Experimental analysis of predator and prey detection abilities in rainforest: who has the advantage?

JANSON CHARLES HELMAR; MONZÓN JAVIER; BALDOVINO MARÍA CELIA

BEHAVIOUR

BRILL ACADEMIC PUBLISHERS

Lugar: Leiden; Año: 2014 vol. 151 p. 1491 - 1512

0005-7959

Recent theoretical analyses have shown that anti-predator benefits insocial groups depend on the attack distance of the predator relative to preyspacing within groups.  Both attackdistance and prey spacing depend on the ability of predator and prey to detecteach other.  Previous work on forest predators suggest that manydepend on surprise to ambush their prey, thus we test the hypothesis thatdetection distances by eagles of monkeys are greater than vice versa, despitethe supposed advantages of sociality in facilitating detection of predators byprey.  We used field experiments in the wildto assess detection distances of both raptor predators and their natural monkeyprey.  Live hawk-eagles (Spizaetus), under rehabilitation frominjury, were placed tethered to perches in the home ranges of two habituated wildstudy groups of tufted capuchin monkeys (Cebus[apella] nigritus) in Iguazú National Park, Argentina.  Analysis of video footage of the eaglesduring the approach of capuchin monkey groups allowed us to define the firstmoment of behaviours indicating detection by the eagle; detection behaviours ofthe monkeys near the eagle were recorded observationally by field assistants.  The hawk-eagles always detected the monkeys (averagedistance 31.9m) before the monkeys detected the predators (average distance 9.4m). Predators always initially detected oneor two spatially-peripheral individuals of the prey group.  Distance of detection by the predators (andthus maximum possible attack distances) was significantly less than the preygroup spread of 42-57m.  The shortdetection (and consequent short attack) distance of eagles on monkey prey inthis habitat suggests that early warning of attacking eagles may not be aprimary benefit of grouping in this case.