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BiologyThe topi employs two different breeding systems, depending on the density of the population. At low densities, a dominant bull defends a territory that supports two to ten females and their immature offspring (6). The territory is marked using various secretions, including one from glands beneath the eyes (2). However, at high population densities, it is thought to be uneconomical for a male to defend large territories, because of the effort required to exclude others from the area. In these situations, breeding leks are formed instead (8); the topi is one of only four antelopes known to do so (pers). In areas where females regularly congregate, males cluster on traditional breeding grounds (6), competing for mates by posturing and sparring with the horns (2). Most females visit this lek on their day of oestrus and mate with the largest, fittest males (6). Recently, research has shown that in individual females in a high density population mate with an average of four partners, mating with each male approximately 11 times. The fertile period of females lasts only a single day, and during this time females may be pushy and aggressive as they attempt to mate with numerous males to ensure that they become pregnant. Males become exhausted during peaks in mating activity and appear to mate selectively due to sperm depletion (9). Female topi give birth to a single calf after a pregnancy lasting 7.5 to 8 months (6). Topi can reach top speeds of over 70 km/h, but are so curious that they have been known to stand and stare while members of their herd are shot. Natural predators include lions, hyenas, leopards, cheetahs and cape hunting dogs (2). Topi graze on most grass species (5), selecting the lush green leaves from amongst dry grass (6).