Sibling recognition in the rook (Corvus frugilegus )

In this study we tested whether rook siblings were able to recognize each other vocally when 2-2 1 2 months-old and, if so, whether this recognition still persisted about 10 months later. Twelve rook nestlings were hand-reared. Vocal recognition by the young birds (aged 2-2 1 2 months) was tested. The birds responded significantly more frequently to the call of a sibling than to the call of a non-sibling. This indicates that audible cues are at least important for sibling recognition. The individual rooks were thereafter visually isolated, in 12 individual cages, for a further 10 months. The birds were then put together in an aviary and their social relationships studied. Siblings were significantly less aggressive towards each other than towards non-siblings and siblings remained close together significantly more often than non-siblings. The significance of sibling recognition is discussed.