DETERMINANTS OF FEEDING CHASES IN THE CHINSTRAP PENGUIN PYGOSCELIS-ANTARCTICA

Feeding interactions between parents and chicks in pygoscelid penguins are frequently associated with chases. We tested alternative predicti ons derived trom two functional hypotheses proposed to explain feeding chases: (1) the harassment of the parent by two begging, competing ch icks is stressful and makes the parent run away to avoid stress ('hara ssment avoidance hypothesis') and (2) chases are initiated by parents to separate the two chicks before feeding them in order to avoid inter -sibling competition, and thus to increase food transfer efficiency (' efficient food transfer hypothesis'). In an observational study of Chi nstrap Penguins Pygoscelis antarctica during the creche stage, we foun d that feeding chases were initiated in the presence of two begging ch icks independently of their competitive disposition. When the chicks c ompeted, parental visits lasted longer, and parents took longer time t o transfer a given number of feedings, than when there was no competit ion. In chases inducing chick separation, the duration of adult runnin g bouts was determined by the time it Look to separate them. This woul d not be the case if feeding chases were initiated to avoid harassment by two competing chicks. Feeding chases initiated by parents appears to be a behaviour tending to separate the two chicks in order to feed them more efficiently, which results in shortening the time spent by p arents in the colony. Additionally, we found some evidence indicating that through the feeding chases parents could also gain information on the nutritional needs of their chicks.