Behavioral patterns and communication in feral asses (Equus africanus)

Applied Animal Behaviour Science 60 Ž1998. 125–169

Behavioral patterns and communication in feral asses žEquus africanus / Patricia D. Moehlman

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Box 2031, Arusha, Tanzania

Abstract The behavior of feral populations of the African wild ass Ž Equus africanus . were studied in the Northern Panamint Range of Death Valley National Monument for 20 months from 1970 to 1973 wMoehlman, P.D., 1974. Behavior and ecology of feral asses Ž Equus asinus .. PhD dissertation, University of Wisconsin, Madison, 251 pp.; Moehlman, P.D., 1979. Behavior and ecology of feral asses Ž Equus asinus .. Natl. Geogr. Soc. Res. Reports, 1970: 405–411x. Maintenance behavior is described and behavior sequences that were used in social interactions are quantified by sex and age class. Agonistic, sexual, and greeting behavior patterns are described and analyzed in conjunction with the responses they elicited. Mutual grooming mainly occurred between adult males, and between females and their offspring. Five types of vocalizations were distinguished: brays, grunts, growls, snorts, and whuffles. A second population was studied for 1 month on Ossabaw Island, GA ŽMoehlman, 1979.. This population had more permanent social groups and had a higher rate of mutual grooming and foal social play. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Equids; Feral asses; Behavior patterns; Facial expressions; Postures; Locomotion

1. Introduction Some of the earliest observations on the social behavior of the African wild ass Ž Equus africanus) and other equids were made by Antonius Ž1937. in the Schoenbrunner Zoo. Antonius noted differences in reproductive behavior, postures, and facial expressions between the six equid species that he observed in captivity. At that time only limited observations were available from field studies, but it was thought that African wild asses and their domestic counterparts did not form stable groups. Antonius observed that the African wild ass, Asian ass Ž E. hemionus ., and Grevy’s zebra Ž E. )

Tel.: q255-57-7504; fax: q255-57-8271; e-mail: [email protected]

0168-1591r98r$ - see front matter q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 1 5 9 1 Ž 9 8 . 0 0 1 6 2 - 2

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greÕyi . were similar in their reproductive behavior and males were socially peripheral to female groups, while the wild horse Ž E. ferus przewalskii . and the plains zebra Ž E. burchelli . tended to form harem groups. Only when observations were available from the field, however, was it understood that some of the behaviors that Antonius observed, e.g., African wild assrdomestic ass males driving females to exhaustion and forcing copulations, were aberrant and did not occur in natural situations. Domestic and feral horses have been the subject of the most intensive equid behavioral studies and an extensive literature is available on their maintenance, communication, and social behavior ŽImanishi, 1950; Montgomery, 1957; Feist, 1971; Tyler, 1972; Welsh, 1975; Feist and McCullough, 1975, 1976; Keiper, 1976; Green and Green, 1977; Houpt et al., 1978; Wells and von Goldschmidt-Rothschild, 1979; Asa et al., 1979; Miller and Denniston, 1979; Miller, 1980; Boyd, 1980; Rubenstein, 1981; Waring, 1983; Berger, 1986; Rubenstein, 1986; Duncan, 1992; Rubenstein and Hack, 1992.. The African wild ass has been studied in Ethiopia, Eritrea, and Somalia ŽKlingel, 1977a; Moehlman et al., 1998., but more in-depth research is needed. Feral ass maintenance, communication, and social behavior have been studied in different habitats in North America ŽMoehlman, 1973, 1974, 1979, 1985, 1998; Morgart, 1978; Woodward, 1979; McCort, 1980; Rudman, 1990.. This paper describes the behavior of populations of feral asses that were studied in the Northern Panamint Range of Death Valley National Monument for 20 months from 1970 to 1973 ŽMoehlman, 1974, 1979.. Maintenance behavior is described and behavior sequences tha t were used in social interactions are quantified by sex and age class and analyzed in conjunction with the responses they elicited. A second population was studied for one month on Ossabaw Island, GA ŽMoehlman, 1979. and differences in observed behavior are discussed.

2. Methods The Death Valley population was studied in the Northern Panamint Range of Death Valley National Monument, CA, USA Ž36815X north latitude, 117815X west longitude.. The study started in March 1970 and continued without interruption through August 1971. Further data were taken in May–June 1972 and June 1973 for a total time in the field of 20 months, spanning 3.3 years. Most observations were made at elevations ranging from 1200–2700 m. The Ossabaw population was studied on a 110-km2 island 7.5 km off the coast of Georgia, USA, at approximately 328 north latitude and 838 west longitude. The study period was 1 month in the summer of 1974. Most observations were made on foot, following the feral asses at distances of 30–40 m. It was rarely necessary to use the Nikon 8 = 24 binoculars or Bushnell spotting scope. Night observations were made with the aid of a Starlight Image Intensifier Scope which was loaned by the Smithsonian Institution. Individual identification of feral asses was possible without the use of marking techniques due to their wide range of coat color, white markings, stripe patterns, and scars. Identification cards were made for each individual showing left and right sides

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and a frontal view. The age classes were Ž1. Adult: 2 or more years old, Ž2. Yearling: 1 to 2 years old, and Ž3. Foal: less than 1 year old. The total number of individuals identified in the Death Valley study area was 237. Forty individuals were identified in the Ossabaw Island study area. Data were recorded with a cassette tape recorder and with pen and notebook. Point samples were taken on the activity of each feral ass at 1-min intervals, i.e., instantaneous scan samples ŽAltmann, 1974.. Sampling sessions usually lasted a minimum of 5 to 6 h. Continuous observations were made of social interactions Že.g., all occurrence sampling., the context and sequence in which they occurred, and the individuals involved. A photographic record of individuals and their behavioral acts was made on 35-mm film with a Nikon camera and Nikkor 300 and 500 mm lens. Ten thousand feet Ž3048 m. of color 16-mm film were taken with a Doiflex camera and Angenieux 12 to 240 zoom lens. The 16-mm and 35-mm film were projected onto the rear of a plexiglass plate and postures and facial expressions were traced onto albanene paper. This provided precise information on the components of behavioral interactions. Vocalizations were recorded on a Nagra tape recorder at a speed of 15 ips with an Electro Voice Žmodel 635A. microphone and a parabolic reflector. Immediately following each recording, the emitting individual, context, and subsequent reaction of all individuals was recorded on the same tape. Sound spectrographs were made on a Kay Sonograph model 6061B. Narrow band sonograms were used for analyzing frequencies and wide band sonograms were used for temporal analysis. The spectrum analyzed was 80–8000 Hz.

3. Results 3.1. General maintenance behaÕior 3.1.1. Locomotion The bone structure and musculature of equids is of the cursorial type and is adapted for rapid locomotion in open terrain ŽAlexander, 1968.. In the feral ass, the walk is a symmetrical gait in which the legs on the left side move in a fashion similar to those on the right. Fig. 1A illustrates the sequence of footfalls in the walk. This pattern is similar to that of most ungulates Žright rear, left front, left rear, and right front. and is diagonal in sequence. During the walk, bipedal support is predominantly ipsilateral Žleft front and rear or right front and rear. which is considered more stable than lateral two-leg support ŽDagg and De Vos, 1968.. The trot is a faster gait which is utilized for escape in alarm situations other than close pursuit. The trot is also utilized in precopulatory driving and chases, foal play, and threats. The feral ass has a basic two beat trot with footfall couplets on the diagonal legs. The sequence of footfalls is left front and right rear, right front and left rear ŽFig. 1B.. The feral ass is not observed to pace Žlateral couplets.. The gallop is an asymmetrical gait that was rarely used by feral asses in Death Valley. Among adult individuals it was observed when a territorial male chased a

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Fig. 1. Locomotion in feral asses. ŽA. walk, ŽB. trot, ŽC. gallop.

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non-territorial male away from an estrous female. Such chases could go for distances of up to 2.5 km. This motor pattern was observed in foals in quick short spurts for distances of up to 50 m. The transverse gallop of the feral ass had a footfall sequence of left rear, left front and right rear, right front ŽFig. 1C.. Either the left or the right front hoof can lead Žstretching farther anteriorly., and the leading foot can be changed while in motion.

Fig. 2. Standing postures. ŽA. Standing alert. ŽB. Standing resting.

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3.1.2. Standing The standing posture of feral asses was distinctive in the alarm context. The head was raised and turned with ears forward and toward the intruder. Weight was on all four feet and the animal appeared tensed for action ŽFig. 2A.. Alert posture would often be accompanied by a ‘snort’. 3.1.3. Resting All age and sex classes of feral asses rest in either a standing or lying position. Adult animals spent more of their resting time in the standing posture and in Death Valley during the hot months they were never observed to rest in a lying posture during the daylight hours. This behavior allows better air circulation and may be a way to avoid potential heat stress due to exposure of greater body surface area to the sun as well as heat conduction from the soil. Equids can rest in a standing position because there is a locking action in the leg joints by ligaments such that no muscular action is necessary to maintain the posture of the locked limb ŽGray, 1968.. Similarly, the ligamentum nuchae, which is dorsal to the cervical vertebrae, contains elastin and functions to reduce the muscular energy that would otherwise be expended to hold the head up. When a feral ass rested in the standing position, its neck was almost horizontal, the ears were down and to the side, and the eyes were closed ŽFig. 2B.. Asses often yawned before and after resting periods. Yawning was done with eyes closed, mouth open and lips drawn back from the teeth, lower jaw shifted laterally, muzzle wrinkled, and ears flopped to the side ŽFig. 3.. Yawning was often accompanied by shaking of the head from side to side with ears flapping up and down. After resting, individuals would often stretch by extending a

Fig. 3. Yawning.

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rear leg or convexly arching the back. The ability to sleep in a standing position is probably adaptive for the evasion of predators. Young foals spent the majority of their resting time in the reclining position, with their mothers feeding or standing nearby ŽFig. 4.. Feral asses lay down to rest and to roll. An individual would stand over the area in which it would lie down, with head lowered and almost touching the ground. The front legs were flexed under the forequarters with more weight being placed on one of the sides. The animal then settled on that foreside with head lifted. This movement was followed by the hindquarters touching the ground ŽFig. 5.. In rising, the forelegs were stretched out in front of the animal’s chest and the head and neck were drawn up and back. The front hooves were planted firmly and the animal pushed up and against the hindquarters. After the forequarters were up and the animal was in a sitting position, the hind quarters were pushed up by the hindlegs directly underneath. This action was

Fig. 4. Foal sleeping.

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Fig. 5. Lying down.

braced by the forequarters. This pattern is similar to the description for horses and zebras ŽZannier-Tanner, 1965.. 3.1.4. Feeding Feral asses feed on shrubs, forbs, and grasses and their preferences will depend on palatability and availability. A typical browsing pattern consisted of an individual spending an average of 38.5 s at a bush and then walking one to eight steps Žleft front foot movement equals one step. to the next feeding site ŽMoehlman, 1974.. This pattern of feeding resulted in one individual lightly hedging many plants. Although the feral ass has the dentition for grazing, it also appears to have special adaptations for browsing. The feral ass has a very mobile upper lip and is able to curl it around the thorniest of vegetation. Feral ass skulls have a mid dorsal projection on the premaxilla which may serve as an attachment site for muscles to the upper lip. Feral asses in Death Valley also fed on cactus by pawing heavy, sharp thorns away with a front hoof and then gnawing the fleshy interior of the plant with their upper incisors.

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3.1.5. Drinking Feral asses would stand with their muzzles in the water and drink for periods of up to 290 s. During the hot months, adult feral asses normally drank once a day ŽMoehlman, 1974.. Maloiy Ž1970. reported that domestic asses could survive a water loss of 30% of body weight and in 120 to 300 s could drink enough water Ž24 to 30 l. to restore fluid loss. Young foals Žless than 2 to 3 months. did not drink, although they would dip their muzzles in the water and then toss their heads up and down, shaking water in all directions. During the hot summer months, adults normally drank once in a 24-h period. Females with foals of less than 2 to 3 months of age drank twice to three times as often as other adult members of the population. 3.1.6. Grooming Feral asses were able to scratch almost any portion of their body with their hooves or teeth. Hooves would be used in a back and forth rubbing motion ŽFig. 6A.. Teeth would be used as scrapers with the upper incisors being used in a unidirectional motion. Individuals would occasionally rub a portion of their body against rocks or trees. Dust bathing occurred on patches of bare ground adjacent to trails. An individual would lie down on its side and then roll back and forth several times, often rolling completely over to the opposite side ŽFig. 6B.. The animal would then stand up and usually shake. Social facilitation of rolling was common. Groups of feral asses would approach a dust bowl and then in sequence each would roll. 3.1.7. Elimination Defecation in both males and females was done in a standing posture with the tail held at a 458 angle from the hindquarters, the rear legs braced backward and spread, and the back slightly convex ŽFig. 7A.. Urination posture for males and females was similar. They stood with the rear legs spread and braced back Ž308 to 458., tail lifted, neck almost horizontal, ears half back, and back convex ŽFig. 7B.. Males urinated with their penis sheathed. 3.2. Social behaÕior 3.2.1. Olfactory communication Defecation by one individual was often followed by defecation by other individuals in the immediate area. Territorial males made dung piles along boundaries and within their territories ŽMoehlman, 1974.. Dung piles also occurred along trails and in the vicinity of water sources. An adult male that approached a dung pile might smell the dung ŽFig. 7C. and walk away, but in 46% of the observations Ž n s 87. he responded by pawing the dung, smelling the dung, defecating on the pile, flehmening, andror fighting with another adult male. Adult males also defecated in single deposits Ž n s 42.. On 38% of these occasions they smelled their defecation, pawed it, flehmened, andror urinated on it. Females of all ages showed little interest in dung and simply defecated where they stood, then walked away ŽMoehlman, 1985..

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Fig. 6. Self grooming. ŽA. Scratching, ŽB. rolling.

Urination by an adult male often facilitated urination in sequence by other males on the same spot. Females made virtually no response to urination, either their own or that of another sex or age class. Females in estrus urinated more frequently, and would often urinate after copulation. Male responses were recorded for 40 occasions when females were observed urinating. Flehmen was displayed in 72% of the male responses ŽMoehlman, 1985.. Flehmen posture in feral asses often served as a visual stimulus that was followed by the approach of other males that also smelled the urination spot and flehmened. Males also assumed flehmen posture while urinating, after smelling the

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Fig. 7. Elimination postures. ŽA. Smelling dung. ŽB. Defecating on dung pile. ŽC. Urination.

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ground Žpossibly an old urination spot., after smelling another male’s urine, after mounting andror copulating with a female, after smelling male defecation, and after smelling a female’s genital area. Flehmen consisted of raising the head with the muzzle pointed toward the sky, the upper lip drawn back extensively and puckered, with the upper teeth and gums exposed, and nostrils wrinkled into a longitudinal and closed position ŽFig. 8.. Male asses were observed to inhale deeply before assuming the flehmen posture. Feral ass foals did respond to female urinations, but male foals responded more frequently Ž91% of eleven observations. and only male foals performed flehmen. Yearlings rarely responded to urine, and only males were observed to flehmen ŽMoehlman, 1974, 1985..

Fig. 8. Flehmen. ŽA. Side view, ŽB. frontal view.

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3.2.2. Acoustical communication Feral ass sound signals were both voiced and unvoiced. Voiced sounds were produced by the larynx and could consist of Ža. atonal sounds—a broad frequency band with no pure tones, Žb. pure tonal sounds—one or a few narrow frequency bands, or Žc. harmonic—a series of narrow frequency bands Žpure tones. that were integral multiples. The actual sound is produced by the vibration of the ligamentum vocali, and is modified by the mouthpiece Žcavity of the mouth and its fittings. ŽTembrock, 1963.. The lifting of the head and the stretching of the neck provide a straight channel for the larynx and lungs ŽFig. 9A.. In the formation of long sound sequences typified by inspiration and expiration of air, the sound is reinforced by lateral laryngeal air cushions ŽKeleman, 1963.. Analyses of feral ass sonograms produced five distinct categories: the bray, grunt, growl, whuffle, and snort. The bray, grunt, growl, and whuffle were vocal, and the snort was non-vocal. Of the four vocal sounds, the bray was the most varied and complex. It consisted of a temporal patterning of inhalations and exhalations that were harmonic in structure ŽFig. 10.. The inhalation was usually composed of one to three frequency bands that often exhibited frequency modulation. The exhalation, by contrast, was typically composed of as many as 30 frequency bands and occasionally exhibited frequency modulation. The temporal patterning of the bray was highly variable Žduration of inhalation, interval, duration of exhalation, interval.. Duration of inhalation varied from 0.05 to 0.40 s and the duration of exhalations varied from 0.05 to 2.30 s. Frequency range for the inhalation and exhalation was from 80 to 8000 Hz. However, within one call sequence the inhalation portion of the call was typically of a higher frequency than that of the exhalation. In this description an inhalation-interval–exhalation-interval will be referred to as a stanza. The bray is a loud, long Žduration up to 24 s., heterotypical vocalization that could be heard at a distance of three km. Brays varied in terms of Ž1. temporal patterning, Ž2. frequency bands, range, harmonic structure, and modulation, and Ž3. intensity. Analysis of a sample of 55 brays indicates that these vocalizations were individually specific and therefore potentially useful for individual identification ŽTembrock, 1963, 1968; Moehlman, 1974.. In the Death Valley population, only males brayed. Table 1 indicates the main sources of individuality in feral ass brays. This distinctiveness in terms of sound frequencies and harmonics were consistent for each individual, but temporal patterning and overall intensity would vary with context and physical activity. This long heterotypical vocalization was done Ž1. in the morning, particularly by territorial males at dawn Žthe call could be spontaneous, but was elicited by and did elicit morning calls by other males.; Ž2. by adult males when meeting other feral asses, particularly at watering areas, and was often followed by tactile greetings ŽFig. 9B.; Ž3. by adult males during pre- and post-copulatory behavior ŽFig. 9C.; Ž4. by adult males when they were threatening each other ŽFig. 9A.; and Ž5. by foals when they were separated from their mothers. The foal bray was softer, lower pitched, more irregular, and shorter in duration. Territorial males’ morning calls tended to be composed of more Ž) 15. and longer Ž0.9–1.0 s. stanzas ŽMoehlman, 1974.. In agonistic encounters, the bray often began with a ‘grunt’ or ‘growl’ followed by a very long exhalation Ž2.6 s. and then a series of

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Fig. 9. Braying postures. ŽA. Male bray with head horizontal, ears back, neck stretched horizontal, tail switching Žagonistic context.. ŽB. Male braying as he arrives at the watering area, ears half back Žgreeting context.. ŽC. Male braying as he stands next to an estrous female, ears forward Žreproductive context..

shorter Ž0.4–0.6 s. stanzas of high intensity. In non-antagonistic greeting behavior, the bray was low intensity with stanzas of increasing duration Ž0.8–2.3 s. and ended with a soft atonal ‘whuffle’.

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Fig. 10. Sonogram of an entire bray sequence ŽE sexhalation I s Inhalation..

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Table 1 Comparison of 10 male brays in terms of their frequency bands in exhalations and inhalations Individual Exhalation major frequencies

a42 a86 a36 a41 a96 a85 a48 a69 a126 a154

300, 900, 1200 300, 900, 1200, 1800 1000, 1500, 1750 Ž250, 500, 750. 1200, 1400 Ž400, 800, 1000, 1800. 300, 900, 1200 900, 1800, 2700 300 300 300, 900, 1200 300, 900, 1200 interrupted

Frequency Inhalation major modulation frequencies

Frequency Relative modulation intensity of exhalation ŽE. and inhalation ŽI.

No No No No No Yes No No No No

Yes No No No No Yes Yes Yes Yes

1800 Ž3600. 4200 Ž2100. 2250 Ž4500. 2200, 4400 – 2100, 4200, 6300 1–8 bands, 3800 2000, 4000 2000, 4000 2200, 4400

Equal Equal Equal E more intense E more intense I more intense E more intense E more intense Equal Changes

Ž. s Lower intensity.

These sonograms are only a preliminary investigation of the feral ass bray, but they indicate that individuals have unique and identifiable calls. These calls vary in temporal patterning and intensity with social context and may convey information on motivational state and social relations. The grunt is a short Ž- 0.3 s. atonal vocalization ranging from 80 to 5200 Hz ŽFig. 11.. The growl ŽFig. 12. is also essentially atonal, but is much longer in duration Ž) 0.7 s.. Both vocalizations occur in an agonistic context, and may be single, in succession, or may proceed andror follow a bray. The whuffle ŽFig. 13. is atonal with a limited amount of banding. It varies in duration from 0.1 to 1.5 s and has a frequency range of 80 to 4000 Hz. They are low intensity, soft vocalizations and they are emitted in an approach andror searching context. Females use them when searching for their foals, and males use them when approaching other feral asses. The whuffle appears to serve as an individual distance-reducing vocalization. The snort is nonvocal and is an exhalation through the nostrils. It is atonal with a frequency range of 80 to 7500 Hz and lasts from 0.3 to 0.35 s. It is an abrupt sound with a short carrying distance Ž200 m. and often induced an alert posture in nearby feral asses. A less explosive and more highly pulsated exhalation was used to clear the nostrils. 3.2.3. Agonistic behaÕior The feral ass, similar to the rest of the Equidae, is capable of threatening with both ends. The frontal threat display had a gradation in intensity and posture, ranging from a subtle turning of the head by the sender to adding ears back, head down, approach at fast walk, trot, andror gallop, to mouth open, to actually biting the receiver ŽFig. 14.. The ‘turns towards’ ŽFig. 14A. consisted of a simple bending of the neck so that the sender was looking more directly at the receiver. The majority of such low level threats were made by an adult male to an adult male Ž90.2%, n s 41.. The usual response of the receiver of such a visual signal was to walk away ŽMoehlman, 1974.. When ‘turn

Fig. 11. Sonogram of ‘grunt’ vocalization.

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Fig. 12. Sonogram of ‘growl’ vocalization.

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Fig. 13. Sonogram of ‘whuffle’ vocalization.

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towards’ was coupled with ‘ears back’, the receiver usually walked away, but on one occasion returned the threat. When ‘turn towards’ was combined with ‘ears back’, ‘mouth open’, ‘walk chase’, and ‘trotrrun chase’, the receiver trotted away or a fight ensued. Adult males performed the majority of these frontal threats. Adult females rarely used ‘turn towards’, ‘walk chase’, andror ‘trotrrun chase’. Adult females used ‘ears back’ half as often as adult males and this posture was directed toward adult males in the reproductive context or toward foals in the nursing context. Adult females used ‘mouth open’ as often as adult males, but the threat was usually directed toward their foals in the nursing context. ‘Bite’ was the most intense action of a frontal threat gradation. This aggressive behavior occurred mainly between adult males and was usually directed to the head and neck region, sometimes to the loins and rear legs, and occasionally to an ear. These bites were serious and resulted in wounds, scars, broken ears, and missing portions of ears. Adult females used ‘bite’ half as often as males. Their bites were of lower intensity and directed toward their foals in a nursing context ŽTables 2–7.. Rear threats showed a gradation in intensity similar to frontal threats. The least intense threat was ‘pivot rump’ toward the approaching male; intensity increased with ‘ears back’, backing toward the approaching or standing receiver, lifting one rear hoof inches off the ground, drawing the rear hoof under the belly in preparation for a backward kick, kicking back with one hind hoof, and kicking back with both hind hooves ŽFig. 15.. Only a small portion of ‘kicks’ actually made contact with the receiver. ‘Pivot rump’ was mainly a signal that was sent by adult males to adult males ŽTable 8.. Males usually approached other males frontally, such that if a male was to make a rear threat he must ‘pivot rump’. By contrast, most females were approached from the rear and no pivots were needed. ‘Rear hoof lift’ was the next stage in intensity and was usually combined with ‘ears back’ and ‘head down’. Between males this was usually sufficient to cause the approaching male to jerk his head up and back, and to turn and walk away. By contrast, when a female assumed this posture toward an approaching male, the male pushed against the female’s rump and lifted his head up. This crowding of the male’s chest against the female’s rump could be preparatory to a ‘mount’, and it reduced the probability of the male receiving a hard and forceful kick. ‘Lift kick’ consisted of drawing the hoof 30 cm or more off the ground and lifting the stifle joint. This type of display was included in the ‘kick’ matrix ŽTable 9. but was a low intensity contact. When a female directed a kick toward her foal, 98.3% were low intensity ‘lift kicks’. This occurred only in the nursing context and prevented andror terminated nursing. The lift kick resulted, at most, in the foal’s muzzle being bumped, and the foal usually turned its head away andror walked away. Adult females sent the majority of ‘kicks’ and roughly half of them were directed toward adult males.

Fig. 14. Frontal threats. ŽA. Male with head ‘turned towards’, ‘ears back’ directed to a yearling female Žestrous female nearby.. ŽB. Male with ‘ears back’, head lowered, tail switching, ‘walk chase’ directed at another male. ŽC. Male braying with ‘ears back’, neck and head horizontal, ‘walk chase’ directed at another male. ŽD. Male with head down, ‘ears back’, ‘walk chase’, directed at a female Ž‘driving’..

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Table 2 Sender–receiver matrix for ‘Turns Towards’ by percentages Sender

Receiver Adult male Adult female Yearling male Yearling female Foal % Totals Total Ž N .

Adult male

Adult female

Yearling male

Yearling female

Foal

% Totals

Total ŽN.

90.2 0 0 0 0 2.5 92.7 38

4.9 0 0 0 0 2.4 7.3 3

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

95.1 0 0 0 0 4.9 100.0

39 0 0 0 0 2 41

However, females did not always ‘kick’ approaching males and in only 4% of the ‘kicks’ was contact made. Males were agile in jerking their heads back and these threats rarely resulted in the males moving away. ‘Fights’ were almost entirely between adult males ŽTable 10.. These contests consisted of rearing, biting, kicking, growling, and grunting and ended with one male walking away or a run chase ŽFig. 16.. Fights were very vocal encounters, with both males usually braying before and after making contact, and growling and grunting as they pushed, shoved, reared, and kicked. For all the sound and fury, combatants rarely sustained more than a few scars andror broken ears. 3.2.4. Sexual behaÕior During estrus, females had a distinctive tail posture. The base of the tail was raised and held out from the hindquarters at an angle of approximately 458 ŽFig. 17A.. This tail posture occurred whether or not males were present. Females in estrus urinated frequently and their vulvae were noticeable swollen. Males exhibited a similar tail posture with a less pronounced angle in association with masturbation, reproductive behavior, and threat behavior.

Table 3 Sender–receiver matrix for ‘Ears Back’ by percentages Receiver

Adult male Adult female Yearling male Yearling female Foal % Totals Total Ž N .

Sender Adult male

Adult female

Yearling male

Yearling female

Foal

% Totals

Total ŽN.

54.6 3.6 0.7 0.7 0.7 60.3 264

16.0 0.5 0.2 1.1 18.5 36.3 159

0.7 0 0.2 0 0.2 1.1 5

0.5 0 0 0 0.2 0.7 3

0.5 0.5 0.5 0 0.2 1.6 7

72.1 4.6 1.6 1.8 19.9 100.0

316 20 7 8 87 438

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Table 4 Sender–receiver matrix for ‘Walk Chase’ by percentages Receiver

Adult male Adult female Yearling male Yearling female Foal % Totals Total Ž N .

Sender Adult male

Adult female

Yearling male

Yearling female

Foal

% Totals

Total ŽN.

95.9 0 1.6 0 0 97.5 119

0 0 0 0 0.8 0.8 1

0 0 0 0 0 0 0

0 0 0 0 0 0 0

0.8 0 0.8 0 0 1.6 2

96.7 0 2.5 0 0.8 100.0

118 0 3 0 1 122

Table 5 Sender–receiver matrix for ‘Trot–Run Chase’ by percentages Receiver

Adult male Total Ž N .

Sender Adult male

Adult female

Yearling male

Yearling female

Foal

% Totals

98.6 73

1.4 1

0 0

0 0

0 0

100.0

Total ŽN. 74

Table 6 Sender–receiver matrix for ‘Mouth Open’ by percentages Receiver

Adult male Adult female Yearling male Yearling female Foal % Totals Total N

Sender Adult male

Adult female

Yearling male

Yearling female

Foal

% Totals

Total ŽN.

45.1 1.1 1.1 1.1 0 48.4 44

4.4 0 0 3.3 38.5 46.2 42

0 0 0 0 1.1 1.1 1

0 0 0 0 0 0 0

0 3.3 1.1 0 0 4.4 4

49.5 4.4 2.2 4.4 39.6 100.1

45 4 2 4 36

% Totals

Total ŽN.

52.2 13.0 10.9 2.2 21.7 100.0

24 6 5 1 10 0 46

91

Table 7 Sender–receiver matrix for ‘Bite’ by percentages Receiver

Adult male Adult female Yearling male Yearling female Foal % Totals Total Ž N .

Sender Adult male

Adult female

Yearling male

Yearling female

Foal

50.0 0 4.3 0 0 54.3 25

2.2 0 0 0 21.7 23.9 11

0 6.5 2.2 0 8.7 4

0 0 0 0 0 0

13.0 0 0 0 13.0 6

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Fig. 15. Rear threats. ŽA. Male approaching a male. Sender ‘lift kicks’, ‘turn towards’, and ‘backs ears’. ŽB. Male raises right rear hoof off ground and under his belly in preparation for a ‘kick’, and at the same time raises his stifle joint toward the approaching male’s nose. ŽC. Female ‘kicks’ male with left rear hoof. ŽD. Male kicks at male with both rear hooves.

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Table 8 Sender–receiver matrix for ‘Pivot Rump’ by percentages Receiver

Adult male Adult female % Totals Total Ž N .

Sender Adult male

Adult female

Yearling male

Yearling female

Foal

% Totals

Total ŽN.

80.5 0 80.5 33

17.1 2.4 19.5 8

0 0 0 0

0 0 0 0

0 0 0 0

97.6 2.4 100.0

40 1 41

Precopulatory behavior in feral asses consisted of Ž1. estrous tail posture by the female, Ž2. male approaching the female’s hindquarters, Ž3. male sniffing the female’s genital area andror laying his head on her rump, andror pushing his chest against the female’s rump, Ž4. male flehmening after sniffing the female’s genitals andror female urinating and male smelling the urine spot on the ground and flehmening, Ž5. male driving the female, Ž6. male mounting the female, often several times, both with and without an erection, and Ž7. male copulating with the female ŽFig. 18.. Females were seldom receptive to male reproductive behavior. When a male approached, the female laid her ears back, lowered her head, and usually kicked. Courting males held their heads low and extended the upper lip such that it protruded beyond the lower jaw and was drawn down ŽFig. 17B.. Males occasionally assumed this facial expression when another male threatened to kick them. Females displayed ‘jawing’, a vertical movement Ždown and up. of the lower jaw with lips covering the teeth ŽFig. 18B. when a male laid his head on their rump andror during mounting and copulation. This facial expression is similar to Unterlegenheitsgebarde that has been described for the horse and plains zebra ŽAntonius, 1937; ¨ Trumler, 1959; Zeeb, 1959; Klingel, 1967; Tyler, 1972.. Feral ass males displayed ‘jawing’ when they were mounted by another male, when males greeted nose-to-nose, and occasionally when they received a kick threat from another male. When mounting occurred between males it was done without an erection and appeared to be a dominance interaction with the subordinate animal being the one mounted.

Table 9 Sender–receiver matrix for ‘Kick’ by percentages Receiver

Adult male Adult female Yearling male Foal % Totals Total Ž N .

Sender Adult male

Adult female

Yearling male

Yearling female

Foal

% Totals

Total ŽN.

25.2 0 0 0.5 25.7 52

36.4 0.5 0 27.1 64.0 137

1.4 0 0 0 1.4 3

3.3 0 0.5 0 3.8 11

3.7 0.5 1.0 0 5.1 11

70.1 0.9 1.4 27.6 100.0

150 2 3 59 214

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Table 10 Sender–receiver matrix for ‘Fight’ by percentages Receiver

Adult male Yearling male % Totals Total Ž N .

Sender Adult male

Yearling male

% Totals

Total ŽN.

88.5 1.6 90.2 55

0 9.8 9.8 6

88.5 11.5 100.0

54 7 61

Females displayed a second distinctive facial expression during sexual behavior. When the female was being mounted andror copulated with her mouth might remain closed with lips drawn back ŽFig. 18C.. This facial expression was called Rossigkeitsgesicht and has been described for horses, plains zebras, mountain zebras, Asian asses, and African asses ŽAntonius, 1937; Klingel, 1967; Joubert, 1972; Tyler, 1972.. Females often interrupted mounting and copulatory behavior by walking or bounding out from under the male. If the copulation was completed to ejaculation the male would slide off and the female would walk forward and either stand or start to browse. If the male and female were alone, the male would usually start browsing. If other males were present, the male would threaten andror chase them away. Females usually urinated after copulation. Males present would then smell the urine and flehmen. In two of the 47 observed copulations, the female after copulation pivoted and attempted to bite the male. An estrous female’s offspring often walked or trotted with ‘ears back’ between its mother and the courting male and often ‘kicked’ at him. Adult males were tolerant of foals and moved around them as they continued to pursue the female. No agonistic behavior by males toward foals was observed. If yearling male offspring attempted to interfere, they were threatened and chased away by the courting male. On two occasions, adult females attempted to interfere with a courting pair. The majority of interference occurred on non-territorial areas where males would threat, push, and fight each other for access to an estrous female. Klingel Ž1969a. observed similar behavior in Grevy’s zebras, where fighting occurred between nine males who courted a female for 2 h, and there were no copulations. Among feral asses in Death Valley there was a sufficient dominance hierarchy to allow more dominant males to successfully copulate with females on non-territorial areas ŽMoehlman, 1998.. On Ossabaw Island where feral asses formed stable harem groups, the dominant male performed most of the copulations, but subordinate males also copulated with estrous females ŽMcCort, 1980..

Fig. 16. Male fight. ŽA. Two adult males threaten each other with ‘ears back’. The male on the left is in a more intense posture with his head down. ŽB. Male on the left with ‘ears back’ and ‘mouth open’ attacks the male on the right, who is threatening with ‘ears back’. ŽC. Two males rearing up and threatening with ‘ears back’ and ‘mouth open’. ŽD. Two males rear up with one male ‘ears back’ and ‘mouth open’ and the other with ‘ears back’ and ‘bite’. ŽE. ‘Run chase’ with the sender ‘ears back’ and ‘mouth open’. Receiver runs away with ears half back.

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Fig. 17. ŽA. Tail posture of a female in estrus Žgenitalia swollen.. ŽB. Facial expression of a male approaching a female’s rear end. ŽC. Frontal view of a male’s facial expression as he receives rear threat.

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Fig. 18. Reproductive behavior. ŽA. Male ‘driving’ a female. ŽB. Male mounting a female. ŽC. Facial expression of mounted female, Rossigkeitsgesicht. ŽD. Male copulating with a female. Female is ‘jawing’.

3.2.5. Greeting behaÕior The majority of greetings occurred between adult males ŽTable 11.. Their facial expressions were characterized by ears in a forward position during the approach portion

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Table 11 Sender–receiver matrix for ‘Greetings’ by percentages Receiver

Adult male Adult female Yearling female Foal % Totals Total Ž N .

Sender Adult male

Adult female

Yearling male

Foal

% Totals

Total ŽN.

60.6 2.2 0 11.7 74.4 134

0 1.7 1.1 5.6 8.3 15

0 0.6 0 1.1 1.7 3

5.6 5.0 0 5.0 15.6 28

66.1 9.4 1.1 23.3 100.0

119 17 2 42 180

of the sequence, but then their ears might move to the side position. A typical male greeting consisted of nose-to-nose contact, often followed by nose to genital contact with a ‘lift kick’ Že.g., a low level threat., andror nose-to-anus contact ŽFig. 19.. In 109 recorded greeting sequences, threat andror fight behavior were involved in a third of the greetings ŽMoehlman, 1974.. Many greetings resulted in the subordinate animal jerking his head up and back. ‘Jawing’ was observed three times, and appeared to be a submissive response. A small portion Ž5.5%. of the greetings were followed by mutual grooming. The Ossabaw Island population had stable groups and greeting behavior rarely was observed. The few male-to-male greetings that occurred within groups consisted of the subordinate approaching the dominant and ‘jawing’ to him. 3.2.6. Mutual grooming Mutual grooming consisted of two animals standing parallel, facing opposite directions, and in unison scraping the hide of the other with its upper incisors ŽFig. 20.. In the Death Valley population, adult males had no special grooming partners, but simply groomed with a male with whom they were temporarily associated ŽTable 12.. Adult females groomed less often, and usually with another adult female or their foal. Adult females and males were not observed mutually grooming one another. Foals usually groomed with their mother. In grooming bouts with adults, the foal usually initiated the bout, and the adult initiated change of sides and termination of the bout. When they groomed with an adult, foals groomed the adult’s lower shoulder region Ždue to smaller stature. rather than the more usual adult area of withers, upper shoulder, and back. The Ossabaw Island population had a higher frequency of grooming Žfive times the Death Valley rate per hour.. An additional three categories of grooming partners were seen, e.g., adult male–adult female, adult female–nonoffspring foal, adult male–foal. 3.2.7. Play Play was defined by Hinde Ž1966. as motor patterns that occur in other contexts, but when performed by young animals are characterized by incomplete sequences of varying intensity. Foal play among feral asses consisted of short runs, quick stops, pivots, runs in an opposite direction, leaps, bucks, and kicks ŽFig. 21.. These actions were performed

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Fig. 19. Greeting. ŽA. Two males approaching each other. ŽB. Naso–naso contact. ŽC. Naso–genital greeting.

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Fig. 20. Two males mutually grooming.

near the mother. Foals also ‘played’ with their mothers by rearing up at them, biting their head and neck, and mounting against their side or rump. The mother usually responded by ignoring the foal or walking away. When a foal stopped abruptly in front Table 12 Sender–receiver matrix for ‘Groom’ by percentages Receiver

Adult male Adult female Yearling male Yearling female Foal % Totals Total Ž N .

Sender Adult male

Adult female

Yearling male

Yearling female

Foal

% Totals

Total ŽN.

35.7 0 0 0 0 35.7 35

0 12.2 0 0 0 12.2 12

2.0 0 1.0 0 0 3.1 3

1.0 1.0 0 0 0 2.0 2

1.0 34.7 0 1.0 10.2 46.9 46

39.8 48.0 1.0 1.0 10.2 100.0

39 47 1 1 10 98

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Fig. 21. Foal nursing and play. ŽA. foal attempting to nurse. Mother switches tail, ‘lift kicks’, thus moving the stifle joint toward the foal’s muzzle. ŽB. Foal solitary play: buck, jump, quick stop. ŽC. Foal play: biting mother.

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Fig. 22. Two foals play fighting ŽOssabaw Island, GA.. ŽA. Biting. ŽB. Neck wrestling. ŽC. Rearing up.

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of an adult other than its mother, it was often threatened. This type of solitary play was common during a foal’s first 2 months and persisted until it was about 6 months old. Play with partners did not occur until Death Valley foals were over 12 months of age. This lack of foal social play may have been due to the low rate of association between foals. On Ossabaw Island, one stable group contained two male foals. In addition to solitary play, these two foals engaged in many hours of social play that consisted of rearing, neck wrestling, and biting in slow motion ŽFig. 22.. 4. Discussion and conclusions 4.1. Maintenance behaÕior Basic maintenance behavior, e.g., locomotion, standing, resting, feeding, drinking, grooming, and elimination, in feral asses was similar to that found in most studies of the Equidae. Feral asses in arid habitats tended to spend a higher proportion of their feeding time browsing rather than grazing ŽMoehlman, 1974; Rudman, 1990.. Browse species in southern California arid habitats had high nutrient and mineral content throughout the year, while forbs and grasses were low in protein and crude fat during the dry colder months ŽMcCullough, 1969.. Feral asses were pregnant during the dry cold months and the higher protein and mineral content of browse species could provide the minimum nutritional requirements for late pregnancy ŽNational Research Council, 1978.. Similar to Grevy’s zebras ŽKlingel, 1974., adult feral asses in hot climates rarely lay down to rest. This behavior may be related to potential heat stress due to the exposure of greater body surface area to the sun. In more mesic andror shaded habitats, adults of other equid species Žhorses, plains zebras. often lay down to rest ŽKlingel, 1967; Tyler, 1972.. 4.2. Social behaÕior 4.2.1. Olfactory communication Elimination behavior conveyed postural and olfactory information. Urination by adult feral ass males facilitated urination on the same spot by other males. Females often urinated post-copulation. Adult males performed most of the social responses to urination. A major component of that response was ‘flehmen’. Flehmen was described by Schneider Ž1930, 1931, 1932a,b, 1934. and serves an olfactory function by sucking air into the nostrils, lifting the head and closing the external nares, and forcing the air into the vomeronasal organ ŽEstes, 1972.. As a specialized olfactory receptor, the vomeronasal organ could play a significant role in enabling the male to odor test the urine and to detect the female’s estrous status ŽFraser, 1968.. Houpt and Guida Ž1984. postulated that such a stimulus to the vomeronasal organ could in turn stimulate the hypothalamus to release luteinizing and follicle-stimulating hormones that are important in the production of testosterone and sperm. Thus in addition to providing olfactory information on a female’s reproductive status, this scent communication may be important for normal male sexual behavior ŽHoupt and Guida, 1984.. When males

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urinate or defecate on top of female excretions they may establish their presence and cover andror dilute the female’s scent mark ŽTrumler, 1958.. The presence of male urine may also play a role in intrasexual competition ŽHoupt and Guida, 1984; Moehlman, 1985.. Feral ass populations living in mesic habitats formed single-male and multi-male harem groups ŽMoehlman, 1979; McCort, 1980.. In these stable groups, more dominant males sniffed female urine and urinated on the spot first, followed by subordinate males. Males displayed flehmen in response to estrous female urinations and these urination spots could be the subject of intense competition for access between males ŽMcCort, 1980.. Territorial feral asses made dung piles along boundaries and within their territories. Dung piles probably serve as communication posts and landmarks ŽMoehlman, 1974, 1985.. In mesic habitats where they also had territories, dung piles were located within territories in areas of greatest use and not concentrated along boundaries ŽMcCort, 1980.. McCort experimentally moved dung piles from one territory to another. These foreign dung piles were fought over by resident males, sniffed, and defecated on, and also stimulated flehmen. Male feral asses would also defecate on strange objects in their environment such as new paint blips in the center of a tarmac road or horseshoe crabs ŽMoehlman, 1974; McCort, 1980.. Among feral horses, adult males also are the sex–age class most responsive to female urinations and to dung piles. They respond to female urinations by assuming an exaggerated urination stance with the tail held abnormally high and release urine on the site in short strong spurts ŽFeist and McCullough, 1976.. Females typically ignored their own and others’ urination and defecation. The ontogeny of response to urine stimuli and flehmen has been studied in horses ŽCrowell-Davis and Houpt, 1985.. Male foals performed flehmen more often than female foals, and foals in general performed flehmen more often than adult females. Male foals had the highest frequency of flehmen during weeks 1 to 4 and the rate declined thereafter to week 20. Utilization of dung piles was a prerogative of adult male feral horses. Typical behavior involved smelling, pawing, defecating, and occasionally urinating. The majority of male defecation occurred on dung piles Ž90% of n s 186, Feist and McCullough, 1976.. When two feral horse bands met, the two dominant males might approach each other, smell the dung pile together, both defecate on it, smell the pile, and then fight or separate. Dominant adult males defecated on the eliminations of females and subordinate males. In the Pryor Mountain study area most dung piles were found on or near trails or in proximity to water holes. Feist and McCullough Ž1976. postulated that for this non-territorial population, dung piles and urination sites had visual and olfactory importance in terms of dominance relationships, associations, and information on hormonal state that persisted over time. In the same study area, Turner et al. Ž1981. found that the adult male response to female elimination Žurination and defecation. varied seasonally, with the frequency of response peaking in the breeding season Ž89–93%. and being very low during the non-breeding season Ž1%.. The average number of eliminations did not vary between months. This behavior correlated positively with male plasma androgens and female plasma steroids. Adult male horses under controlled conditions have responded appropriately to estrous behavior by mares that

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have been ovariectomized. Sex steroids from adrenal sources may mediate estrous behavior in female horses ŽAsa et al., 1980.. Rubenstein and Hack Ž1992. in a study of feral horse communication on the Shackleford Banks used dung transplant experiments to determine what olfactory information might be transferred by fecal material. Adult males were able to differentiate between familiar and unfamiliar dung and spent twice as long sniffing strange dung. However, they exhibited no difference in their response to the dung of dominant vs. subordinate males. Dung may provide a scent signature of an individual with whom recent encounters have provided information on relative fighting ability. These dung piles persist for months and occur predominantly in a dominant harem male’s core area. Thus they potentially provide information to intruding bachelor males andror neighboring harem males that the area’s dominant male is in residence and agonistic encounters could be energetically risky ŽRubenstein and Hack, 1992.. Among wild equids, territorial Grevy’s zebra males establish dung piles at the boundaries and within their areas. Ginsberg Ž1988. observed that territorial males’ dung piles tended to occur on trails in their territory that bachelor males used when traveling to and from watering sites. This suggested that the dung piles could serve as a scent mark station by which the territorial male advertised his ownership. African wild asses also have dung piles within their territories, which Klingel Ž1977a. thought functioned as orientation sites for the territorial male. 4.2.2. Acoustical communication Feral asses had five types of vocalization, of which the ‘bray’ was the most complex. In Death Valley territorial males regularly used this vocalization as a morning call, when meeting other adult males in non-territorial areas, in agonistic interactions with other males, and during courtship behavior. Since each individual had a unique bray, this vocalization had the potential to convey important information concerning relative dominance and fighting ability. Among adult males, if a dominant male threatened a braying subordinate male, the latter usually ceased braying. Yearling and young males only brayed when older males were not present or when there was a long chorus of brays by many males. Grevy’s zebras have a similar spacing system and social organization, and territorial males also emit a long heterotypical vocalization similar to the feral ass bray. Klingel Ž1974. postulated that this served as vocal marking of a male’s territory. Ginsberg Ž1988. investigated this further by mapping the occurrence of such vocalizations for seven territorial males. Most serious fights between territorial males occurred in areas where their territories overlapped. Although males did not spend a disproportionate amount of time in these areas, their ‘territorial’ calls were given significantly more frequently in these areas. In 15% of the observed ‘territorial’ calls Ž n s 195., neighborŽs. responded to a call. However, Ginsberg thought that calls were unlikely to be used to express relative social dominance. By contrast, a study on feral horses on the Shackleford Banks indicated that ‘squeal’ vocalizations provided direct information on dominance status regardless of how well the two adult males knew each other. Sonographs showed that dominant male ‘squeals’ began with higher-frequency sounds and were significantly longer in duration ŽRuben-

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stein and Hack, 1992.. Rubenstein and Hack thought that dominant males might thus be using acoustical communication to indicate superior strength. This communication, when coupled with the olfactory signatures at their dung piles, provides a redundant signal to possible competitors. African asses, feral asses, feral horses, Grevy’s zebras, mountain zebras, plains zebras, and Asian asses all have long heterotypical contact calls which appear to be important for individual recognition. In addition, the three equids that are known to form stable harem groups have a ‘squeal’ that is used in male–male greetings and agonistic encounters Žplains zebras, mountain zebras, and feral horses: Klingel, 1968, 1977a,b; Berger, 1986; Penzhorn, 1988; Rubenstein and Hack, 1992.. Similar to feral asses, other equid species also ‘snort’ as an alarm call, and give a low-pitched ‘whuffle’ or ‘nicker’ that is generally emitted in an individual distance-reducing context. 4.2.3. Visual communication Body postures, position of head, ears, neck, tail, and legs, and facial expressions are all utilized by equids to convey visual information of intent and motivational state. The ‘ears back’ threat was first described for the horse by Darwin Ž1872.. He described the ‘ vicious’ appearance which the ‘drawing back and pressure of ears to the head’ gave the horse. The subsequent equid literature has described four major facial expressions. The Rossigkeitsgesicht ŽAntonius, 1937, 1939; Trumler, 1959. or ‘estrous’ face made by females is an exaggerated open and drawn back mouth. The Unterlegenheitsgebarde ¨ or ‘snapping’ or ‘jawing’ is made by both males and females in a submissive context ŽZeeb, 1959.. The Begruflungsgesicht or ‘greeting face’ was described by Antonius ¨ Ž1939. and Trumler Ž1959.. The greeting face was similar to the ‘threat’ face. All of these facial expression have been described for horses ŽTyler, 1972., plains zebras ŽKlingel, 1967, 1977b., Grevy’s zebras ŽKlingel, 1969b, 1974., mountain zebras ŽKlingel, 1968; Joubert, 1972; Penzhorn, 1984, 1988., and feral asses ŽMoehlman, 1974.. More recently Schilder et al. Ž1984. analyzed 20 combinations of the more characteristic and conspicuous facial expressions that were found to occur frequently in the plains zebra. Their review of the literature revealed overlap and inconsistencies in the description of facial expressions in plains zebras. In particular, elements of ‘estrous’ and ‘jawing’ facial expressions were similar and some illustrations also looked like ‘greeting’ faces. In addition, the ‘threat’ face also was very similar to the ‘estrous’ face ŽTrumler, 1959.. Thus they studied the combination of elements in observed expressions and the context in which they occurred. Based on context they used similarity measures and cluster analyses to determine six basic groups of facial expressions, e.g., as follows. Ž1. ‘Ears forward or sideward, pointing head faces’: a ‘play face’ that occurs in a biting but playful context with an extended upper lip, and occasionally in the pursuit of an estrous female. The extended upper lip face has been observed in feral asses ŽFigs. 17 and 18.. Ž2. ‘Ears backward, covered teeth faces’: a ‘threat face’ that is followed by avoidance behavior by the receiver. This facial expression is seen in feral asses in a similar context but may be accompanied by vocalizations, or might simply be ‘ears backward’ with the mouth closed and the head turned toward the receiver. This was a component of many

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agonistic interactions between feral asses ŽFigs. 14 and 16.. Schilder et al. Ž1984. considered the combination of ears back, mouth open, and teeth bared to be part of a biting sequence and hence not a threat face. In feral asses, this would be considered the most intense portion of a ‘threat face’ escalation, as although it was often preparatory to actual biting, it was still part of a threat sequence and did not always culminate in a ‘bite’ ŽFig. 16.. Ž3. ‘Open mouth face’: a ‘greeting face’ in which ears are forward, mouth is open but teeth are covered, and mouth opens and closes. This occurs between adult males of different status, typically in a tense greeting context, and leads to nose-to-nose contact. This face has elements that have been described in Unterlegenheitsgebarde ¨ or ‘jawing’ faces for horses and feral asses ŽTyler, 1972; Moehlman, 1974.. In feral asses, the ‘greeting face’ was usually done with a closed mouth ŽFig. 19.. Ž4. ‘Bared teeth face’: ‘submissive face’ that may occur with ears forward, ears sideways, or ears backward, and is often accompanied by ‘chewing’ movements and lowering of head. Schilder et al. Ž1984. thought that this category encompassed Žgreeting., Unterlegenheitsgebarde Žjawing or snapping., and Begruflungsgesicht ¨ ¨ Rossigkeitsgesicht Žestrous. faces. Their observations indicated that these three expressions formed a continuum of intensity of submissive expression ranging from the least intense Žears forward. to the most intense Žears backward.. In feral asses this was generally true, in that female asses would display ‘jawing’ or ‘snapping’ during precopulatory and copulatory behavior ŽFig. 18B and D.. However, the female feral ass ‘estrous’ face might not involve an open mouth with bared teeth, but rather a closed mouth with lips extremely drawn back ŽFig. 18C.. Ž5. ‘Head lowered, ears backward face’: ‘submissive face’ used almost exclusively by adult females during avoidance behavior. Schilder et al. Ž1984. thought that this might be a variant on ‘ears forward or sideward, pointing head face’ and that the head was held low simply because the individual had been grazing. However, in feral asses it appears to be the least intense part of a continuum involving the ‘bared teeth face’ ŽFig. 18.. Ž6. ‘Head low, ears backward face’: a ‘herding threat’ that occurred exclusively when adult males were herding females. This also occurred in feral asses. Crowell-Davies et al. Ž1985. studied the ontogeny of ‘snapping’ ŽUnterlegenheitsgebarde or jawing. in horses. Their review of the literature revealed that ¨ although it was considered to be a submissive behavior, it did not inhibit aggression by older individuals. Their research indicated that ‘snapping’ was a ritualized nursing behavior that was a displacement behavior in contexts involving conflicting drives or excessive excitation. Snapping was observed in foals within minutes of parturition and during movements preparatory to nursing. Snapping has been described most often as a behavior of young horses Žone to four years of age. and in the foals peaked at 5 to 8 weeks and then declined, even though contact with non-maternal horses increased. Male foals ‘snapped’ at adult males significantly more often than random, which might be part of the continuum of male–male competition that runs from ‘play fighting’ to intense combat for females ŽCrowell-Davies et al., 1985.. Crowell-Davis concluded that snapping might have multiple signaling functions that depend on context, and that it might be a displacement activity derived from nursing behavior.

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The sequence of events in sexual behavior for feral asses was similar to that described for African wild asses and Grevy’s zebras ŽKlingel, 1974, 1977a.. The driving behavior of the courting male has been observed in all of the territorial equid species, but the extreme exhausting driving and forced copulations described by Antonius Ž1937. appear to be atypical and limited to captive situations. Feral asses in Death Valley were unusual in that copulations did occur in non-territorial areas. There was a sufficient dominance hierarchy among non-territorial males to allow the sequential mating of the female. In Grevy’s zebras, when matings were attempted in non-territorial areas, the intra-male fighting was so intense and chaotic that no copulations were possible ŽKlingel, 1974. or were rarely successful ŽGinsberg, 1988.. Greeting behavior in Death Valley feral asses was often tense and one-third of the encounters involved threats andror fights. A few greetings were followed by mutual grooming. On Ossabaw Island where most individuals lived in stable groups, greetings were rare. The sequence of body postures observed in feral asses is similar to that of other equids. When dominant harem males meet in feral horses, plains zebras, and mountain zebras, there is a similar sequence of nose-to-nose contact followed by nose-to-genital contact ŽKlingel, 1967; Feist and McCullough, 1976; Penzhorn, 1988.. The meeting of two harem males has been described as a ‘challenge ritual’, but usually resulted in both males walking away and resuming grazing. Greetings between a harem male and a bachelor usually consisted of nose-to-nose contact only with the subordinate bachelor male ‘jawing’, and occasionally was followed by mutual grooming. By contrast, Death Valley feral asses in their greetings rarely had an open mouth andror jawed. Grevy’s zebras were similar to feral asses in that during greetings their mouths remained closed and no ‘jawing’ was observed ŽKlingel, 1974.. However, feral asses that lived in a mesic climate and had stable groups often exhibited ‘jawing’ in agonistic encounters ŽMcCort, 1980.. Thus it is possible that the frequency of facial expressions may be affected by the social organization and group composition of the equids being studied. Among most equids the intensity of an agonistic encounter seems to be closely correlated with ear position, much as Darwin Ž1872. described. The behaviors that have been described for feral asses are the most conspicuous, and subtle signals of potential significance to individual feral asses may not have been observed and recorded. The subtleties of individual variation have not been explored, but hopefully this work provides a better understanding of the components and context of observed facial expressions and body postures. Mutual grooming in Death Valley feral asses occurred between adult males, adult females, and a female and her offspring. In the Ossabaw Island population, mutual grooming occurred at a rate five times that of feral asses in Death Valley and in addition to the categories of partners already mentioned, adult male and adult female, female and non-offspring foal, and adult male and foal groomed each other. The higher rate and extended compatibility of mutual grooming in the Ossabaw Island location may have been due to stable social groups and a greater presence of ectoparasites. Tyler Ž1972. observed in horses that the highest frequency of mutual grooming occurred in the months when the horses were shedding their hair and also during the hot months when adult females shared shady areas. In equids that form stable groups, all sex–age

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combinations of grooming partners are observed, but females and their offspring mutually groom most frequently. Social play rarely occurs in equids that live in arid climates where groups are temporary and nutrition may be limiting. Feral ass foals in Death Valley engaged in solitary play but never played with a partner until they were 12 months old. On Ossabaw Island, foals were regularly associated, there was abundant grass and ad lib. mother’s milk, and foals spent hours mutually grooming and play fighting. Grevy’s zebra foals were regularly associated, but solitary and social play were very rare during dry conditions when nutrition may have been limiting ŽKlingel, 1974; Becker, 1983.. Under wetter conditions, Grevy’s zebra foal social play was more frequent and similar to that observed in plains zebras and horses ŽRowen, 1992.. In an equid that typically forms stable family groups Žplains zebra., Klingel suggested that the availability of similar age and sex ‘playmates’ might affect dispersal ŽKlingel, 1972a,b.. However, when Berger Ž1986. analyzed this possibility in feral horses, he found that the number of age peers did not affect the age at which a young male dispersed from his natal group. Berger also found that although the dominant harem male rarely played with a son while the son was resident in the natal group. When a father was approached by a son who had become a bachelor male, the father initiated play-fighting significantly more often than with approaching non-offspring males. Berger could not determine if such behavior contributed to the subsequent reproductive success of sons, but it is fascinating behavior nonetheless.

5. Conclusions The behavior patterns and communication of two feral ass populations were studied in an arid ŽDeath Valley, CA. and mesic ŽOssabaw Island, GA. habitat. In Death Valley the only stable groups were mother and offspring, and some males held territories where they had sole access to reproductive females. By contrast, feral asses on Ossabaw Island formed stable single-male and multi-male harem groups. In the arid habitat, probably due to fluid stress, mothers had a high threat rate toward their foals in the nursing context. Aggressive behavior also occurred in the majority of male-to-male greetings. Little male aggression occurred on territories where resident males were clearly dominant. More severe threats and aggressive behavior occurred on non-territorial areas for access to estrous females. Female-to-male aggression was limited to the reproductive context when the male was driving, mounting, andror copulating with the female. These interactions consisted mainly of ‘ears back’ and ‘kick’ threats that rarely culminated in contact. It was only in the reproductive context that the male approached the female to within four m and on most such occasions, the female threatened. In twenty months there was only one observation of a female presenting to a male. By contrast, the Ossabaw Island population exhibited almost no aggressive behavior. In particular, females rarely threatened their foals and the nursing rejection rate was much lower. The few male-to-male greetings also indicated clear dominance as the subordinate always ‘jawed’ to the dominant male, and there was little or no aggression.

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More intense agonistic encounters only occurred between harem males, similar to what has been observed in horses. In the reproductive context, females would place their ‘ears back’ but they did not ‘kick’. They also usually stood for a mounting, rather than walkingrtrotting out from under the male. The pattern of low sociability in Death Valley was also seen in social grooming behavior. In particular, it was rare for females to mutually groom, and it did not occur between males and females. On Ossabaw Island grooming was much more frequent and all categories of sex and age groups social groomed. Social play followed a similar pattern, in that it was rare in Death Valley but frequent in the stable social groups on Ossabaw Island. These two populations exhibited most of the behavior patterns found within the Equidae. However, the frequency and intensity of behavioral components were different and were consistent with the type of social organization. Although feral asses normally display low sociability, they do exhibit behavioral plasticity and can form stable social groups. Ecological constraints may be critical to the expression of behavior and the formation of social groups.

Acknowledgements The research was supported by grant 144-A255 from the National Science Foundation. The National Geographic Society provided photographic equipment and financial assistance for the months spent in the field. The Smithsonian Institution provided a starlight image intensifier scope. The United States National Park Service provided housing during most of my initial 18-month study period. I thank Mrs. Eleanor Torrey West for her support and permission to work on Ossabaw Island. The Wildlife Conservation Society provided financial support for the written portion of the work. Tasha, the Siberian husky, was a faithful companion and able finder of feral asses. I thank two anonymous reviewers whose critiques and suggestions greatly improved this manuscript.

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