Opportunistic behaviour of white-eyelid mangabeys

White-eyelid mangabeys share a common foraging strategy with mandrills and drills (genus Mandrillus) characterized by rummaging through the leaf litter in search of fallen fruits and invertebrates. Both genera are generalized omnivores noted for their adaptability and opportunistic behaviour. The following three examples highlight the explorative, opportunistic behaviour of white-eyelid mangabeys.

Agile mangabeys (Cercocebus agilis) have been studied at the Mondika and Bai Hokou field sites in Dzanga-Ndoki National Park, Central African Republic, where forest elephants (Loxodonta cyclotis) are present. At both sites, mangabeys have been regularly observed sifting through elephant dung piles to pick out the edible seeds. This seed predation may have an important impact on forest dynamics by counteracting the seed dispersal services provided by forest elephants. Sifting through elephant dung has also been observed when a group of approximately 200 agile mangabeys visited Dzanga Bai, a large forest clearing in the same national park. It is not known how widespread this behaviour is. It would be interesting to know if it also occurs at other sites where mangabeys share their habitat with elephants.

An adult male agile mangabey (Cercocebus agilis) sifting through an elephant dung pile at Bai Hokou.

After the dry season of 2010, large mushrooms of the family Russulales began to appear in mono-dominant forest patches of cursief: Gilbertiodendron trees at Bai Hokou. The agile mangabeys spend on average 5% of their time in this forest type. However, during the two weeks when these mushrooms were highly available, they spent approximately 17% of their time in this forest, specifically to exploit this temporary resource. This permanent large group of 135 individuals, during the study period, could be seen foraging through this open type of forest checking for fresh mushrooms under each leaf on the forest floor. The group spent almost 40% of their foraging time consuming mushrooms. The same opportunistic behaviour has also been observed at Mondika.

Agile mangabeys (Cercocebus agilis) feeding on a mushroom at Bai HokouJuvenile agile mangabey (Cercocebus agilis) feeding on a mushroom at Bai Hokou.

Agile mangabeys (Cercocebus agilis) feeding on mushrooms at Bai Hokou.

Some frog species produce terrestrial foam nests to escape predation by aquatic creatures. They lay their eggs in a gelatinous mass attached to leaves, branches or tree trunks above a surface of water. When the tadpoles have developed to a certain stage, they are washed off by heavy rain. Sooty mangabeys (Cercocebus atys) at Taï in Ivory Coast, are known to feed on the foam nests of two species of frog (Chiromantis rufescens, Hyperolius sp.). Once detected, the mangabeys would scoop out the eggs with their fingers, suck them from the leaf, or swallow the whole leaf. Nests may contain 100 to 200 eggs with a diameter of 2 to 3mm. Frog eggs probably represent a valuable, although opportunistic, protein source and observations suggest that the mangabeys deliberately searched for this food source. They would even jump into the water to harvest foam nests out of reach. Foam nest raiding is also known from samango monkeys (Cercopithecus mitis stuhmanni) in Southern Africa. Similar behaviour is also likely to occur in agile mangabeys (Cercocebus agilis) at Bai Hokou. On two occasions, individuals were seen eating a kind of foam attached to tree roots above water pools created by elephants, although the foam did not appear to contain eggs when checked by the observer. The mangabeys did not show the deliberate searching behaviour observed at Taï, but did spread out the remaining foam on a surface, like mangabeys do at Taï. If anyone could confirm whether this could be a foam nest of a frog species, please leave a reply.

A juvenile agile mangabey (Cercocebus agilis) eating foam at Bai HokouA juvenile agile mangabey (Cercocebus agilis) eating foam at Bai Hokou.

A juvenile agile mangabey (Cercocebus agilis) spreading out the foam at Bai HokouThe result of an agile mangabey (Cercocebus agilis) spreading out the foam.

A juvenile agile mangabey (Cercocebus agilis) eating foam at Bai Hokou.

Key references:
Devreese L. (2011). Many hands make light work. Foraging strategy of agile mangabeys (Cercocebus agilis) exhibiting a permanent large grouping pattern at Bai Hokou, Central African Republic. Master thesis, University of Antwerp, Belgium.

Rödel M-A., Range F., Seppänen J-T. & Noë R. (2002). Caviar in the rain forest: monkeys as frog-spawn predators in Taï National Park, Ivory Coast. J. Trop. Ecol. 18: 289-294.

Shah N. (2003). Foraging strategies in two sympatric mangabey species (Cercocebus agilis and Lophocebus albigena). Ph.D. Thesis, State University of New York, Stony Brook.

Written by Lieven Devreese on December 15, 2013.

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This website is dedicated to the genus Cercocebus. Although white-eyelid mangabeys are known to science since the end of the 18th century (Kerr, 1792), they remain poorly understood because of the challenges associated with studying them in the wild. Cercocebus.be aims to bring information on the taxonomy, distribution, ecology and behaviour of these mysterious primates to you, scientist, naturalist or enthusiast.