Size and Composition of Foraging Flights in Two Species of Piscivorous Colonial Birds: Limited Evidence for Intra- or Interspecific Information Transfer

Abstract

Colonial birds must derive benefits from living in conspecific groups and with other species. One possible benefit is that they follow previously successful individuals to foraging sites (information center hypothesis). To test for evidence of intra- and interspecific information transfer, we assessed the group size and composition of flights of double- crested cormorants (Phalacrocorax auritus) and American white pelicans (Pelecanus erythrorhynchos) at two mixed colonies. Flights by solo individuals were the most common outbound type, suggesting that the birds do not immediately follow others. However, the majority of the total number of outbound birds traveled in groups. In comparison, groups in- bound to colonies and flying between feeding locations were large. Regardless of flight direction, groups were almost al- ways largest during the late chick-rearing period. This suggests that groups may have some function, although likely not to share information about foraging-sites. Mixed-species groups in general were rare, so it is unlikely that these birds commonly locate prey by following other species in flight.