The Value of Measuring Food Availability on the Ground for a Semiterrestrial Frugivore, the Tana River Mangabey (Cercocebus galeritus) of Kenya

Collecting phenological data, seasonal availability of plant resources that primates feed on, allows us to understand feeding ecology better. A number of primates are terrestrial or semiterrestrial frugivores, yet phenology is generally measured only in the canopy. I hypothesized that combining measurements of food availability on the ground with canopy measurements would more strongly correlate with diet than canopy measurements alone for a semiterrestrial frugivore, the Tana River mangabey (Cercocebus galeritus). From July 2005 until June 2006, I conducted monthly follows on a mangabey group. Phenology was measured in 105 individuals of their top seven food tree species. I measured canopy phenology on a 0-5 scale and counted fruits in three 1 m(3) areas of the canopy, and measured ground phenology by counting fruits and seeds in four 1 m(2) quadrats under the canopy. I calculated each tree's canopy volume and canopy shadow, and each species' mean fruit weight, mean seed weight, and density. Monthly biomasses were calculated as kilograms per hectare. Spearman correlations were performed between diet contribution and canopy biomass, ground biomass, and total biomass. The hypothesis was not supported for seven species individually or combined. The hypothesis was supported for 3 of 12 diet items, although canopy biomass was also significant for 2 of those items. Two diet items correlated only with ground biomass. Studies of the Tana River mangabey may benefit from measuring ground phenology only for those items eaten exclusively on the ground. Primatologists studying terrestrial or semiterrestrial frugivores should consider feeding height when deciding on phenology methods.