Institution: | 1. Behaviour and Ecology Research Group , School of Biological Sciences, University of Nottingham , NG7 2RD , UK;2. Department of Animal Behaviour , Zoological Institute, University of Copenhagen , Tagensvej 16, DK-2200 , Copenhagen N , Denmark;3. Department of Animal Behaviour , Zoological Institute, University of Copenhagen , Tagensvej 16, DK-2200 , Copenhagen N , Denmark |