Responses of breeding Cory's shearwater Calonectris diomedea to experimental manipulation of chick condition

Abstract

We studied the regulation of provisioning in Cory’s shearwater at Selvagem Grande during the chick rearing period. Provisioning was examined in terms of feeding frequency and amount of food delivered to chicks. Two groups of chicks were subjected to short-term contrasting manipulations of their nutritional status: one group of chicks was given a food supplement of about 30 g, and another group was deprived of up to 30 g of food. Adults tending deprived chicks increased the frequency of feeding visits (but not the size of feeds), which resulted in an increase in the net rate of food delivery. At the end of this study, deprived chicks were growing at the same rate as fed chicks. Parents attending fed chick did not change their provisioning rates in response to the treatment. Our results indicate that Cory’s shearwaters are able to adjust their provisioning rate in response to short-term variation in the nutritional status of their chicks. We also examined the change in the begging rate of fed and deprived chicks in response to the treatment. There was no relationship between the begging rate and the condition of chicks, which is taken to be a measure of the chick’s physiological condition, related to its ability to withstand imposed periods of fasting. However, fed chicks decreased their begging rate after the increase in their condition due to supplementary food. Conversely, deprived chicks, which were only able to sustain their condition before the onset of the treatment, maintained high levels of begging. To some extent, these results suggest that parental provisioning can be influenced by the begging behavior of chicks. Key words: Calonectris diomedea, chick provisioning, Cory’s shearwater, experimental manipulation, parental behavior. [Behav Ecol 11:274–281 (2000)]