAGES 1. Problems of accurately recording calls. 2. Involves interference by the researchers into th e life of the animal. 3. Artificial - eg: no associated smell when using speaker, so resident may realise not real intruder. 4. Time-consuming to collect recordings and expensi ve in terms of equipment. Table 4.4 - Advantages and disadvantages of acousti c playback experiments. In the case of frogs, if another male approach es the territory, a "vocalisation battle" occurs. If the intruder does not withdraw, the two males will wres tle


until one is forced onto his back (Emlen 1968). Wel ls (1981) reported observing a fight of over two hours in Trinidad. Residents tend to do better in fights, an d win over 90% of contests (Stewart and Rand 1991). After disputes between neighbours are resolved , the residents only respond aggressively to strangers. T his is known as the "dear-enemy truce-relationship" (Jaege r 1981), and saves energy and reduces the risk of end less fights. ROBINS Generally the robin (Erithacus rubecula) is a solitary bird, and is strongly territorial (except during severe winters; Lack 1965). Migrant robins have bee n found to be territorial even during a stop-over in migration. Nelson (1907) observed territorial behav iour on a boat at sea where a group of robins had rested . Both sexes have their own individual territori es outside of the breeding season. There are two phase s to the territorial behaviour in the year. The individu al territory for most of the year, and the joining tog ether of two birds to breed. a) Individual territory The average size in English studies varies bet ween 0.27-0.73 hectares (approximately 450-2000m²) per b ird (Harper 1988). There is no evidence of sex differen ces in the size of the territory, nor it being related to food density. Sedentary (non-migratory) birds defend the sam e territory for their whole life, while migrants retu rn to the same sites each year. b) The breeding territory Two birds will join together during the breedi ng season, usually by the female moving to a male's territory (78% of cases observed). In 10% of observations, the male goes to the female's winteri ng territory, and 9% of times adjacent territories are fused together. Occasionally, the birds will pair together and then move to a new site: only 3% of 92 pairs studied in Cambridge did this (Harper 1988). The average size of the breeding territory is 0.55-1.44 hectares (approxima tely 900-2500m²) (Harper 1988). Unpaired males can be evicted from their terri tories at this time.


Aggression Peek (1972) noted three levels of defence in b irds: i) Vocal communication as a long-range warning; ii) Visual displays when visual contact made; iii) Chased and attacked if other levels failed to repel intruders. Because robins are strongly territorial, there is a high level of antagonistic encounters. Most occur w hen territories are being established or when there are boundary changes (at the beginning of the breeding season). Usually the display of the red breast is e nough. The back of male European robins is camouflage d, but the puffed-up red chest is a warning signal to othe r males. Lack (1943) has found the red breast is a "s ign stimulus" 1 for territorial aggression against intruders. Robins will attack just red feathers, such is the strength of the stimulus. The resident bird flies a t the intruder with a high-pitched call. If the intruder does not leave, the resident then perches on a branch an d displays its red breast. Occasionally this "show of strength" does not work, and a fight ensues. But 13% of 1067 encounters observed end in fig hts (Harper 1988). These fights can be fatal: in a Camb ridge study, 10% of 98 males and 3% of 86 females died in this way (Harper 1988). Once the territories have been established, th e residents are able to distinguish the calls of thei r neighbours from strangers occupying territories fur ther away. In this situation, the direct neighbour is no t seen as a threat. This is known as the "dear enemy pheno menon" (Wilson 1975). Recognition of the neighbour avoids wasteful conflicts, and makes clear the boundary ed ges of the territory. There are a number of possible explanations fo r the "dear enemy phenomenon": � Habituation to the neighbour's song - each time it is

heard, it produces less of a territorial aggression response until there is no response at all to the s ong;

� Mere exposure effect - similar to above; � Dialect convergence - the similarity in the neighbo urs'

1 "Sign stimulus" is a trigger for instinctive behaviour (Hinde 1982). For example, the red of the breast triggers the territorial aggression response. The trigger must have certain specific characteristics. Lack (1943) found no territorial aggression response to models of robins without the red breast.


songs reduces the territorial aggression response. The "dear enemy phenomenon" is dependent on th e resident recognising their neighbours' calls from strangers' calls. Hardouin et al (2001) found that male little owls (Athene noctua)(figure 4.4) did not res pond to neighbours' hoots played back from the usual loc ation, but only if played from an unusual location. Based in west France, this study used the "four-stimuli play back discrimination paradigm". This involves recordings of two sets of calls (neighbour and stranger) played from two different places (usual and unusual locations).

(Source: Artur Mikolajewski)


Figure 4.4 - Little owls. Where the playback came from the usual locatio n of neighbours, there was a clear difference in respons e by residents towards neighbours and strangers. Strange r calls elicited more hoots per minute (13 vs 9 for neighbours), and for longer duration (average 200 s econds vs 125 seconds). But when the playback came from an unusual location, there was no difference in respon se by residents towards neighbours and strangers. Residents learn to discriminate familiar calls of neighbours when they originate from the expected direction. The two characteristics of sound and dir ection is what the resident becomes habituated towards (Be e and Gerhardt 2001). Residents Always Win Research has found that residents in a territo ry tend to defeat the challengers in most cases. Mayna rd Smith and Parker (1976) suggest possible explanatio ns: i) Value asymmetries - greater investment and local knowledge about predators and resources gives the resident advantages to win the contest; ii) Resource-holding power (RHP) variations - those in residence have superior abilities (eg size) that allows them to defeat intruders; iii) "Owners always win" convention - the indi vidual in possession of the territory fights harder than t he intruder. This is an example of a "bourgeois strategy"; ie: a strategy that cannot be bettered in a population. T his idea is the part of the application of game theory to animal behaviour (Maynard Smith 1982). Tobias (1997) tested the first explanation wit h a series of "removal-replacement experiments" with 75 robins. This involves removing the residents from t heir territories for a period of time, and then returnin g them, to see if they can win the territory back fro m the "new residents". Tobias removed 37 males and 13 fem ales from their winter territories, and 19 males and six females from the spring territories. The length of the removal varied from 1-14 days. Two observations came from the research: � For winter territories, the longer the resident was

away the less likely they were to win back the territory. Less than five days away, all won back t heir territory, but if away for more than 10 days, no


returnees won; � With the spring territories, there was an immediate

loss no matter how short the period away. This is because territory is crucial for males at this time of the year. Males without territory have little chanc e of breeding.

REFERENCES Bee, M.A & Gerhardt, H.C (2001) Neighbour-stra nger discrimination by territorial male bullfrogs, Rana catesbeiana: II. Perceptual basis Animal Behaviour 62, 1141-1150 Darden, S.K & Dabelsteen, T (2008) Acoustic territorial signalling in a small, socially monogam ous canid Animal Behaviour 75, 905-912 Davies, N.B & Halliday, T.R (1979) Competitive mate searching in male common toads, Bufo bufo Animal Behaviour 27, 1253-1267 Davies, N.B & Houston, A.I (1981) Owners and satellites: The economics of territory defence in t he pied wagtail, Motacilla alba Journal of Animal Ecol ogy 50, 1, 157-180 Emlen, S.T (1968) Territoriality in the bullfr og, Rana catesbeiana Copeia 2, 240-243 Gese, E.M (2001) Territorial defence by coyote s (Canis latrans) in Yellowstone National Park, Wyomi ng: Who, how, where, when and why Canadian Journal of Z oology 79, 980-987 Gill, F.B & Wolf, L.L (1975) Economics of feed ing territoriality in the golden-winged sunbird Ecology 56, 2, 33-45 Hardouin, L.A et al (2001) Neighbour-stranger discrimination in the little owl, Athene noctua Ani mal Behaviour 72, 105-112 Harper, D (1988) Erithacus rubecula Robin: Soc ial pattern and behaviour. In Cramp, S (ed) Handbook of the Birds of Europe, the Middle East and North Africa V ol V Oxford: Oxford University Press Hinde, R (1982) Ethology London: Fontana Jaeger, R (1981) Dear enemy recognition and th e costs of aggression between salamanders American Naturalist 117, 962-974


Kim, J.W et al (2004) Interactions between pat ch size and predation risk affect competitive aggressi on and size variation in juvenile convict cichlids Animal Behaviour 68, 1181-1187 Lack, D (1943) The Life of the Robin London: H.F & G Witherby Lack, D (1965) The Life of the Robin London: Penguin Maher, C.R & Lott, D.F (2000) A review of ecol ogical determinants of territoriality within vertebrate sp ecies American Midland Naturalist 143, 1-29 Maynard Smith, J (1982) Evolution and the Theo ry of Games Cambridge: Cambridge University Press Maynard Smith, J & Parker, G (1976) The logic of asymmetric contests Animal Behaviour 24, 159-175 Nelson, T (1907) The Birds of Yorkshire London: A Brown & Sons Peek, F.W (1972) An experimental study of the territorial function of vocal and visual displays i n the male red-winged blackbird (Agelaius phoeniceus) Ani mal Behaviour 20, 112-118 Sparks, J (1969) Bird Behaviour Harmondsworth: Penguin Stewart, M & Rand, A (1991) Vocalisations and the defence of retreat sites by male and female frogs, Eleutherodactylus coqui Copeia 1991, 1013-1024 Tobias, J (1997) Asymmetric territorial contes ts in the European robin: The role of settlement costs An imal Behaviour 54, 9-21 Wells, K (1981) Territorial behaviour of the f rog, Eleutherodactylus urichi in Trinidad Copeia 1981, 726-728 Wilson, E (1975) Sociobiology Cambridge, MA: Belknap Press


5. ADVANTAGES AND DISADVANTAGES OF DELAYED BREEDING IN BIRDS From an evolutionary viewpoint, it makes sense to have as many offspring as possible over a bird's lifetime. Yet there are some birds that have delaye d breeding. This means that breeding does not take pl ace as soon as the bird is physically able. For example, t he albatross first breeds at between 7-13yrs old. There are a number of reasons for delayed bree ding (Gill 1995): i) The life expectancy of the bird. Birds that live longer have greater opportunit ies for breeding over the lifetime, so can afford to wa it. For example the Wandering Albatross (Diomedea exulans)(figure 5.1) produces one chick every two y ears for up to 50 years (Gill 1995).

(Source: Mila Zimkova)

Figure 5.1 - Wandering albatross. ii) The interval between generations (mean generation time). Successful breeding is not just about having m any offspring, but about them surviving into adulthood.


Spacing out the offspring allows more time to be sp ent on their upbringing, and thus increases their survival . iii) Costs of early reproduction can be severe . Birds that breed young may be more likely to d ie from lack of food or poor predator avoidance, and t hus so will the offspring die. Older birds may be better a t collecting food for the incubation/pregnancy period , and finding nests that avoid predators. Ainley and DeMaster (1980) studied the risk of breeding among Adelie Penguins (Pygoscelis adeliae) , who show delayed breeding patterns. In one year, 39% of breeding animals died compared to only 22% of non-breeders. While 75% of 3-year-old females died at f irst breeding compared to only 10% of 11-year-olds at fi rst breeding. There are survival advantages to delayed breeding. iv) Divorce more common among younger individu als of monogamous species (eg: short-tailed Shearwater; Wo oller and Bradley 1996). Table 5.1 compares delayed breeding to immedia te breeding in two birds. ALBATROSS DUCK Type of breeding delayed immedia te Survival before breeding (per year)(%) 30 15 First reproduction (age in years) 7-13 1 Fecundity (young per year) 0.2 3 Adult mortality (per year) (%) 5 50 (After Gill 1995) Table 5.1 - Comparison of delayed and immediate bre eders. Table 5.2 lists the general advantages and disadvantages of delayed breeding for birds. ADVANTAGES


1. Older birds can learn about raising offspring fr om time helping relatives raise offspring. 2. Older birds better skilled at collecting food, w hich important when offspring born. 3. Less older birds die at first breeding. 4. Suitable for long-living birds that can produce offspring for many years. DISADVANTAGES 1. Bird could die before breeding and thus no offsp ring. 2. Not suitable for short-living birds. 3. Goes against basic principle of evolution which is to have as many offspring as possible. 4. What does the bird do while waiting for age to b reed? Table 5.2 - Advantages and disadvantages of delayed breeding. REFERENCES Ainley, D.G & DeMaster, D.P (1980) Survival an d mortality in a population of Adelie Penguins Ecolog y 61, 522-530 Gill, F.B (1995) Ornithology (2nd ed) New York: WH Freeman Woller, R & Bradley, S (1996) Monogamy in long-lived seabird: The short-tailed Shearwater. In Blac k, J.M (ed) Partnerships in Birds Oxford: Oxford University Press

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