|
|
Gazella thomsonii, (Photo: Erik A. Drabløs) Cladus: Eukaryota Name Gazella thomsonii Gunther, 1884 Vernacular names
The Thomson's gazelle (Eudorcas thomsonii) is one of the best-known gazelles. It is named after explorer Joseph Thomson and, as a result, is sometimes referred to as a "tommie".[1] It is considered by some to be a subspecies of the Red-fronted Gazelle and was formerly considered a member of the genus Gazella within the subgenus Eudorcas, before Eudorcas was elevated to genus status.[2] Thomson's gazelles can be found in numbers exceeding 500 000[3] in Africa and are recognised as the most common type of gazelle in East Africa.[1] Thomson's gazelles are 52 to 67 cm (20 to 26 in) tall and weigh 13 to 24 kg (29 to 53 lb) (females), 17 to 29 kg (37 to 64 lb) (males). They have light brown coats with white underparts and distinctive black stripes on the sides. Their horns are long and pointed with slight curvature. The white patch on their rump extends to underneath the tail but no further. A mistake sometimes made is the misidentification of Grant's gazelles as Thomson's gazelles. Although some Grant's do have the black stripe running across their sides, the white on their rump always extends above the tail. Ecology Thomson's gazelles live in Africa's savannas and grassland habitats, particularly the Serengeti region of Kenya and Tanzania. It has narrow habitat preferences being confined to short grassland with dry firm footing.[4] It does, however, move into tall grassland and dense woodland during migration.[4] Gazelles are mixed feeders.[4] In the wet seasons, gazelles eat primarily lush green grasses,[5] but during the dry seasons it starts to eat more browse[4][5] particularly foliage, bushes, forbs, and clovers.[4] Thomson's gazelles are dependant on short grass.[5] Their numbers highly concentrated at the beginning of the rains since the grass grows quickly.[5] They follow the larger herbivores like plains zebras and blue wildebeests as they mow down the tall grasses.[5] At this time the gazelles spread out more.[5] In the wild, Thomson's gazelles can live up to 10–15 years. Their major predators are cheetahs, which are able to attain higher speeds, but gazelles can outlast them in long chases and are able to make turns more speedily.[6] This small antelope-gazelle can run very fast, up to 70 kph (43 mph), and zigzag, a peculiarity which often saves it from predators. They are also preyed on by lions, leopards, hyenas, baboons, and crocodiles. A noticeable behaviour of Thomson's gazelles is their bounding leap, known as stotting or pronking, used to startle predators and display strength. Social behavior During the wet season, a time when grass is abundant, adult male gazelles will graze extensively. They spread out more and more and establish breeding territories.[7] Younger males usually spend their time in bachelor groups and are prevented from entering the territories.[8] Females form migratory groups that enter the males' territories, mostly the ones with the highest quality resources.[8] As the female groups pass though and forage, the territorial males may try to herd and are usually successful in preventing single females from leaving but not whole groups.[4][8] Subadult males usually resort to fighting to establish dominance while adults are usually more likely to do rituals.[4] If a bachelor male should be passing through a territorial male's region, the male will chase the offender out of his territory.[4] When patrolling his territory, a male may gore the grass, soil, or a bush with his horns.[9] Males will also mark grass stems with a pre-orbital glands which emit a dark secretion.[4][9] Territories of different males may share a boundary. When territorial males meet at the border of their territories they engage in mock fights in which they rush towards each other as if they are about to clash but they don’t touch.[9] After this, they graze in a frontal position, then in parallel and them in reserve and move away from each other while constantly grazing.[9] These rituals have no "winner" but merely "ratify" the position of the boundaries between the territories.[9] Territorial males usually will not enter another males territory. If a male is chasing an escaping female he will stop the chase if she runs into another territory but the neighboring male will continue the chase.[9] A male gazelle will follow a female and sniff their urinate to find out if she is in estrous, a process known as flehmen. If so, he will continue to court and mount her.[9] Female Thomson's gazelles will leave the herd to give birth to single fawns after a 5–6 month gestation period.[10] They are unusual among ungulates in that they can give birth twice yearly, rather than just once.[5] When birthing, a female gazelle stands in a matter similar to when she is urinating and the newborn fawn drops to the grounds while the umbilical cord tears.[11] The mothers then licks the fawn clean of amniotic fluid and tissues.[11] In addition, it is possible licking also serves to stimulate the fawn’s blood circulation or for the mother to "label" the fawn with her scent so she can distinguish it from other fawns olfactorily.[11] In the first six hours of the fawn’s life, it moves and rests with its mother but eventually turns away from its mother and lies down and hides in the grass.[11] The mother stays in the vicinity of the fawn and returns to nurse it daily. Mother and fawn may spend an hour together walking and such before the fawn goes and lies back down to wait for the next nursing.[11] Mother gazelles may associate with other gazelle mothers.[4] However, the fawns do not gather into "kindergartens".[11] Mother gazelles will defend their young against predators like jackals and baboons but not against larger predators. Sometimes, a female tommie can fend a male baboon off by headbutting him with her horns in order to defend her fawn. As the fawn approaches two months old it spends less time lying out and more time with its mother. Eventually the lying out ends.[11] Around this time the fawn starts eating solid food but continues to seek suckles from its mother.[11] The pair will also join a herd. Young female gazelles may associate with their mothers for as yearlings.[11] Young males may also follow their mothers, however as they reach adolescence they are noticed by territorial males and thus cannot follow their mothers into territories. The mother may follow and stay with him but eventually stops following him when he is driven away and the male will them join a bachelor group.[11] The population estimate is around 550 000. There has been a population decline of 60% from 1978–2005.[12] Threats to Thomson’s gazelles are tourist impacts, habitat modification, fire management, and road development.[3] Surveys have reported steep declines (60-70%) over periods of c. 20 years dating from the late 1970s in several places, including the main strongholds for the species: Serengeti, Masai Mara and Ngorongoro.[3] Thomson's Gazelle occur in a number of protected areas in their range. The core areas of the Serengeti-Mara population are protected by the Serengeti N.P. and Masai Mara N.R., where the only land use allowed is wildlife tourism.[3] ^ a b http://www.awf.org/content/wildlife/detail/thomsonsgazelle Further reading Gazelles and Their Relatives by Fritz Walther (1984) Source: Wikipedia, Wikispecies: All text is available under the terms of the GNU Free Documentation License |
|
