The roles of parent and chick in determining feeding rates in Leach's storm-petrel

Leach's storm-petrels rear only one chick per brood, and therefore sibling competition cannot be a factor in the evolutionary maintenance of food-solicitation behaviour. Several experiments were conducted to determine whether solicitation may none the less convery information about level of nutrition and thus influence feeding rate. Chicks were switched among nests at random at 40±1 days of age, approximately 3 weeks prior to the termination of parental feeding. Serial correlations were then calculated between each chick's weight before the switch and its weight during subsequent, age intervals, and between each chick's weight before the switch and that of the foster chick during subsequent age intervals. The results contradicted both chick-solicitation and parental-determination models of feeding. Experimental food deprivation suggested that parents do not respond to undernourishment of their chicks by increasing feeding rate. Furthermore, diet supplementation indicated that the rate at which chicks can process meals, especially their lipid component, may be limited by the assimilatory capacity of the digestive tract. The absence of a direct connection between solicitation and food provisioning in storm-petrels may reflect the low correlation between the recent feeding history of a chick and its subsequent requirements. Although solicitation behaviour may facilitate the transfer of food from the adult to the chick, it either does not convey information about nutritional status, or parents do or parents do not or cannot act upon that information.