"Intraspecific Variation in Foraging Patterns of Redtail Monkeys (Cercopithecus ascanius) in the Kakamega Forest, Kenya" by Joel Mwangi Gathua

Joel Mwangi Gathua

Deposited 2000

Abstract
This study examined intraspecific variation in foraging patterns of two neighboring groups of Cercopithecus ascanius that occupied different habitats in a Kenyan rain forest. The two groups were demographically similar, each consisting of about 30 individuals. Behavioral data were collected through all-day follows of the focal groups for 7 days per group per month over an annual cycle. Feeding was scored using the frequency method, and the location (50 in x 50 in quadrat) of feeding monkeys was recorded. Hourly location of the group was noted on the site map, and daily path lengths were thus computed. Plant food abundance was measured by combining monthly phenological scores with the density of major plant resources. Insect abundance was assessed using light traps and sweep nets.

The forest-interior home range (occupied by Group F) provided more fruits and insects (caught in light traps) than that of Group E whose range coincided with an extensive forest edge. There were, however, no differences between the two home ranges in the abundance of immature leaves and insects (measured by sweep nets). Group E's range had more tree and liana species than Group F's range.

The amounts of fruits and insects in the diet was similar in the two groups. However, Group F ate cotyledons (obtained from the forest floor) that were avoided by their counterparts and also consumed more immature leaves. In contrast, Group E ate slightly more gum. Group E used more plant species and species-specific food items than Group F. Even with these differences, overlap between the groups in the plant based diet was considerable. Since the contribution of immature leaves, cotyledons and gum to the overall diet was small, the intergroup variation they caused was minimal and perhaps not biologically meaningful. Both groups consumed their major foods (mostly fruits) out of proportion to their abundance. There were correlations between the abundance of fruits contributing more than 10% in the plant diet and their abundance. For some species-specific food items, consumption was correlated to their abundance.

Ranging patterns differed between the groups. Group F traveled farther per day, used more quadrats per day and per month, and had a larger annual range than Group E. However, the two groups showed parallel variation in daily path lengths during the same months; and indeed, daily travel between the groups was correlated across months, suggesting the same factor(s) may have influenced daily path length in both groups. Group E used some quadrats very frequently (on 80% of days) while Group F did not concentrate on any quadrats so extensively (quadrats were barely used more than 50% of days). Group E used its forest edge quadrats more frequently than those located in the interior part of its range while Group F frequently used the central and northern part of its range. Ranging patterns were not obviously related to dietary variables except for daily path length which was correlated to the amount of fruits in the plant diet.

In summary, the two study groups as well as other Cercopithecus ascanius groups in eastern African forest can be described as frugivorous-insectivorous. The two redtail study groups had high dietary similarity in terms of all items (plant food and prey) and plant parts regardless of plant species used. Both groups used the same items from the plant species they shared. Redtails across eastern Africa varied in their daily travel distances, home range sizes and habitat use. The fact that redtails attempted to maintain high-fruit diets may have influenced the observed variability in ranging patterns.