Control of provisioning in grey-headed albatrosses (Thalassarche chrysostoma): do adults respond to chick condition?
Recent studies have been equivocal in determining whether long-lived seabirds are able to respond to chick nutritional status and regulate provisioning rates accordingly. With some exceptions, albatrosses and petrels that feed their chicks every 1-3 days seem able to respond to variability in chick condition. In contrast, those with longer overall feeding periodicity and that frequently show a dual foraging strategy, mixing short trips (which most benefit the chick) with longer, pelagic feeding excursions (during which time adults recover lost condition), tend not to regulate provisioning. We used a combined observational and experimental approach to determine whether feeding rates in grey-headed albatrosses (Thalassarche chrysostoma) were determined by parental foraging proficiency and (or) offspring demand. The results indicated that both factors were important. Adults showed consistent differences in provisioning characteristics, but chick satiation and solicitation also influenced the mass of the meal delivered when adults returned. Given a provisioning schedule characterised by relatively frequent colony visits and with no means of assessing the feeding success of their partner in the interim, the adjustment of meal mass upon arrival appears to be a simple means of tailoring prey delivery to changing chick requirements and is likely to be as effective as alternative strategies suggested for other species of Procellariiform.