Rhinoceros auklet developmental responses to moderate food restriction

Abstract

Seabird nestlings are vulnerable to food restriction because their parents may not buffer them from prey shortages. I conducted a captive study to explore how rhinoceros auklet chicks (Cerorhinca monocerata) may cope with food restriction and avoid long-term fitness consequences. I predicted auklet nestlings would be adapted to moderate levels of food-stress, and investigated how morphological allocation, glucocorticoid stress response, and fledging behavior change under conditions of a 50% calorie restriction. I also investigated effects of growth and food restriction on carbon and nitrogen stable isotope ratios ([delta]¹³C and [delta]¹⁵N) in auklet tissues. I found that food-restricted auklets allocated resources heavily toward skeletal growth, most notably toward wingchord growth. Restricted auklets exhibited a muted adrenocortical response, increasing glucocorticoid levels only slightly in response to food restriction. Fledging decision was not affected by restriction, with restricted and well-fed chicks fledging at approximately the same age. Both growth and food restriction caused decreases in [delta]¹⁵N of auklet red blood cells (RBCs), but caused no change in [delta]¹³C. Sampling of free-living auklets revealed that natural levels of variability were low for RBC isotope ratios, indicating that the effects of growth and restriction detected in the captive study are of biological significance.