TSESSEBE

Facts

Adult Tsessebe are 150 to 230 cm in length. They are quite large animals, with males weighing 137 kg and females weighing 120 kg, on average. Their horns range from 37 cm for females to 40 cm for males. For males, horn size plays an important role in territory defence and mate attraction, although horn size is not positively correlated with territorial factors of mate selection. Their bodies are chestnut brown. The fronts of their faces and their tail tufts are black; the forelimbs and thigh are greyish or bluish-black. Their hindlimbs are brownish-yellow to yellow and their bellies are white. In the wild, Tsessebe usually live a maximum of 15 years, but in some areas, their average lifespan is drastically decreased due to overhunting and the destruction of habitat.

The most significant difference between the Tsessebe, the southernmost subspecies, and the other Topi subspecies is the incline of the horns, with the Tsessebe having horns which are placed further apart from each other as one moves distally. This has the effect of the space between them having a more lunate profile when seen from a certain angle, as opposed to lyrate, more like that of a Hartebeest. Tsessebe populations show variation as one moves from South Africa to Botswana, with southerly populations having on average the lightest pelage colour, smallest size and the least robust horns. Common Tsessebe do not differ significantly from the Bangweulu Tsessebe, the northernmost population, but in general the populations from that part of Zambia are on average the darkest-coloured and have the most robust horns, although differences are slight and individuals in both populations show variation in these characteristics which almost completely overlap each other.

Tsessebe are social animals. Females form herds composed of six to 10, with their young. After males turn one year of age, they are ejected from the herd and form bachelor herds that can be as large as 30 young bulls. Territorial adult bulls form herds the same size as young bulls, although the formation of adult bull herds is mainly seen in the formation of a lek. Tsessebe declare their territory through a variety of behaviours. Territorial behaviour includes moving in an erect posture, high-stepping, defecating in a crouch stance, ground-horning, mud packing, shoulder-wiping, and grunting.

The most important aggressive display of territorial dominance is in the horning of the ground. Another far more curious form of territory marking is through the anointing of their foreheads and horns with secretions from glands near their eyes. Tsessebe accomplish this by inserting grass stems into their preorbital glands to coat them with secretion, then waving it around, letting the secretions fall onto their heads and horns. This process is not as commonly seen as ground-horning, nor is its purpose as well known.

Several of their behaviours strike scientists as peculiar. One such behaviour is the habit of sleeping Tsessebe, to rest their mouths on the ground with their horns sticking straight up into the air. Male Tsessebe have also been observed standing in parallel ranks with their eyes closed, bobbing their heads back and forth. These habits are peculiar because scientists have yet to find a proper explanation for their purposes or functions.

Tsessebe found in the Serengeti usually feed in the morning between 8:00 and 9:00 am and in the afternoon after 4:00 pm. The periods before and after feeding are spent resting and digesting or watering during dry seasons. Tsessebe can travel up to 5 km to reach a viable water source. To avoid encounters with territorial males or females, Tsessebe usually travel along territorial borders, though it leaves them open to attacks by Lion and Leopard.

Tsessebe reproduce at a rate of one calf per year per mating couple. Calves reach sexual maturity in two to three and half years. After mating, the gestation period of a Tsessebe cow lasts seven months. The rut, or period when males start competing for females, starts in mid-February and stretches through March. The female oestrous cycle is shorter, but happens in this time.

The breeding process starts with the development of a lek. Leks are established by the congregation of adult males in an area that females visit only for mating. Lekking is of particular interest since the female choice of a mate in the lek area is independent of any direct male influence. Several options are available to explain how females choose a mate, but the most interesting is in the way the male’s group in the middle of a lek.

The grouping of males can appeal to females for several reasons. First, groups of males can protect from predators. Secondly, if males group in an area with a low food supply, it prevents competition between males and females for resources. Finally, the grouping of males provides females with a wider variety of mates to choose from, as they are all located in one central area. Dominant males occupy the centre of the leks, so females are more likely to mate at the centre than at the periphery of the lek. For a male to reach the centre of the lek, he must be strong enough to outcompete other males. Once a male’s territory is established in the middle of the lek, it is maintained for quite a while; even if an area opens up at the centre, males rarely move to fill it unless they can outcompete the large males already present. However, maintaining central lek territory has many physical drawbacks. For example, males are often wounded in the process of defending their territory from Hyena and other males.