Social Behavior and Life History
Kob have few strong social bonds, but females can live in herds numbering in the thousands. They move more and are more social than territorial males. Females are at the front of the daily movements to water. Individuals learn where to go from their mothers. However, in more densely populated herds, the females will take their signals from other females. Males are also present in the migratory herds and will follow the females. All-males herds may number in the hundreds and accompany females as they travel during dry season.
The social and reproductive organization of kob can vary. When in average or low population densities, males establish conventional territories and do not travel much. Adult males try to establish their territories in the best habitat available, which are inhabited by herds of females and their young. Herds are fluid and change in size and structure as individuals travel to find green vegetation. Nonterritorial males, particularly young males, live in bachelor herds and are segregated from the females by the territorial males. On floodplains, where kob are densely populated, around two-thirds of the territorial males establish traditional territories, while the rest live in clustered territories known as leks. These clusters are sometimes smaller than a single traditional territory. Lek clusters are located on patches of short grass or bare ground within comparably tall grassland. As such, these territories have little to no value other than to the males that reside in them. About 8-9 of every 10 females visit leks to mate, trading spacing and food for mating success. Females and bachelor males live in large herds of up to 2000 and move through the leks, which are surrounded by high-quailty grass and are near waterholes and commonly travelled routes.
Conflicts between territorial Ugandan kob (K. k. thomasi) are usually settled with ritual and rarely actual fighting, whether in conventional territories or leks. A male usually needs only to walk in an erect posture towards the intruder to displace him. Neighboring males in leks do the same thing when they encounter their borders. Lek-holding white-eared kobs fight more often. Ugandan kob do sometimes sustain serious or fatal injuries, especially when control of a territory is at stake. Fights usually involve the combatants clashing, pressing and twisting each other with their horns head-on. However, a neighbor may attack from the rear or side. In lek clusters, the most dominant males occupy the center. The number of males in the center of a lek cluster ranges from three to seven, and their leks are the most clustered and they monopolize copulations with estrous females. Replacement of males in leks are much more common than in traditional territores, and most males are able to stay in the centre positions for only a day or two and rarely up to a week. This is largely due to intense competition and because most males leave their territories to feed and drink. Centrally located males reduce their chances of being replaced by leaving to feed during periods of relative calmness, yet they are not able to get enough food and water and have to eventually leave their leks. However, a male can gain enough energy after a week or two, and try to take back his position. At every lek cluster, males are always waiting take or retake a central lek. Males in traditional territories are able to stay for at least a year or two.
Females have their first ovulation at 13–14 month old and have 20–26 day intervals between estrous cycles until they are inseminated. Males from traditional territories and leks have different courtship strategies. Males of traditional territories will herd females and keep them in their territories. Lek males try to do the same, but usually fail. They have to rely on advertising themselves. Kob courtship may last as few as two minutes, and copulation may only last a few seconds. At leks, a female may mate up to 20 times with at least one of the central males in a day. After an eight-month gestation period and giving birth, estrus may commence 21–64 days later. For their first month, calves hide in dense vegetation. Mother and calf can identify each other by their noses. As they get older, calves gather into crèches. When they are three to four months old, the young enter the females' herds and stay with mothers until six to seven months, by which time they are weaned. When they mature, males join bachelors groups.
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