Video playback and social foraging: simulated companions produce the group size effect in nutmeg mannikins

The use of video playbacks may provide a promising technique for the study of social behaviour because it allows experimenters to present a diverse set of behavioural patterns while precisely controlling what the observer experiences. However, in order to validate this technique for social foraging contexts, we must first show that video playbacks can effectively simulate foraging in the presence of foraging groups. A well-documented behavioural response of group-living animals to an increase in group size is a decline in individual levels of vigilance coupled with an increase in foraging rate: the so-called group size effect. We investigated this in captive nutmeg mannikins, Lonchura punctulata, by noting the vigilance and foraging behaviour of focal birds exposed to different numbers of either real or video-simulated companions. Similar patterns of changes in scanning and foraging were observed with changes in both real and simulated group sizes; the birds increased their feeding rate and decreased the time devoted to scanning. The video playback technique therefore provides an effective and appropriate technique for investigating social foraging questions.