No abstract

We examined the provisioning strategy of a long-lived seabird to test the prediction from life-history theory that adults should preferentially allocate resources towards their own needs rather than towards their offspring, and to test the abilities of adults to regulate provisioning according to the chick needs. The individual provisioning behaviour of Yellow-nosed Albatrosses Diomedea chlororhynchos was studied, costs of flight being increased by adding a weight handicap to foraging parents, and needs of the chicks being increased by induced regurgitation (underfed chicks) or decreased by food supplementation (overfed chicks). Control birds were found to regulate provisioning in relation to the nutritional status of the chick and to the mass of the adult. As a result of increased foraging costs, and possibly of reduced foraging ability, handicapped adults spent more time foraging and delivered smaller meals. Unlike control birds, they were unable to regulate provisioning and lost slightly more mass than control birds, but they had similar survival to the next breeding season. The behaviour of parents rearing underfed chicks was similar to that of control birds, but adults rearing overfed chicks delivered smaller meals, at the same frequency as control birds. Thus, although parent Yellow-nosed Albatrosses can perceive the nutritional 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 of investment in the chick. Most albatrosses and petrels behave so that primarily adult body condition is protected often at the expense of chick provisioning. Regulation abilities differ between species probably according to several factors such as foraging strategies, distance to feeding zones or body size.Integration of the study of foraging behaviour with the study of life-history strategies (Stearns 1976(Stearns , 1992 permits a better understanding of the evolution of reproductive behaviour (Trivers 1972, Nur 1987. When foraging to provision an offspring, the two constraints on predators searching from a central place are time and energy (Ydenberg et al. 1992). The energy gathered during foraging bouts has to be allocated between present and future reproduction so as to maximize inclusive fitness (Williams 1966).