Chick provisioning and parental attendance in Cory's Shearwaters: implications for nestling obesity

Gory's Shearwaters, in common with other species of Procellariiformes, accu mulate large quantities of body fat after hatching. This pattern of develop ment has been related both to temporal variation in feeding conditions arou nd the colony and to stochastic variation in foraging success and food prov isioning by individual parents. Chicks need not necessarily always accept f ood provided by their parents, yet few studies have examined parental atten dance independently of the masses of food fed to chicks overnight. This pap er examines variability in provisioning and growth of nestling Gory's Shear waters over three years between 1991 and 1994, and uses observations of ind ividually marked admits coupled with radio-tracking to examine the nest att endance patterns of individual parents. Chicks were fed on 77% of nights on average, with little temporal variation in food delivery at the level of t he colony. Individual chicks were nonetheless fed highly variably, and this to some extent supports the notion that nestling obesity results from chro nic overfeeding by the parents to reduce the impact of variable food provis ioning at an individual level. Chicks were attended by 1.5 parents overnigh t on average, and chicks were attended but not fed on 16% of occasions. Par ents may have returned on these occasions without any food for the chick, o r the chick may have refused to accept food from the parents. A minority of nests accounted for most of the occasions when a chick was attended but no t fed, and there was evidence to suggest that these chicks were consistentl y heavy for their size. A refusal by these chicks to accept food on some oc casions is consistent with the notion that lipid stores of chicks should be optimized rather than maximized, and this requires further investigation.