Seasonal changes in the provisioning behaviour and mass of male and femalewandering albatrosses in relation to the growth of their chick

Procellariiform seabirds have a number of extreme life-history characterist ics in common, in particular low reproductive rates and slow postnatal deve lopment, which are generally assumed to reflect the difficulty in acquiring energy in the marine environment. The wandering albatross (Diomedea exulan s) is a sexually dimorphic species with the longest postnatal growth found in any bird, suggesting severe constraints on provisioning and possible sex -specific strategies of provisioning. We studied the provisioning behaviour and mass changes of male and female parent wandering albatross throughout the 9-months rearing period to examine how each sex adjusts its foraging ef fort in relation to the needs of the chicks and the seasonal changes in foo d availability. The study was carried out on the Crozet Islands, using an a utomated system recording continuously the attendance pattern of parents be tween March and December 1994. During the brooding period when energy requi rements are highest, parents only perform trips of short duration to sea, a nd their body condition deteriorates. When the chick is old enough to be le ft alone, the parents mix short and long foraging trips. The proportion of short trips is very high until July, allowing high rate of food delivery an d rapid growth, and at the same time the body condition of adults improves. From August this proportion declines until fledging in December. As a resu lt, the feeding rate decreases from August and adult condition declines, su ggesting that feeding conditions at sea are better during the first part of the chick-rearing period, i.e. in autumn and winter. Male parents perform more short trips of shorter duration and provide larger meals than females, delivering an estimated total after brooding of 110 kg of food, compared t o 70-80 kg delivered by females. Meal size is inversely related to the body condition of male chicks but not to that of female chicks, suggesting that food delivery is regulated by the adults in response to the condition of t he male chick. Male chicks received larger meals and more food every month than female chicks, and overall it was estimated that they receive, after b rooding, 195 kg of food compared to 180 kg for the female. As a result, mal e chicks have a higher growth rate, attain a higher asymptotic mass, and ar e larger and heavier at fledging than female chicks. However, the differenc es are relatively small between the chicks of each sex and suggest that ene rgy may be used differently between the sexes to maximise fitness. The resu lts of the study suggest that provisioning effort of wandering albatrosses is adjusted by parents in relation to the availability of food, to the ener getic needs of the chick and to the sex of the chick. The adult body mass i s likely to play an important role in the long term for the regulation of p rovisioning, deficits in body mass probably providing the buffer in high po wer-requirement periods.