Conspecific presence makes exploiting cryptic prey more difficult in wild-caught nutmeg mannikins

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 naïve 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 foraging 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.