THE PROBLEM OF CHICK LOSS IN THE SOUTH POLAR SKUA CATHARACTA MACCORMICKI

Hunger releases the aggressive behaviour commonly shown by the first chick of the two-chick brood of the South Polar Skua Catharacta maccormicki. Hunger also releases aggressive behaviour in the second chick, but asynchronous hatching usually restricts this behaviour to the first chick. The degree of hunger experienced by the first chick regulates the intensity of its aggressive behaviour, which in turn affects the second chick's survival. Aggressive behaviour restricts the second chick's access to the nest area and deprives it of parental attention, increasing its susceptibility to starvation, exposure and predation. Weight and age differences between the chicks affect neither the release of aggressive behaviour, nor the survival of the second chick.