Assessing the Diet of the Black Skimmer Through Different Methodologies: Is the Analysis of Pellets Reliable?

Abstract

Two different types of food samples from the Black Skimmer (Rynchops niger) were collected during the non-breeding season: spontaneous regurgitations and pellets. These two samples were analyzed and differed in the number of taxonomic categories represented, the number of fish prey species found and in the estimated size of fish prey. However, key prey were the same and well represented in both types of samples, suggesting that both sources gave accurate information, at least for the main items. Given that collecting pellets involves little effort and low disturbance to the birds, the value of the analysis of pellets to monitor long-term dietary changes in the Black Skimmer and other seabird species of similar size and diet is considerable. Correction factors are proposed to overcome underestimation of the total length and mass of some fish prey species remains found in pellets.