Food Delivery to Nestling Storm Petrels: Limitation or Regulation?

Abstract

1. Temporal variation in food delivery to nestling British Storm Petrels Hydrobates pelagicus was examined by repeated overnight weighing, to determine whether provisioning rates were likely to be determined primarily by the availability of food to adults foraging at sea or by the chick's immediate food requirements. 2. The interval between successive feeds was short, indicating a relatively small foraging range. 3. There was a negative correlation between mean daily wind speed (considered to reflect foraging conditions) and the proportion of adults returning to feed their chicks (but not meal size) the following night, but this was heavily dependent on a few extreme values. There was no correlation between wind speed and feeding frequency during more typical weather conditions. 4. Chicks' requirements for body maintenance increased with chick age, up to about 39 days post-hatching. This was paralleled by an increase in the amount of food consumed on nights when adults fed their chicks, but not feeding frequency. 5. There was evidence of regulation of feeding frequency in relation to recent feeding history. 6. The finding that the frequency of feeding visits to the colony appears to be regulated in response to the chick's short-term nutritional requirements implies that the achieved feeding rates are below the limits set by food availability and that the low rates of delivery may not be the result of low availability of food at sea