Oryx callotis, Thomas, 1892

Don E. Wilson & Russell A. Mittermeier, 2011, Bovidae, Handbook of the Mammals of the World – Volume 2 Hoofed Mammals, Barcelona: Lynx Edicions, pp. 444-779 : 645-646

140.

Fringe-eared Oryx

Oryx callotis

French: Oryx frangé / German: Blschelohr-Oryx / Spanish: Oryx de Kenia

Taxonomy. Oryx callotis Thomas, 1892 ,

Neighborhood of Mount Kilimanjaro.

The Fringe-eared Oryx was formerly considered a subspecies of O. beisa . Although the two have indistinguishable karyotypes (2n = 58), mitochondrial cytochrome b and control region DNA sequences show that O. callotis is significantly divergent from the Beisa Oryx ( O. beisa ) and the Galla Oryx ( O. gallarum ). Monotypic.

Distribution. SE Kenya and NE Tanzania.

The Fringe-eared Oryx is geographically separated from the Galla Oryx by the Tana River and Aberdare Mts in S Kenya. Its range began to spread into the Serengeti in the 1970s.

Descriptive notes. Head-body 153-170 cm, tail 45-50 cm, shoulder height 110-125 cm; weight 167-209 kg (males) and 116-188 kg (females). These measurements are general for the north-eastern African oryx group and should be considered provisional until further information is available for individual species. The Fringe-eared Oryx is darker, duller, and browner than the Galla Oryx . The Fringed-eared Oryx is large and easily distinguished from other oryxes by its sharply pointed ears with black tufts of hair 5.1-7. 6 cm long. The face is deep ocher, except for the white muzzle stripes; there is usually no connection between the nasal band, which extends through the eyes down to the throat, and the median face band. The Fringe-eared Oryx is very compact and muscular, with long, slender legs, a short,stiff, chestnut-colored mane, and a flowing tail. The body is fawn-colored with distinctive black markings. It has a horizontal black band across the flank region, 3.4-4 cm wide, and black tufts of hair above the hooves resembling false hooves. The dorsal stripe is much reduced, only 2.5-3 cm wide, and is usually confined to the rump; if it extends farther forward,it is very faint. Sexes are not strongly dimorphic, but the horns of males and females do differ. Generally, both sexes have long horns that are slightly curved backward. Horns of females are 76-81 cm long and straighter and thinner than those of males, for better defense against predators. Horns of males are shorter but thicker at the base (12-14 cm), permitting twice as much force in intrasexual combat. The tips of the horns are 24-40 cm apart, which is wider than other north-eastern African oryxes. The skull is comparatively broad. Dental formulais 10/3, C0/1,P 3/3, M 3/3 (x2) = 32.

Habitat. Fringe-eared Oryxes thrive in semi-arid grasslands and brushlands and avoid tall grass; habitats are less arid than those used by other oryxes. They occur in areas of Digitaria macroblephara—Panicum coloratum grassland, Acacia tortilis—Commiphora schimperiwoodland, A. stuhlmannii brushland, and Pennisetum mezianum—A. stuhlmanii bushy grassland.

Food and Feeding. Herbivorous, eating mostly grasses, like other oryx species. Stable isotope analysis indicates that the diet of this speciesis as high as 88% grass; only in the dry season do they eat slightly more browse. The short face and dental morphology (wide incisor row and high-crowned molars) of the Fringe-eared Oryx are adapted for picking nutrient-rich parts of coarse grasses. The diet of the Fringe-eared Oryx often contains the grasses Bothriochloa, Brachiaria, Chloris roxburghiana, Cymbopogon pospischilu, and Enneapogon cenchroides. In addition to grasses, it eats Commelina and Indigofera schimperi in the wet season and Pyrenacantha in the dry season. Oryx species are adapted to arid environments and can go long periods without drinking water because of their selective feeding and ability to use metabolic water. Leaves of the shrub Diasperma contain only 1% water during the daytime but 40% water at night, when the Fringe-eared Oryx predominately feeds on them. It also selects succulent species and digs as deep as 20 cm for roots, bulbs, and tubers to maximize water intake. The Fringe-eared Oryx will drink regularly if wateris available. In a controlled study with water provided every other day on the Galana Ranch, Kenya, Fringe-eared Oryxes drank an average of 34 ml of water per kg of body weight per day in the wet season and 56 ml/kg/day in the dry season. Nevertheless, they can go up to a month without water if succulent grasses are available. They require only 15-20% of the daily water that domestic cattle need and have lower water turnover rates than camels and elands. Fringe-eared Oryxes are adapted to high ambient temperatures, and can pant and use evaporative cooling to minimize heat gain, but this can result in water loss. To minimize the need for water, they can allow their body temperature to rise from a normal 35-7°C to 45°C. Other water-saving adaptations include concentrating the urine, absorbing all moisture from the feces, and seeking shade during the hottest periods of the day.

Breeding. Breeding and births occur throughout the year, but young are often more abundant early in the dry season (June-August). Individuals are sexually mature by 18-24 months. The majority of males in a mixed herd have small scrotums, and males with fully developed scrotums are more likely to breed. Sexually receptive females can be found year-round, but territorial males cannot control all receptive females, leaving breeding opportunities for non-territorial males. Courtship begins with the female’s ears back and head low; the male circles and sniffs her anogenital region, testing her urine for indication of estrus. If the female is receptive, the male lifts his forelegs and mounts her with his back legs bent, and his tail held out. The male may nudge the female gently with his muzzle and occasionally rests his chin on her rump. The mating pair may copulate multiple times. Gestation is 8-5-9 months. Females leave their herd to give birth. They hide their neonates for 2-3 weeks and rejoin their herd after 3—4 weeks, perhaps longer. Calves may form creches, with or without adult females. Calves are born with small horns covered with hair. Females may breed again within a few weeks of giving birth and under good conditions produce an offspring every 10-5-11 months. In captivity, oryxes have survived over 23 years.

Activity patterns. The Fringe-eared Oryx alternates feeding and resting/ruminating throughout the day and night. A herd typically grazes from a half hour after daybreak until 10:00 h, rests/ruminates from 10:00 h until 14:00-15:00 h, and then grazes again until sunset, after which it turns to night resting places to bed down at about 20:00 h. Individuals intermittently rest and graze throughout the night. Activity patterns over a 48hour period vary depending on season: 4-6 hours walking, 15-6 hours feeding, 6-1 hours standing, and 21-6 hours lying during the dry season and 3-3 hours walking, 10-4 hours feeding, 12-5 hours standing, and 21-7 hours lying during the wet season. To keep body temperatures from rising, individuals usually seek shade for an average of 1-7 hours from 11:00 h to 15:00 h. Amount of time spent in the shade tends to be higher when forage biomass is high.

Movements, Home range and Social organization. The Fringe-eared Oryx is nomadic, apparently more than the Gemsbok ( O. gazella ). Their movements are driven by rainfall and availability of green vegetation. One herd travelled 17 km in the same direction in a single day, and a bull walked 4 km in an hour. Home ranges of Fringe-eared Oryxes are typically less than 400 km? The highest reported density is 1-4 ind/km* in Galana Ranch in south-eastern Kenya, where optimum rainfall (400-800 mm /year) results in productive grasslands and some woodland savannas. In the late 1970s, there were 6000-8000 Fringe-eared Oryxes on Galana Ranch. Typically, these oryxes occur in herds of 30-40 individuals, of which 70-90% are females. In the wet season, when forage is abundant, groups can be as large as several hundred individuals. Some males form territories of 5-8 km? Bachelor herds are seldom seen, but 11-28% of males may be solitary. Within the mixed herd, there is a linear hierarchy of males based on aggressive interactions. Females rarely have altercations, and outsider females can usuallyjoin a new group, but incoming males have horn-to-horn fights with the dominant male or other males in the herd. Fights among males are of low to medium intensity. The males clash their horns frontally, parallel, or at an acute angle, but do not attempt to gore each other. Fighting techniques include simple head butting, horn pressing, clash fighting, push fighting, and forehead pressing, with fencing and whirling the most common fighting tactics. If a powerful thrust is used, an attacker can displace his opponent 10-30 m. The dominant male sometimes defecates during a dispute, and both challengers may take breaks to graze during the fight, but this only happens if the subordinate male initiates feeding. Movements of herds appear coordinated; if one herd member changes activity, nearby members follow, and soon the whole herd has changed activity. There can be a “pulling” effect;if an individualstarts “marching,” others follow in single file. While marching, the herd is usually led by a female, but not always the same individual, and the dominant male brings up the rear. Males can also control the herd’s movements.

Status and Conservation. Classified as Vulnerable on The IUCN Red List (as O. beisa callotis ). There were an estimated 17,000 Fringe-eared Oryxes in 2008; 60% were in protected areas, and fewer than 10,000 were mature individuals. A 10% population decline is projected to occur over the next three generations (21-24 years). Eventually all Fringe-eared Oryxes may be confined to parts of south-eastern Kenya that are protected from settlement and poaching. In Tanzania, they may eventually be confined to Tarangire National Park and Mkomazi Game Reserve.

Bibliography. Ansell (1972), Estes (1991a, 1991b), Field (1975), Kahurananga (1981), King (1979), Kingdon (1982, 1997), Kumamoto et al. (1999), Leuthold & Leuthold (1975a), Lewis (1978), Masembe et al. (2006), Packer (1983), Price (1978), Roosevelt & Heller (1914), Sponheimer et al (2003), Stanley Price (1985), Stewart & Stewart (1963), Thomas (1892a), Wacher (1988), Walther (1978), Weigl (2005).

Figures

138. Beisa Oryx (Oryx beisa), 139. Galla Oryx (Oryx gallarum), 140. Fringe-eared Oryx (Oryx callotis), 141. Gemsbok (Oryx gazella), 142. Scimitar-horned Oryx (Oryx dammah), 143. Arabian Oryx (Oryx leucoryx)

Distribution. SE Kenya and NE Tanzania . The Fringe-eared Oryx is geographically separated from the Galla Oryx by the Tana River and Aberdare Mts in S Kenya . Its range began to spread into the Serengeti in the 1970s.