Chick provisioning by the Yellow-nosed Albatross Diomedea chlororhynchos: response of foraging effort to experimentally increased costs and demands

We examined the provisioning strategy of a long-lived seabird to test the p rediction from life-history theory that adults should preferentially alloca te resources towards their own needs rather than towards their offspring, a nd to test the abilities of adults to regulate provisioning according to th e chick needs. The individual provisioning behaviour of Yellow-nosed Albatr osses Diomedea chlororhynchos was studied, costs of flight being increased by adding a weight handicap to foraging parents, and needs of the chicks be ing increased by induced regurgitation (underfed chicks) or decreased by fo od supplementation (overfed chicks). Control birds were found to regulate p rovisioning in relation to the nutritional status of the chick and to the m ass of the adult. As a result of increased foraging costs, and possibly of reduced foraging ability, handicapped adults spent more time foraging and d elivered smaller meals. Unlike control birds, they were unable to regulate provisioning and lost slightly more mass than control birds, but they had s imilar survival to the next breeding season. The behaviour of parents reari ng underfed chicks was similar to that of control birds, but adults rearing overfed chicks delivered smaller meals, at the same frequency as control b irds. Thus, although parent Yellow-nosed Albatrosses can perceive the nutri tional status of the chick and regulate provisioning accordingly, they are unable to increase the provisioning rate significantly. They primarily keep resources for themselves, their own body condition determining the level o f investment in the chick. Most albatrosses and petrels behave so that prim arily adult body condition is protected often at the expense of chick provi sioning. Regulation abilities differ between species probably according to several factors such as foraging strategies, distance to feeding zones or b ody size.