Grant's gazelle

Taxonomy and genetics

Grant's gazelle is more genetically related to Soemmerring's gazelle (N. soemmerringii) and Thomson's gazelle (Eudorcas thomsonii) with Soemmering’s gazelle being the closest relative of the two species. Grant's gazelle shows high genetic variation among its populations, though there is no geographic isolation. The differentiation of the species may have evolved during repeated expansion and contraction of arid habitats during the late Pleistocene era in which populations were possibly isolated. Grant's gazelle was formerly considered a member of the genus Gazella within the subgenus Nanger before Nanger was elevated to genus status.

Subspecies

Listed alphabetically.

Description

The Grant's gazelle stands 75–95 cm (30–37 in) at the shoulder. The females weigh from 35 to 50 kg (77 to 110 lb) and males from 50 to 80 kg (110 to 180 lb). Its coat is a beige orange on the back with a white belly. The Grant's gazelle looks similar to a Thomson's gazelle, except it is much larger and has lyre-shaped horns which are stout at the base, clearly ringed, and measuring 45–81 cm (18–32 in) long. The subspecies are segregated by different morphological characters, such as horn shape and slight differences in coat colour. These differences are not indicative of ecological separation as with some species. Grant's gazelles are extremely fast; they can run 80 km/h (50 mph), but larger males do not exceed 72 km/h (45 mph).

Ecology and behaviour

The Grant's gazelle is found in East Africa and lives in open grass plains and is frequently found in shrublands; it avoids areas with high grass where the visibility of predators is compromised. They also occur in semiarid areas and are relatively well adapted to dry areas, relying on more browse or leafy material during dry seasons to supplement their intake of water. They are migratory animals, but travel in the opposite direction of most of the other ungulates, such as Thomson's gazelles, zebras, and wildebeest, which are more water dependent. They can subsist on vegetation in waterless, semiarid areas, where they face little competition.

The most common predators of the Grant's gazelle are cheetahs and wild dogs. Humans also tend to hunt gazelles. In the Serengeti, Grant's gazelle is a prey item for cheetahs, but the Thomson's gazelle is preferred. However, in Nairobi National Park, Grant's gazelle is preferred over Thomson's gazelle, making it an important resource to the cheetah. Jackals are major predators of fawns.

The Grant's gazelle is a gregarious, territorial, and migratory species. The home ranges of does overlap with those of the bucks. Only male gazelles are territorial. Male gazelles will herd all females that cross their territories. When the females are in estrus, they are strongly guarded by the dominant male, which prevents other males from mating with them. Any doe that tries to leave is aggressively herded back. Most of the time, the buck’s simple stance in relation to her is enough to keep the female from leaving.

Bachelor groups are made up of adolescent and bucks not holding territory. Any new members must perform intimidation displays to enter the group. However, bachelor groups tend to be very loose and members can leave whenever they want. The larger, older males with thick horns have the best chance of establishing a territory. Conflicts between adult males are usually solved with intimidation displays. The bucks circle each other and swing their necks from side to side, displaying their neck power. Neck strength is important in an actual fight and the male that cannot keep up yields. Gazelles of nearly equal neck strength are more likely to engage in actual combat. Fighting occurs in young bucks more often than older ones. Dominant bucks can simply run off subordinates rather than having to display to them.

Diet

Grant’s gazelles are generally mixed feeders that both browse and graze. Their average diet consists of 65.8% browse and 34.3% graze. Rainfall in their habitats seems to be the determinant of their diets. The Grant's gazelle's diet may also be responsible for the slow growth rates in the browsed plots. They get most of their moisture from the plants they eat, so they do not often have to drink water. Thus they can stay on the plains long after the rains end. From July to September, gazelles move deep into dense brush and wait for the next rains. They will eat red oats and small, tough plants, which are avoided by the other ungulates. This allows the gazelles to survive in the brush during the dry season. Grant’s gazelles eat mainly dicotyledons during the dry season and grass in the wet season.

Reproduction

Grant’s gazelles sexually mature at 18 months. Territory-holding bucks mate more than ones in bachelor groups. The courting ritual begins with a buck following a doe, waiting for her to urinate. When she does, the male does the Flehmen response to determine if she is in estrus. If she is, he will continue to follow her. The female will lift her tail, signaling she is ready to mate, and the male will mount her. The gestation period for the gazelle lasts for 198 days. Births peak in January and February. A doe will leave her herd and find a well-hidden place to give birth. Afterwards, the female eats the afterbirth and other fluids to keep the fawn clean and scentless. Females that have recently given birth will stay together for protection. The does nurse their fawns four times a day. Fawns are immobile for the first few days, so the mother stays close by. When the fawn can walk, it leaves with its mother to find a herd. Around this time, fawns will associate with one another in peer groups. A gazelle is weaned at six months, but will continue to associate with its mother until adolescence.

Threats and conservation

The Grant’s gazelle is still a common species, despite having been eradicated in certain areas. Major threats have been habitat destruction and poaching. The gazelle’s status as an unthreatened species is dependent on protection of the national parks and reserves where it lives, including Serengeti National Park and Ngorongoro Conservation Area in Tanzania, and Lake Turkana National Parks in Kenya. Estimates of the population range from 140,000 to 350,000. While certain areas have stable populations, overall the population trend is going downward.