Using video playback to investigate the social preferences of rooks, Corvus frugilegus

It is important for social animals to be able to discriminate between group members. Much is known about vocal social communication through auditory playback techniques; however, visual information may also be important for conspecific recognition in the absence of auditory cues. Within the visual channel both static and dynamic features may play important roles in individual recognition. Rooks are a social corvid and they live in large colonies and form long- term pair bonds, both requiring the ability to recognize individuals. In this study we investigated whether rooks 'see' a digital image as a representation of a real animal, using visual playback techniques and a new paradigm for assessing social preferences that uses stimuli differing in features such as whether they are live animals, static or video images, or stuffed models. We presented the rooks with two different stimuli of the same category and recorded the amount of time they observed each stimulus. Rooks preferred to look at a live bird, static or video image of a bird, and a stuffed model over an empty compartment. Rooks also showed a clear preference for a strongly affiliated conspecific (e. g. their partner) over a nonaffiliated conspecific. This preference was not apparent when we presented subjects with static images; however, the preference was seen with video, indicating that rooks can recognize individuals in video. We conclude that video playback is a useful technique for investigating rook social behaviour. (C) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.