False feeding: the trade-off between chick hunger and caregivers needs in cooperative crows

False feeding, where individuals refrain from delivering a food item to a begging dependent young, has been described in several cooperative bird and mammal species, but its function is still unclear. False feeding has been suggested to represent either a deceptive tactic of helpers aimed at showing off provisioning behavior to the rest of the group without paying the costs or a normal provisioning behavior of caregivers mediated by the trade-off between the hunger of the young and caregivers' own conditions. Here, we employed an experimental approach to test whether false feeding in cooperatively breeding carrion crows responds plastically to variations of chicks' and caregivers' needs. In 4 different treatments, we manipulated the hunger of the brood and the conditions of group members by 1) experimentally feeding the chicks, 2) food-supplementing group members during the breeding season or 3) throughout the whole year, and 4) clipping 2 primary feathers from each wing of some individuals to increase the costs of flight. Breeders increased false feeding when the brood was food supplemented (treatment 1) and after their wings were clipped (treatment 4), whereas helpers did not change their false-feeding behavior in response to these treatments. Conversely, helpers decreased false feeding when food was supplemented year-round (treatment 3), whereas fed breeders did not show any significant difference compared with controls. These results indicate that a trade-off between chicks' needs (current reproduction) and caregivers' conditions (future reproduction) modulates the occurrence of false feeding, determining different responses in different group members. Copyright 2010, Oxford University Press.