Thomsons gazelle

Gazella thomsonii

TAXONOMY

Gazella thomsonii Günther, 1884, Kilimanjaro, Kenya.

OTHER COMMON NAMES English: Tommies.

PHYSICAL CHARACTERISTICS

Thomson's gazelles have a head and body length of 3-4 ft (91-122 cm), tail length of 6-8 in (15-20 cm), and weight of 29-66 lb (13-30 kg). Males have a shoulder height of 23-28 in (58-70 cm), and a weight of 37- 66 lb (17-30 kg), while females have a shoulder height of 23-35 in (58-64 cm), and a weight of 29-53 lb (13-24 kg). They have a light reddish brown coat on top, a white belly, a fawn colored stripe underneath, a distinctive black stripe running from the foreleg to the hindquarters, and a white rump patch that extends to the entirely black tail. The uniquely dark side stripes may serve as visual signals to keep the herd together. They have pronounced facial markings. The eyes are rimmed with a white line, which then extends to the nose along the muzzle and above black cheek stripes. A dark finger-like pattern occurs on the inside of the ears. Their sight and sense of hearing are well developed, which lets them scout out a large area. Their dark parallel horns are long and only slightly curved. Males have robust, curved horns with large ridges (rings) encircling them. They can reach 11.5-12.0 in (29.2-30.5 cm) in length and are used exclusively for intra-species fighting. Female horns are shorter and more slender; and are used in order to defend their feeding area, especially when food resources are limited. Because of this excess use of their horns, females often end up with broken or deformed horns, or without horns. They have facial and leg glands for territorial marking and species recognition. This species is the least drought tolerant of all the gazelles.

DISTRIBUTION

Southern and central Kenya, southwestern Ethiopia, northern Tanzania, and southeast Sudan.

HABITAT

They stay primarily in the short grassy plains and savannas where food is most abundant and where the landscape is open enough to allow for the gathering of large herds. They feed and reproduce on the short-grass plains during the rainy season and in the taller grasslands in the drier season.

BEHAVIOR

Thomson's gazelles are both nocturnal and diurnal, but are most active early and late in the day, preferring to rest during the hottest part of the day. They are primarily silent animals. Their primary defense against predators is to run, which they can do very effectively at speeds of 40-50 mph (65-80 kph). They can gracefully leap 10 ft (3 m) into the air, jump 30 ft (9 m) in a single leap, and make turns much faster than can a cheetah, one of its main predators. Thomson's gazelles engage in gaits called "stotting" or "pronking" when playing or alarmed. This action entails bouncing stiff-legged so that all four legs land on the ground together. It is believed that this activity helps them to communicate alarm to each other, to give them a better view of approaching predators, and even to confuse or intimidate predators. They have elongated foot bones and anklebones that gives them their speed. They live in herds up to 200 members but normally associate in groups of 2-20. These groups are loosely based, and can change by the hour. They often migrate in groups numbering in the thousands. Multiple groups are often seen interacting with each other. Territories can range from 6 to 495 acres (2-200 ha) but normally are 25-75 acres (10-30 ha). They are very water-dependent but can become water-independent when necessary. During dry periods, they need to be near a water source, sometimes travelling as much as 100 mi (160 km) to find one. During the breeding season males establish territories in order to secure mating rights with females. Males mark their territories with urine and dung piles, and also with secretions from their pre-orbital glands. Territorial males will tolerate familiar subordinate males in their territories as long as they remain subordinate and do not approach the females. Nonbreeding males form bachelor herds.

FEEDING ECOLOGY AND DIET

Thomson's gazelles graze on short grasses, alfalfa hay, and leaves. They avoid tall grass areas. Almost all of their diet consists of grasses. They get most of the water they need from the grasses they eat.

REPRODUCTIVE BIOLOGY

Polygamous. Thomson's gazelles generally breeds twice a year in parallel with the coming rainy season in late December/early February (short rains) and late June/July (long rains), but reproduction is also dependent on the health of the female and environmental conditions. Females give birth to one baby after a gestation period of 5-6 months. The young coat is mottled darker than the mother's coat, but lightens within 1-2 weeks. Females isolate themselves during the birth of their young in order to strength the fawn, and will remain separated from the herd for the first few weeks of life. Once the offspring can run well enough (within 3-4 weeks), mother and fawn will rejoin the group. The weaning period lasts about four months. Females can become impregnated 2-4 weeks after giving birth. Lifespan in the wild is 10-20 years.

CONSERVATION STATUS

Lower Risk/Conservation Dependent. Predation on this small gazelle is always high; they are preyed upon primarily by cheetahs, but also by lions, hyenas, wild dogs, jackals, honey badgers, crocodiles, and leopards. Smaller predators such as pythons, serval cats, baboons, and birds of prey (such as eagles) will also eat the young. Despite the large numbers and types of predators, Thomson's gazelles can be found in numbers of up to 500,000 in Africa, the most common of the gazelles in east Africa.

SIGNIFICANCE TO HUMANS They are hunted for food and skins. ♦

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