Fruit Finding by Mangabeys (Lophocebus albigena): Are Monitoring of Fig Trees and Use of Sympatric Frugivore Calls Possible Strategies?

Frugivorous forest primates face a continual challenge to locate ripe fruit due to the poor visibility characterizing a heavily vegetated habitat and the spatial and temporal unpredictability of their fruit sources. We present two hypotheses regarding fruit finding in gray-cheeked mangabeys (Lophocebus albigena). The first hypothesis is that mangabeys monitor nonfruiting fig trees by visiting and checking them for fruit at a higher rate than control trees that do not produce preferred fruit. We test this hypothesis by comparing rates of visitation to focal fig trees and control trees. The second hypothesis is that mangabeys use sympatric frugivore loud calls to locate fruit sources. We test this hypothesis (1) observationally, by comparing the rates at which mangabeys visit calling sites of sympatric frugivores and matched control areas; and (2) experimentally, by following mangabey responses to playbacks of tape-recorded calls: the black-and-white-casqued hornbill (Bycanistes subcylindricus) long call, the great blue turaco (Corythaeola cristata) rattling kok, the adult male mangabey whoopgobble, and the chimpanzee (Pan troglodytes) pant hoot. We tested the hypotheses via data from a single group of mangabeys in the Kibale National Park, Uganda. There is no evidence that mangabeys monitor fig trees for the presence of fruit, but they may use the calls of hornbills to locate fruit. Statistical evidence that mangabeys use conspecific whoopgobbles and chimpanzee pant hoots in fruit finding is lacking, though anecdotal observations suggest this possibility. There is no evidence for use of turaco calls in fruit finding.