Observations on the Diurnal Behaviour of the Redtail Monkey (Cercopithecus ascanius schmidti Matschie) in a Small Forest in Uganda

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Abstract
Extensive(1559 man-hours) observations were carried out in Zika Forest, Mengo District, Uganda, by Africans stationed in various parts of the forest. The redtail has a marked activity rhythm and this rhythm is different in the two forest types. In forest at higher elevations activity peaks occur at approx. sunrise and sunset with little activity between, and in swamp forest there are marked peaks at about 0800 and 1530 hr. Heavy rain inhibits activity and high sun temps. during the middle of the day reduce it. The redtail feeds heavily at dawn, continues feeding through the morning till midday, and feeds again from about 1330 hr. till sunset. The majority of feeding occurred in the raised forest, but the raised forest is not necessarily more important as a source of food than the swamp forest. A list of trees fed upon is given. The size of the social groups varied during the day. The solitary portion of the population varied at different times of day between 7 and 15% of the whole; bands (over 10 monkeys) occurred principally at 0900 hr. and between 1400 and 1600 hr. Sleeping units did not vary in size during any night, but sleeping-trees may change from night to night. When solitary monkeys were excluded from the calculation the mean group-size was 3.8 monkeys. Mean number of adults per young in groups reported with young was 2.09. The probable constitution of the normal family group was one male, one or two females and none, one, or two young. The population of the redtails was approx. 35, giving a density of one monkey per 1.3 acres. The population was not randomly distributed, since areas of high canopy and no understorey growth were little occupied by the redtail. Distr. of the monkeys within the forest varied on different days. Social structure and behavior within a redtail group is not so rigid or defined as that found by Zuckerman in two species of baboon. Results are briefly discussed in the light of the epidemiology of yellow fever.