Afr. J . E d . 1992, Volume 30, pages 301-308

Population characteristics of dorcas gazelles in Morocco

CHRIS 0. LOGGERS Montana Cooperative Wildl$e Research Unit, University of Montana, Missoula. M T 59812, U.S.A.

Summary Characteristics used to identify sex and age classes of the dorcas gazelle (Gazella dorcas L.) population at the M’Sabih Talda Reserve in Morocco are described. Counts indicated about 190 animals during the dry season and 210 during the wet season. Densities were at least seven animals > 12 months old/km2 and 9.6 gazelles of all ages/km2. Herd composition was about 60% adults, 13% juveniles, and 25% fawns (animals < 12 months old). Fawn/adult female ratios peaked at 0.92. Average age at death of adults, estimated by tooth cementum layers, was 5.4 years for females and 4.2 for males; longevity for both females and males was 9 years.

Key words: age, dorcas gazelle, Morocco, population

R h m C On dkcrit les caractkristiques utiliskes pour dkterminer le sexe et les classes d’lge de la population de gazelles dorcas (Gazella dorcas L.) de la Rkserve de M’Sabih Talda, au Maroc. Les comptages indiquaient environ 190 animaux pendant la saison scche et 210 pendant la saison des pluies. La densitk Ctait d’au moins sept animaux de plus de douze mois/km2, et de 9,6 gazelles de tous lges/km2. La harde se composait d’environ 60% d’adultes, 13% de juveniles et 25% de faons (jeunes de moins de 12 mois). Le quotient faons/femelles adultes culminait a 0,92. L’lge moyen de la mort des adultes, estimk d’aprb les couches de ckment dentaire, Ctait de 5,4 ans pour les femelles et de 4,2 ans pour les mdles. La longCvitC tant des miles que des femelles Ctait de 9 ans.

Introduction Though dorcas gazelle (Gazella dorcas L.) is the most widely distributed of all the gazelles, scant literature is available on densities, composition of, or factors affecting their populations (Valverde, 1957; Mendelssohn, 1974; Baharav, 1980, 1982; Essghaier, 1981, Yom-Tov & Ilani, 1987; Grettenberger, 1987). Dorcas gazelles once roamed all plains areas of Morocco (Loggers, Thkvenot & Aulagnier, 1992). Populations exist east and south of the Atlas Mountains, but over- harvesting and habitat destruction have reduced numbers in Morocco’s interior to one population on and around the M’Sabih Talda (Sidi Chiker) Gazelle Reserve in the Haouz plains 55 km north-west of Marrakech (Fig. 1). This paper describes (a) age classes of dorcas gazelle (b) the size, and age and sex structure of the population and (c) natality, longevity and causes of mortality of the M’Sabih Talda population.

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Study area The 1987 ha Reserve consists of small gullies that cut through gently rolling hills covered by the grass Stipa retorta and dotted by shrubs (Loggers, 1991). Gullies merge into two 10-m wide oueds (intermittent streams) about 2.5 km apart. The climate is semi-arid: erratic rains fall between November and March; temperatures range from 40°C in July and August to near 0°C in January. The oueds are dry in summer. The Reserve was established in 1952 and by 1956 had been surrounded by a barbed wire fence, through which the gazelles could pass. The Reserve is managed by the Moroccan Department of Waters and Forests who estimated that the population was about 200 animals (M. Bougrine, pers. comm.). The gazelles are the only large mammal that permanently inhabited the Reserve: shepherds illegally grazed their flocks there and wild boar (Sus scrofa L.) were seen in 1987.

Methods Population data I attempted a count of the animals each month from June 1985 to March 1987. The Reserve was sectioned into three units of approximately the same size, based on topographic features. Each area was traversed on foot or on motorcycle. One to all units were counted in a day (count data). Data on sex ratios, social groups and natality were also gathered during observations (from observation data) of territorial males. The fawn crop was estimated from the fawn/adult female ratio (from observation data) and the number of adult females rather than the number of fawns (from count data) because young gazelle fawns ‘lie out’ (Walther, 1973, 1984). Lying out periods for captive dorcas gazelles are 2-6 weeks, during which they are suckled in 0.5-5 min bouts three to five times a day (Walther, 1968). Counts made during lying out periods may underestimate the fawn crop.

IdentiJication of age classes and sex Age classes based on body size and horn structure were chosen to identify life history stages. Classes were fawns (0-12 months), juveniles (12-18 months for females, and until adult horn shape was reached for males), and adults (animals capable of breeding). Classes were based on Hvidberg-Hansen & De Vos (1971), Robinette & Archer (1971) and Walther (1973) for Thomson’s gazelle (G. thomsonii Gunther) and were developed from observations of animals on the reserve and in the Moroccan National Zoo, Temara. Field observations were made with a x 15-45 telescope.

Fawns are visibly smaller than any age group and their horns cannot be consistently seen at viewing distances of more than about 150 m until they are over 6 months old. When they near 12 months, their backs remain lower than those of adult females and their horns are about half as long as their ears.

Juveniles were separated by sex. Body size of juvenile females is about three quarters that of an adult. By 18 months, the back nearly reaches that of adult females, though the body is less stout and the neck thinner. Horns of juvenile females are slim and hooked slightly inward, whereas horns of juvenile males are prominently ringed at the base and the tips hooked sharply inward. By 18 months, the horns of both sexes are about the same length as the ears. Males were classified as juveniles until their horns reached the adult stage at an estimated 30-36 months.

Dorcas gazelles in Morocco 303

Fig. 1. Location of M’Sabih Talla (Sidi Chiker) Reserve, Morocco.

Fig. 2. Female (left) and male perineum patterns used to determine sex

Sex in juveniles and adults was determined by horns, urination/defaecation posture, and perineum pattern (Fig. 2). Horns of all gazelle females are much thinner and shorter than those of males (Estes, 1991). Horns of adult dorcas females are longer than an ear length and lack prominent rings. Those of adult dorcas males are ringed and lyrate.

Females squatted to urinate. If they defaecated after urinating, they began while squatting, rose to a standing position, and often walked, leaving a trailingline of pellets. Male dorcas gazelles adopted urination and defaecation postures charac- teristic ofAntilopinae (Walther, 1984). The shape of the black perineum against the

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Table 1. Estimated size of dorcas gazelle population on the M’Sabih Talla Reserve, Morocco

Other Juv. Juv. Adult Territorial adult Min.

Date < 12 mo.* females males females males males Unidentified** estimate

Sep 1986 52 15 11-12 57 25-32 14-18 10 190 Jan-Feb 1987 51 9 10 59 3 5 3 7 33-35 8 207

+Calculated number usingaverage animal < 12 months old/adult female ratios of 0.9 in September, 1986,

**Contains adult and juvenile females, and males about 18 months old. and 0.9 in January/February, 1987.

white rump patch was sex-specific in juveniles and adults (Fig. 2). In males the anus forms a horizontal bar beneath the tail; in females the perineum includes the vulva and appears as a wide ‘T’. This pattern was confirmed by dead animals found on the Reserve and by close-range observations of dorcas gazelles at the Moroccan National Zoo and the US. National Zoo, Washington, D.C. This pattern also appears in fawns.

Aging by tooth cementum layers A whole tooth from each skull found on the Reserve was collected for analysis by L. Stevens of Fort Collins, Colorado, U S A . Incisors were preferred but if absent or fractured, I substituted a premolar or molar. Robinette and Archer’s (1971) data on tooth replacement in Thornson’s gazelle indicate that molars erupt at 2-10 months of age and that deciduous incisors and premolars are replaced at 12-15 months. One light/dark ring was assumed to mark the annual wet/dry cycle (Erickson & Seliger 1969). I added 12 months for incisors and premolars to estimate replacement dates.

Parasites Fresh faeces from 1 1 animals were collected, stored in formalin, and examined by C. Furley of Bekesbourne, Kent, U.K., to determine parasite egg load levels.

Results and discussion Population data Animals were least disturbed by enclosed vehicles and most by people on foot. Humans or feral dogs disturbed counts during all but the September 1986 and January/February 1987 attempts. I estimated 190 animals in September and 207 in January/February (Table 1). Densities were at least 9.6 km-2 and 10.4 kmP2 for September and January/February. Minimum densities excluding animals c 12 months old were 6.9 km-2 in September and 7.9 km-2 in January/February. Densities were similar to those reported from other areas: 16 km-2 on the T6ntrC National Nature Reserve, Niger (Grettenberger, 1987) and 4.6-7-9 animals > 12 months old/km2 on the Hai-Bar Reserve, Israel (Baharav, 1980).

The population’s age structure of about 60% adults, 13% juveniles and 25% fawns varied little by season or year (Table 2). The juvenile male class contained a low proportion of the population.

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Table 2. Dorcas gazelle age class proportions for count and daily observation data on the M’Sabih Talia Reserve, Morocco

Date Animals < 12 Unidentified

months old Juveniles Adults animals

Nov-Jan 1985/86 0.20 0.20 0.58 0.02 May-Sep 1986 0.23 0.18 0.59 0 Sep I986 count 0.26 0.12 0.57 0.05 Dec-Jan 1986/87 0.28 0.09 0.62 0.0 1 Jan-Feb 1987 count 0.26 0.08 0.62 0.04

Sex ratios from count data for animals > 12 months old decreased from 1.3 females/male during September 1986 to 0.8 females/male during January/ February 1987. Ratios from observation data were 1.1 females/male in June-September and 0.8 females/male in November-February. Small groups ( c 5 animals) of gazelles were seen on forest management areas near the Reserve. These animals probably moved onto the Reserve when livestock grazing on those areas began in late autumn and left after grazing was prohibited in May. Female/male ratios of 1.5 in a herd of 1235 dorcas gazelle in Niger (Grettenberger, 1987) and about 3 in Israel (Table 3a) are similar to female-biased ratios reported for other bovids (Dasmann & Mossman, 1962; Estes, 1967; Spinage, 1974; Wilson & Hirst, 1977).

Dorcas gazelles do not produce twins (Furley, 1986). Fawns were born mainly during late October and March, although a neonate was seen in late August. Dorcas gazelles at the Moroccan National Zoo give birth throughout the year (B. Haddane, pers. comm.). In Niger births occurred from November to January with a peak in November (Grettenberger, 1987). Newby (1978) observed births year- round in Chad with a peak in September and a smaller peak in January. On the reserve ratios from count data (0.9 1 fawns/adult female) were similar to those from observation data (0.92) in September. The January/February count data ratio, 3 months after the parturition peak, was lower (0.83) than that from observation data (0.90).

Fawns comprised 17% of the population at the Hai Bar Reserve, Israel (Baharav, 1980) but those data suffer from the difficulty of counting animals < 12 months old. For each year’s count, more subadult males (12-23 months) were tallied than the previous year’s number of male fawns. I recalculated Baharav’s data, assuming sexual parity at birth, female calving at 24 months, and no mor- tality between the subadult males and the previous year’s fawns (Tables 3b-c). Resulting fawn/adult female ratios rose from 0-18-0.45 to 0.64-1.06. The M’Sabih Talia Reserve’s fawn/adult female ratio of 0.9 suggests high survival of fawns or productivity of > 1 fawn/year. Gestation in dorcas gazelle is 5 - 5 4 months (Furley, 1986); loss of a fawn would shorten the cycle if it affected the doe’s estrous. Mountain gazelles in Israel produce fawns on average every 9.5 months (Mendelssohn, 1974). Social groups. Females live in groups (‘nursery groups’ of Estes, 1967) consisting of adult females and their fawns, juvenile females and juvenile males less

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Table 3. (a) Total dorcas gazelle numbers from the Hai-Bar Reserve, Israel, (b) adjusted total numbers, and (c) adjusted ratios (after Baharav, 1980). Subadult males are 12-23 months old

(a)

Female Male Total Adult Subadult Adult Total Fawns/ Year <12mo. <12mo. < l 2 m o . females males males gazelles adult female

I972 4 3 7 21 4 8 40 0.34 1973 8 5 13 29 9 13 64 0.43 1974 9 5 13 29 9 13 64 0.45 1975 4 2 6 34 9 8 57 0.18 1976 10 4 14 31 8 7 60 0.45

(b)

Subadult Adult Fawns/ Year Fawns females females adult female

I972 18 4 17 I .06 I973 20 9 20 1 .oo I974 18 10 19 0.69 1975 16 9 25 0.64 1976 20 8 23 0.87

Animals < 12 Sub- Year months old adults Adults

1972 0.35 0.16 0.49 1973 0.28 0.25 0.46 1974 0.26 0.29 0.45 1975 0.24 0.27 0.49 1976 0.30 0.24 0.45

than about 18 months old. Though female groups ranged over the territories of more than one male, they 'were most frequently found within the territory of a particular male. When accompanied by a territorial male, female groups averaged 1.4 fawns (range 1-5) and 2.5 females of reproductive age (range 1-8). Lone adult females were often seen.

Males live either as lone territorial males or as bachelors. Bachelors were found singly or in herds of up to ten. Youngest members of the herds were about 18 months old, the age at which, when in the female group, they begin to be harassed by territorial males.

The female groups watched during observations of territorial males rarely lost and never gained a permanent female member other than an offspring. Temporary associations of males and females formed when bachelors encountered a female group that was not attended by a territorial male. Bachelors attempted to court the females, but none was observed to successfully mount. Large herds, which formed

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Table 4. Number of teeth annuli and attributed age of dorcas Number of Attributed gazelle Animal' Tooth2 annuli age (years)

AM AM AM AM AM AM AM AM AM AM AM AM AF AF

'AM =adult male; AF =adult AF female. AF *M =molar; PM =premolar; AF

M 2 M 4 M 2 M 3 M 3

PM 2 PM 4 PM 3 PM 3 PM 6

I 8 I 3

M 8 M 5

PM 2 PM 8 PM I

2 4 2 3 3 3 5 4 4 I 9 4 8 5 3 9 2

I = incisor.

in response to disturbance by humans or dogs, were used by the reserve guards as an indication of illegal activities. Mountain gazelle in Israel also formed large groups during disturbances (Grau, 1974). Mortality. Apart from humans and dogs, the Reserve's adult gazelles currently have no predators, as these have been eliminated from the Haouz. Nine gazelles are known to have died during the study period. Dogs from nearby villages entered the Reserve regularly and killed a juvenile and adult female and two territorial adult males. One of the males was ill and the other had a broken leg due to a trap injury. A third territorial male and another adult male were illegally trapped. Two 18-month-old males died of unknown causes, and a newborn fawn was killed by a golden eagle (Aguila chrysaetos).

Aging by tooth cementum layers Estimated average age at death was 4.2 years (0 = 2.0, n = 12) for adult males and 5.4 years (0 = 2.7, n = 5) for adult females. Oldest specimens were 9 years for both sexes (Table 4). These estimates are not representative of the adult population as territorial males are more susceptible to being poached with traps placed in dung heaps than are adult females.

Parasites Trichuris ova, a common intestinal worm infecting desert ungulates, was not found. Low levels of nematode ova were found in six animals, and Stragyle ova in one animal.

Acknowledgments I would like to thank L. Stevens for sectioning the teeth and C. Furley for examin- ing parasite ovum levels. This project was supported by the Moroccan Department

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of Waters and Forests and the American Peace Corps. The Frankfurt Zoological Society provided funding under project number 1003/85. Graduate support was received from the United States Fish and Wildlife Service Cooperative Wildlife Research Unit at the University of Montana. Dr B. W. O’Gara made helpful suggestions about the manuscript. I dedicate this paper to the guards of the M’Sabih Talda Reserve.

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(Manuscript accepted 25 February 1992)