Available online at www.sciencedirect.com Conspecific presence makes exploiting cryptic prey more difficult in wild-caught nutmeg mannikins SABRINA COURANT & LUC-ALAIN GIRALDEAU De ´partement des Sciences Biologiques, Universite ´ du Que ´bec a ` Montre ´al (Received 6 November 2006; initial acceptance 9 January 2007; final acceptance 13 August 2007; published online 28 January 2008; MS. number: A10614R) Solitary predators respond to cryptic prey by adopting counterstrategies such as forming a search image or reducing their search rate. However, the response of group-foraging individuals to cryptic prey remains poorly studied. We investigated the effect of the presence of an experienced or a na € ıve conspecific on the ability of nutmeg mannikins, Lonchura punctulata, to exploit millet seeds presented on cryptic and noncryptic backgrounds. The conspecific’s level of experience did not affect a focal bird’s foraging, so we lumped both experience condition for analysis. The presence of a competitor tended to increase the occurrences of vigilance and food searching, but it did not affect the duration of vigilance. In contrast, foraging on a cryptic background significantly affected foraging by reducing the occurrences of food searching and vigilance, and increasing the latency to eat the first seed as well as the number of detection errors. Background type and competitor presence interacted significantly for searching bout duration, number of seeds eaten and foraging efficiency. In all cases, competitor presence negatively affected forag- ing efficiency under cryptic backgrounds. Finally, the foraging efficiency of individuals that had previously foraged with a competitor on cryptic seeds remained low even after the competitor had been removed. Thus, costs of foraging on cryptic prey may be greater for social foragers than for solitary foragers. Ó 2007 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Keywords: cryptic prey; interference competition; Lonchura punctulata; nutmeg mannikin; search image; social foraging Many species rely on cryptic coloration to elude visual detection by predators (Kettlewell 1955; Endler 1978, 1984). Foraging on cryptic prey increases both the latency of prey detection and the number of detection errors (Lawrence 1985a, b, 1986). Visual predators may, how- ever, learn to improve their ability to distinguish cryptic prey from the background by forming a search image after repeated encounters with cryptic prey (Tinbergen 1960; Dawkins 1971; Pietrewicz & Kamil 1979; Gendron 1986; Lawrence 1986). Alternatively, foragers may increase their detection efficiency by reducing the rate at which they scan the substrate in search of prey (Gendron & Staddon 1983, 1984; Guilford & Dawkins 1987). Both mechanisms make a number of similar predictions concerning the consequences for predators foraging on cryptic prey (Reid & Shettleworth 1992; Plaisted & Mackintosh 1995). Few studies, however, have explored the conse- quences of prey crypticity for group foragers (Barrette & Giraldeau 2006). Foraging in the company of others can either enhance or reduce an individual’s foraging rate. The classic response to increasing group size is an increase in feeding rate accompanied by reduced investments in antipredator vigilance (Elgar & Catterall 1981; Lagory 1986; Lima & Dill 1990; Lima 1998; Lima et al. 1999). Some studies suggest that enhanced foraging rates are due to increased efficiency when companions provide social information (reviewed in: Galef & Giraldeau 2001; Danchin et al. 2005). Other studies have found that reduced foraging rates are caused by exploitation (Schoener 1983; Begon et al. 1990) or interference (Goss-Custard 1980; Cresswell 1997) competition, including kleptoparasitism (Stillman et al. 1996; Triplet et al. 1999), overt aggression (Goldberg et al. 2001; Dubois & Giraldeau 2004) and self-imposed reductions in feeding rates (Va ´squez & Kacelnik 2000; Gauvin & Giraldeau 2004). Correspondence and present address: L.-A. Giraldeau, De ´partement des Sciences Biologiques, Universite ´ du Que ´bec a ` Montre ´al, succursale Centre-ville, Case postale 8888, Montre ´al, Que ´bec H3C 3P8, Canada (email: giraldeau.luc-alain@uqam.ca). S. Courant is now at the De ´partment de Biologie, Universite ´ Laval, pavillon Alexandre-Vachon, Que ´bec, Que ´bec G1K 7P4, Canada. 1101 0003e 3472/08/$32.00/0 Ó 2007 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. ANIMAL BEHAVIOUR, 2008, 75, 1101e1108 doi:10.1016/j.anbehav.2007.08.023