pelage texture and colour, and the terminal tuft of the tail. The wildebeest have more specialised skull and horn features than the hartebeest. The hartebeest exhibits sexual dimorphism, but only slightly, as both sexes bear horns and have similar body masses. The degree of sexual dimorphism varies by subspecies. Males are 8% heavier than females in Swayne's and Lichtenstein's hartebeest, and 23% heavier in the red hartebeest. In one study, the highest dimorphism was found in skull weight. Another study concluded that the length of the breeding season is a good predictor of dimorphism in pedicle (the bony structures from which the horns grow) height and skull weight, and the best predictor of the horn circumference. Ecology and behaviour Active mainly during daytime, the hartebeest grazes in the early morning and late afternoon, and rests in shade around noon. Gregarious, the species forms herds of up to 300 individuals. Larger numbers gather in places with abundant grass. In 1963, a congregation of 10,000 animals was recorded on the plains near Sekoma Pan in Botswana. However, moving herds are not so cohesive, and tend to disperse frequently. The members of a herd can be divided into four groups: territorial adult males, non-territorial adult males, young males, and the females with their young. The females form groups of five to 12 animals, with four generations of young in the group. Females fight for dominance over the herd. Sparring between males and females is common. At three or four years of age, the males can attempt to take over a territory and its female members. A resident male defends his territory and will fight if provoked. The male marks the border of his territory through defecation. Hartebeest are remarkably alert and cautious animals with highly developed brains. Generally calm in nature, hartebeest can be ferocious when provoked. While feeding, one individual stays on the lookout for danger, often standing on a termite mound to see farther. At times of danger, the whole herd flees in a single file after an individual suddenly starts off. Adult hartebeest are preyed upon by lions, leopards, hyenas and wild dogs; cheetahs and jackals target juveniles. Crocodiles may also prey on hartebeest. The thin long legs of the hartebeest provide for a quick escape in an open habitat; if attacked, the formidable horns are used to ward off the predator. The elevated position of the eyes enables the