The social behaviour of free-ranging suburban dogs

Applied Animal Ethology, 10 (1983) 5-17 5 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

THE SOCIAL BEHAVIOUR OF FREERANGING SUBIJRSAN DOGS

MICHAEL BERMAN’ and IAN DUNBAR

Department of Psychology, University of California, Berkeley, CA 94720 (U.S.A.)

(Accepted for publication 5 August 1982)

ABSTRACT

Berman, M. and Dunbar, I., 1983. The social behaviour of free-ranging suburban dogs. Appl. Anim. Ethel., 10: 5-17.

Over a period of 7 months, a residential area of Berkeley, California, was surveyed at hourly intervals throughout the day and night for free-ranging dogs, dogs with people, and cats. The animals’ locations and behaviours were recorded. The highest frequency of sightings of free-ranging dogs occurred at 07.00 h, with a secondary peak at 17.00 h. The abundance of dogs with people followed a similar pattern except that the morning peak occurred 2 h later. Cats were most abundant at night between 18.00 and 04.00 h. The observable number of free-ranging dogs increased with increasing temperature to a maximum at 23” C and then declined with higher temperatures. The number of cat sightings was fairly constant with increasing temperature up to 17°C and then declined with further temperature increase. Free-ranging dogs were sighted most frequently on private property. Street and sidewalk use was greatest in the mornings; free-ranging dogs tended to travel in the morning and rest as the temperature increased later in the day. Most dogs were sighted within 1 or 2 blocks of their homes. The home ranges of 8 dogs are illustrated and described. These showed considerable individual variation, but generally had dense core areas and sparse travel areas (mean corridor home range = 1.74 hectares). Most free-ranging dogs were solitary and social groupings occurred only randomly. Despite their apparent lack of sociability, the dogs did not exhibit any signs of territoriality and agonistic encounters were never observed.

INTRODUCTION

The growing awareness of problems caused by free-ranging domestic dogs in urban and rural areas is evident from the increasing number of articles on this topic in popular and scientific journals. Rural free-ranging dogs have been discussed fairly extensively because of reports that they prey heavily on wildlife and domestic livestock ( Perry and Giles, 1970; Gipson, 1972; Scott and Causey, 1973; Nesbitt, 1975). However, there have been fewer reports on urban free-ranging dogs, and these have mainly emphasised public health and environmental problems (Berzon et al., 1972; Feldman and Carding, 1973; Beck, 1975; Loew and Fraser, 1977).

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Despite the considerable nuisance of free-ranging dogs in some urban areas, there have been very few studies investigating their general behaviour. Beck (1973) outlined the basic behavioural ecology of free-ranging dogs in several areas of Baltimore, Maryland; Fox et al. (1975) described a study of three feral dogs living in an area of St. Louis, Missouri; and more recently, Daniels (1980) investigated the social behaviour of free-ranging dogs in Newark, New Jersey. The above-mentioned studies have primarily concerned the behaviour of free-ranging animals in economically depressed urban neighbourhoods. The major objective of the present study was to document the abumlance, move- ment and association patterns of free-ranging domestic dogs in a “typical” suburban neighbourhood, in order to make an estimation of their social nuisance.

METHODS

The study was conducted in a 4%hectare, middle-class section of Berkeley, California (37.52 N, 122.17 W; population 107 400). After a city-wide survey, the residential site was chosen because of its good visibility, grid street pattern, abundance of free-ranging dogs and distance from business and shopping districts. The study area was bordered by 4 heavily trafficked streets and traversed either completely or partially by 10 residential streets that were kept free of most non-residential traffic by 5 well-placed traffic diverters. Except for a few small businesses, the area was entirely residential, containing both single and multiple housing units. Most houses had unfenced front yards and fenced back yards. The open space in the area consisted mainly of the unfenced front yards and a semi-developed park running along the north side of Hearst Avenue.

Test procedure

Observations were recorded on tape while driving a fixed route through the study area at approximately 15 m.p.h. with as little stopping as possible. Ob- servation sessions were started on the hour and lasted approximately 50 min. Between April and October 1977, the route was driven 105 times at different times throughout the day. The area was surveyed approximately 6 times for each hour between 06.00 and 24.00 h. The temperature was recorded at the beginning of each observation session at the intersection of Hearst Avenue and Grove Street.

Instantaneous samples (Altmann, 1974) were recorded for all free-ranging dogs, dogs with people, and cats that were sighted. A free-ranging dog was defined as “ . ..any dog observed without human supervision on public property or on private property with immediate unrestrained access to public property” (Beck, 1973). Dogs with people included any dog on public or private property, while under direct or indirect human control. This included dogs on a leash or tether and unrestrained dogs under supervision, i.e. dogs walking within 5 m of their owners.

The first time a dog was sighted in each session, its identity (if known), location, behaviour and companions were recorded. If an animal was seen more than once in an observation session, the additional sightings were used to determine home-range sizes but were not used in computing sample totals.

Initially, 10 simple categories were used to describe the behaviour of free- ranging dogs: rest (sitting or reclining); trauel (locomoting); investigation (sniffing an inanimate object); urinary marking (assuming a urinary posture as described by Sprague and Anisko, 1973, or Beach, 1974); defecation (assuming a defecation posture as described by Beach, 1974) ; greeting (sniffing and licking a conspecific); foraging (eating food that was not intended for dogs); agonistic (aggression directed towards a conspecific); sex (male and female mounting and thrusting, or locking as described by Beach and LeBoeuf, 1967); and play (social play including 2 or more dogs). Because of the small sample sizes in some categories, the 10 categories were collapsed into 5 for data analysis: urinary marking, defecating and foraging were combined and termed biological functions; greeting, play and sex were termed socio-sexual behaviour; agonistic behaviour was dropped because aggressive encounters were never observed; and resting, travelling and investigating were retained.

The location of each sighting was recorded to determine the distribution of free-ranging dogs relative to land use. Four land-use categories were designated; private property (the unfenced area on either side of the sidewalk); sidewalk (the paved area, including driveways, between the street and private property); street (the area between curbs) ; and park (developed or undeveloped open space).

Analysis

The relationship between time and the number of animals sighted during each observation period was determined for free-ranging dogs, dogs with people, and cats by calculating the mean number of animals observed at each hour of the day. The relationship between temperature and the abundance of free- ranging dogs and cats was determined by calculating the mean number of animals observed at each of eight 3” C temperature intervals between 7 and 30” C. Behaviour was analysed for differences related to time, temperature and land- use by analysis of variance.

Social groups were defined as 2 or more free-ranging dogs within 10 m of each other, either standing stationary or moving in the same direction while moni- toring each other’s behaviour. The recorded frequencies of different group sizes were compared with an estimated zero truncated Poisson distribution (Cohen, 1960) of expected group-size frequencies using a x2 test for goodness- of-fit (Snedecor and Cochran, 1967).

Land-use was analysed using an analysis of variance for differences related to time, temperature and behaviour. Spearman rank correlation coefficients were calculated for: (1) street use by free-ranging dogs and dogs with people;

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(2) traffic flow and street use by free-ranging dogs; and (3) traffic flow and street use by dogs with people.

Home range, the area in which the animal carries out its normal daily activities (Burt, 1943; Jewell, 1966) is an elusive measure that changes with the number of captures and/or sightings (Ables, 1969) and the methods of calcula- tion (Mech, 1966). Two methods were used to calculate minimum home range (Flowerdew, 1976): (1) the total home range was calculated by connecting the outlying sightings of an individual and determining the enclosed area without regard for site geography; and (2) the useable (corridor) home range was calculated by connecting the outlying sightings and determining the area to which the dog had access (unfenced private property, streets, sidewalks and parks).

RESULTS

Approximately 50 individuals were identified during the first 2 months of the study. Most identifiable individuals were seen less than 5 times; 5 were seen often enough (more than 10 times) and were distinct enough to allow positive identification during both day and night observations.

The total number of dog sightings was 1243. The majority of sightings (73.7%; 916) were free-ranging animals (mean abundance of 10.02 per hour); only 26.3% (327) of dogs were observed with people. The frequency of sightings at different times of the day and night for free-ranging dogs and dogs with people is illustrated in Fig. 1. The frequency of sightings of free-ranging dogs

1 FREE-RANGING DOGS

0600 12ca 1800 2400

Fig. 1. Mean number of sightings of free-ranging dogs and dogs with people at hourly intervals throughout the day and night.

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showed a marked diurnal variation. Free-ranging dogs were most abundant during the early morning and late afternoon. The highest frequency of sightings occurred at 07.00 h and gradually declined throughout the day until the mid-afternoon, whereafter abundance increased to reach a secondary peak at 17.00 h. The number of sightings then declined steadily to a nadir in the early morning (04.00-05.00 h). The abundance of dogs with people followed a similar pattern, with peaks in the early morning and late afternoon. The morning peak occurred at 09.00 h, 2 h after the morning peak for free-ranging dogs. The afternoon peak coincided with the afternoon peak for free-ranging dogs at 17.00 h.

The total number of cat sightings was 580, with a mean abundance of 6.26 per hour. Cats were most abundant at night, with the majority of sightings occurring between 18.00 and 04.00 h.

Throughout the period of the study, the temperature ranged from 9 to 29°C (mean 16.9”C). The observable number of free-ranging dogs increased with increasing temperature to a maximum of 10.7 sightings per hour per 3” C temperature interval at 22-24” C, and then declined with higher temperatures. In comparison, the number of cats sighted was fairly constant (mean 7.6 sightings per hour per 3“ C temperature interval) with increasing temperature until 16-18” C, and then steadily declined with further temperature increase to a low of 3 sightings per hour at 28-30” C.

Free-ranging dogs spent most of their time either resting or travelling (80.7% of sightings). The animals were observed resting in 44.4% (344) of the sightings, and in 36.3% (281) of instances the dogs were sighted travelling. Of the other sightings: 8.9% (69) of the dogs were investigating; 5.6% (43) were engaged in sociosexual behaviours; and 4.7% (37) were engaged in specific biological activities.

Resting and travelling were the only behaviours that varied significantly with either time and/or temperature. Free-ranging dogs tended to travel in the early morning and rest as the temperature increased later in the day. The mean number of dogs sighted resting increased significantly (F = 3.39, df = 88; P < 0.003) with increasing temperature for a low of 9.1% of dogs sighted at 7-9°C to a high of 63.6% of dogs sighted at 24-26” C. The mean number of dogs travelling was inversely related to the number of dogs resting, but did not vary significantly with temperature. The mean number of dogs travelling did, however, vary significantly with time (F = 12.12, df = 79; P < 0.001). The number of dogs travelling was greatest between 06.00 and 12.00 h (mean 4.7 dogs sighted per hour) and decreased steadily in the afternoon (12.00-18.00 h, mean 3.0 dogs per hour) and evening (18.00-24.00 h, mean 2.4 dogs per hour).

Most free-ranging dogs were solitary (82.2%; 742) or paired (14.2%; 128). A few dogs were sighted in groups of 3 (2.7%; 24) or 4 (0.9%;8); i.e. 742 dogs were sighted individually, groupings of 2 dogs were sighted 64 times, groups of 3 were observed 8 times, and groups of 4 were only seen twice. Larger groups were never observed within the study area, although groups of up to 7 animals have been observed by the authors within the Berkeley city limits.

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A zero truncated Poisson distribution was estimated following the techniques described by Cohen (1960), and compared with the distribution of social groupings. The differences between the distributions were not significant (X2 = 2.936, df = 4; P < 0.6), meaning that the social groupings most probably occurred randomly. Behavioural observations indicated that the groups were spontaneous, shifting and of short duration. Groups generally formed when solitary dogs met while travelling. After greeting, the individuals would either stay together for a short while, or move off in separate directions. Larger groups formed around a limited resource, such as food or shade, that attracted a changing population of dogs.

Only one pair of dogs, Spaniel and Terrier, appeared to maintain a stable social unit. These dogs lived across the street from each other and were left unrestrained during daylight hours. From April until June 1977, when Span- iel’s owners moved out of the study area, Terrier had been observed paired with Spaniel on 10 of 14 sightings (71.4%) and Spaniel had been observed with Terrier on 10 of 16 sightings (62.5%). During this time, Terrier was sighted alone twice, with another dog once, and once in a group of 3 that included Spaniel; Spaniel was sighted once in the same triad, once with other dogs and alone on 4 occasions. After Spaniel moved from the study area, Terrier was only observed with another dog once during 29 additional sightings between June and November 1977.

Free-ranging dogs were sighted most frequently on private property (58.9%; 455). Of the remaining sightings, 23.7% (183) of dogs were observed on the sidewalk, 15.4% (119) in the street, and 2.1% (16) in parks. Street and sidewalk use was greatest in the mornings between 06.00 and 12.00 h (F = 17.39, df = 79; P < 0.01) when travelling occurred with the greatest frequency. Other land use did not vary significantly with time or temperature. As expected, travelling free-ranging dogs were most frequently sighted when on public property (70.5%). Socio-sexual behaviours were observed with near equal frequencies on both public (51.2%) and private (48.8%) property. All other behaviours were observed predominantly on private property: resting (79.3%); biological activities (78.4%); and investigation (71.1%).

Free-ranging dogs and dogs with people used the streets of the study area with near equal frequency (p = +0.62; P < 0.05). There was no correlation between ranked street traffic and ranked street use by either group; i.e. neither group tended to avoid the busier streets that bordered the study area.

The total home range size was computed as a standard of comparison with other home-range studies. However, this was not an accurate measure of the area available for use by free-ranging dogs. The actual area available to the dogs was much smaller, and is represented by the corridor home range. This measurement only includes areas to which the dogs had direct access, such as streets, sidewalks, parks and front yards; it leaves out areas that are fenced and/or covered with buildings. (Of course, in some areas, buildings may have the opposite effect of adding to available space, if free-ranging dogs have access to more than one floor of the building; Reck, 1973.)

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Home ranges of Berkeley dogs showed considerable individual variation, but generally had dense core areas and sparse travel areas. The home ranges of 8 individuals are illustrated in Fig. 2. Total home range size varied from 0.01 to 8.43 hectares, with a mean of 3.49 hectares. Corridor home range size varied from 0.01 to 4.18 hectares, with a mean of 1.74 hectares.

Two individuals, Beagle (old female) and Mongrel (old female), had extreme- ly small home ranges of 0.01 and 0.02 hectares, respectively, that did not include any travel area. Beagle was sighted 12 times but was never sighted away from her porch. Mongrel was seen 27 times and was only observed away from her porch on 4 occasions.

Terrier (c. 2-year-old male) had 2 core areas, the smaller one at his owner’s house and a larger one at a neighbouring house across the street. Terrier’s fre- quent companion, Spaniel (young male), showed a similar pattern except that he was taken inside at night. Both Terrier and Spaniel had small home ranges of 1.32 and 1.25 hectares (total home ranges = 2.60 and 1.48 hectares, respectively).

Collie (old male) had a fairly large corridor home range of 2.4 hectares (total home range = 5.41 hectares). He was sighted on 42 occasions but was only seen away from his home 5 times. Four of these sightings were during his early-morning stroll, which occurred each morning after he was let out at 07.00 h (personal communication with owner). Collie’s range extended several blocks east of his home along Francisco Street but did not appear to extend west across Sacramento Street, a major thoroughfare only half a block west of his home.

Afghan’s (male) core area was larger and less well-defined than those of the above dogs and the location of his home was unclear. He was sighted most often at the intersection of Grant and Francisco (17 times), and was observed away from this area on 7 occasions. His corridor home range was 2.50 hectares and the total home range was 7.90 hectares.

The sightings of both Samoyeds were widely dispersed; Little Samoyed (female) and Big Samoyed (male) both lacked an obvious core area and had large home ranges of 2.65 and 4.18 hectares (total home ranges = 2.97 and 8.43 hectares, respectively). Because their ranging patterns were so different from the other individuals, it seems likely that the study area only contained a portion of their home ranges and maybe did not contain their homes. Al- though the sampling method was biased towards identifying dogs with small home ranges, the dispersed sightings of both Samoyeds indicate that some dogs might have very large home ranges.

DISCUSSION

The present study provides an account of free-ranging dog behaviour within a suburban area of Berkeley, California. When compared with other studies of economically depressed urban neighbourhoods, these results indicate that the behaviour of free-ranging dogs is not necessarily the same in all urban en-

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_~ ~~_._._ MONGREL 0.02 (27) BEAGLE 0.01 (12)

SACRAMENIO

L- EO‘A

i

I

a-

i NIA

L l-

-. TERRIER 1.32 (44) SPANIEL 1.25

GROVE

11 CALIFORNIA :r--qr

: r-- L 1 c

13

2.04 (42)

LITTLE SAMOYED 2.62 (lo)

AFGHAN 2.50 (25) J ,,,,,- u u I-hz L

BIG SAMOYED 4.16 (16) 3 u /L-J L_iL-_h_z_l L

SICRAMENTO

1

Fig. 2. Location of sightings of 8 dogs within the study area. Each map is identified by the designated name for each individual plus its corridor home range, with the number of sightings in parentheses.

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vironments and that associated problems may vary from one area to the next. The behaviour of free-ranging animals in the Baltimore study was strongly

influenced by the garbage-strewn alleys, which acted as a focal point for local dogs. The alleys gave the dogs a relatively secluded place to gather, and the garbage provided a source of food. Beck (1973) reported that 40.1% of dogs were sighted in alleys, 31.5% in the streets and sidewalks, 10.5% in empty lots and the remainder on porches or in parks and other areas, i.e. that in excess of 80% of dogs were sighted on public property. In the Berkeley study, there were no alleys and the dogs did not normally have access to garbage (unless they found their way into back yards) because the garbage was collected direct. ly from the backyard of each house and garbage cans were not placed in the street the night before collection. As a result, only 41.2% of dogs were sighted on public property and large congregations of dogs were not observed.

From his 14 morning samples, Beck (1973) reported that the majority of dogs sighted were travelling (68.0%) and that this behaviour occurred most frequently in alleys (37.7%) and to a lesser extent in streets (21.8%) and on sidewalks (14.8%). Only 19.2% of the dogs were observed resting. In the present study, most free-ranging dogs were sighted while resting on private property (44.4%), and only 36.3% of dogs were observed travelling on public property .

In addition to variations in behaviour that are related to topographical differences between study sites, it is apparent that cultural differences between neighbourhoods may exert an effect on the behaviour of free-ranging animals. The diurnal variation in abundance offers a fine example of how owners’ habits may affect the behaviour of their pets. Free-ranging dogs were most abundant in the early morning, around the time when people wake up and let their dog out for a morning run (personal communication with several owners). In comparison, dogs with people were most abundant 2 h later. This suggests that whereas some people are willing to perform minimum dog-care activities (such as opening the door to let their dog run outside) at a bright and early hour, before Animal Control personnel start their patrol, more responsible owners, who are not prepared to let their dogs run free, do not walk their pets until later in the morning. Similarly, the 1 h difference in peak abundance of free- ranging dogs between the Baltimore and Berkeley studies was probably related to differences in the time that people rise in the morning; the study areas in Baltimore were working-class districts where, presumably, people get up ear- lier than the residents (many of them students) of the Berkeley study site.

The multiple-sighting method used to determine home ranges yielded results (total home range) that were similar to the home ranges reported in previous studies. Using direct observation, Beck (1973) determined the home ranges of 2 feral dogs, one of which later became a pet. As feral dogs, they had a home range of 2.59 hectares. After becoming a free-ranging pet, the home range of one of the dogs became reduced to 0.52 hectares. The average home range in the New Jersey study was 0.79 hectares, and owned dogs had smaller home ranges than unowned animals (Daniels, 1980). Similar methods were used to

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determine the 61-hectare home range of the St. Louis feral pack described by Fox et al. (1975).

Unlike feral dogs, free-ranging domestic pets do not need to forage or hunt for their food. They are not governed by the same “bio-energetic” rules that govern wild animals (McNab, 1963). Instead, their movements are regulated by curiosity, habit and boredom rather than by hunger. In the present study, individual home range sizes were quite small, much smaller than those required to support feral animals of similar weight (McNab, 1963). Most free-ranging dogs were only occasionally sighted more than one block from their home.

The variability in the home range sizes was probably related to each dog’s individual “personality”, depending on its age, sex (and reproductive status), breed and health. With a larger sample size, it might be possible to classify the dogs as wanderers or non-wanderers according to these and other attributes. For example, it has been demonstrated that the tendency to roam may be decreased in 90% of dogs following castration (Hopkins et al., 1976). This find- ing is especially important since the majority of free-ranging dogs are males (Westbrook and Allen, 1979; Daniels, 1980).

The free-ranging dogs in the Berkeley study were usually solitary and spent the majority of their time resting on private property, or to a lesser extent travelling on public property. Observed instances of socio-sexual behaviours were quite rare (4.7% of sightings), and groupings that did form were aggregates of dogs rather than packs. Packs are social units that hunt, rear young and protect a communual territory as a stable group (Mech, 1966). Such activities were not observed in the temporary aggregates of free-ranging dogs sighted in the Berkeley study.

It is interesting to question why a social animal like the domestic dog does not behave in a social manner when it is allowed to roam freely. This dilemma has previously been considered by Daniels (1980). The characteristic advan- tages of group living that function in the wild (group hunting and feeding and the defence of territory) are not necessary in urban areas, where most pets are fed regularly or otherwise forage for food that is in plentiful supply. On the other hand, there are significant disadvantages in forming groups in a domestic setting. Groups of roaming dogs are not normally tolerated by the public. For instance, in the New Jersey study, 50% of all complaints to the Bu- reau of Dog Control in Newark concerned groups of 2 or more dogs, even though these dogs represented less than a quarter of the total free-ranging population (Daniels, 1980).

Despite their apparent lack of sociability, the dogs observed in the present study did not exhibit any signs of territoriality. The dogs appeared to roam freely throughout the home ranges of other individuals and agonistic encounters were never observed. For the most part, dogs appeared to be disinterested in the affairs of others. The lack of territoriality of free-ranging domestic dogs has been reported previously (Scott and Fuller, 1965; Beck, 1973; Bekoff, 1979; Dunbar and Carmichael, 1981).

In the Berkeley study site, the free-ranging dog problem appeared to be un-

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der reasonable control when compared with other more densely populated urban areas that have been studied. Most probably, the primary reason for this is that the majority of free-ranging animals were owned dogs that were only allowed to roam free for limited periods. When outside, most of these dogs spent the greater part of their time close to their homes. There was no evidence that dogs roamed in large packs. In fact, the dogs had small home ranges and were rarely seen in groups. On the whole, the dogs were reasonably well-behaved and were not seen to exhibit any signs of aggressive behaviour. In other studies, a high proportion of the free-ranging dogs were feral and thus exhibited a greater tendency to roam on public property.

Although the dogs in the Berkeley study caused little apparent disturbance, three-quarters of the dogs sighted were free-ranging and not under the direct or indirect control of their owners (even though leash laws were supposedly in effect). Although the dogs spent most of their time resting on private property out of harm’s way, they did have free access to public property and were frequently seen travelling the streets and sidewalks. Largely in view of their sheer abundance, free-ranging dogs pose some problems in this area: (1) although aggressive animals were never observed, some residents expressed se- vere concern and were admittedly afraid of some of the larger animals; (2) since the dogs do not avoid busy streets, they also constitute a not inconsid- erable potential traffic menace; and, in addition, (3) they deposit large quan- tities of urine and faeces, which apart from being a substantial aesthetic in- convenience, also represents an environmental (Nowell, 1978) and public health hazard (Hull, 1963; Bisseru, 1967; Beck, 1973). Of course, it may be argued that leashed dogs also contribute to the faeces problem, but when the dog is leashed the owner may at least impose some control over the discrete place- ment of faecal deposits.

The size of the free-ranging dog problem in the Berkeley area is best re- flected by statistics from the City of Berkeley Animal Care Services. Within an equivalent period (April-October) of the previous year, the Animal Care Service impounded and/or quarantined 910 dogs. Of these, only 29% (264) were redeemed and 18% were adopted. The majority of dogs (56%, 508) had to be destroyed.

ACKNOWLEDGEMENTS

This study was partially supported by USPHS Grant 04000 to Dr. Frank Beach from the National Institute of Mental Health. The authors would like to thank Dr. Frank Beach, Dr. Thelma Rowell, Dr. Alan Kamil and Dr. Bill Meredith for their advice and assistance in this study.

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Documents

The social behaviour of free-ranging suburban dogs