Validation of the water offloading technique for diet assessment: an experimental study with Cory's shearwaters (Calonectris diomedea)

We examined the effect of prey type, repeated stomach flushing, digestion time, and meal size on the assessment of dietary intake of captive adult Cory’s shearwaters (Calonectris diomedea). For each of Cory’s shearwaters’ main prey type (fish, cephalopod, and crustacea), we used three different meal sizes and four digestion times, stomach-flushing the birds 1, 4, 8, or 16 h after feeding. On average, fish and cephalopods showed similar percentages of mass recovery (between 23% and 33%), whereas crustaceans showed a recovery about 10–15% greater. Conversely, fish and crustaceans showed similar percentages of items recovered (between 52% and 77%), whereas cephalopods showed about 10–35% greater recovery rates. We found no significant differences in the percentage of individual prey items recovered and the interval between ingestion and recovery, over intervals ranging from 1 to 16 h.