Social Structure and Reproduction
Females and young form herds of up to 200 individuals. When food is plentiful, adult males will establish territories. Females pass through the territories with the best food resources. Territorial males round up any female herds that enter their grounds, and will chase away bachelor males that follow. They will even chase away recently weaned males. A male impala tries to prevent any female from leaving his territory. During the dry seasons, territories are abandoned, as herds must travel farther to find food. Large, mixed tranquil herds of females and males form. Young male impalas which have been made to leave their previous herd form bachelor herds of around 30 individuals. Males that are able to dominate their herd are contenders for assuming control of a territory.
The breeding season of impalas, also called rutting, begins toward the end of the wet season in May. The entire affair typically lasts approximately three weeks. While young are usually born after six to seven months, the mother has the ability to delay giving birth for an additional month if conditions are harsh. When giving birth, a female impala will isolate herself from the herd, despite numerous attempts by the male to keep her in his territory. The impala female will keep the fawn in an isolated spot for a few days or even leave it lying out in hiding for a few days, weeks, or more, before returning to the herd. There, the fawn will join a nursery group and will go to its mother only to nurse or when predators are near. Fawns are suckled for four to six months. Males which mature are forced out of the group and will join bachelor herds.
When frightened or startled, the whole herd starts leaping about to confuse their predator. They can jump distances of more than 10 m (33 ft) and 3 m (9 ft) into the air, impalas will explode in a magnificent spectacle of leaping. Impalas can reach running speeds zig-zag of about 60 km/h (37 mph) on average with the peak on 80 km/h (50 mph), to escape their predators. When escaping from predators, they can release a scent from their glands on their heels, which can help them stay together. This is done by performing a high kick of their hind legs.
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