Vomit or flush? Diet analysis using samples from spntaneous regurgitates or the water-off-load technique

Several methods, each with specific advantages and disadvantages, are frequently used to obtain diet samples from seabirds. The collection of regurgitates (REG) as well as samples from the stomach water-off-load (WOL) or flushing technique are some of the most commonly used approaches. During the Austral breeding season of 2005/06 diet samples from Cape Petrel Daption capense and Snow Petrel Pagodroma nivea were collected at Signy Island, South Orkney Islands, Antarctica. Primarily, diet samples were obtained by stomach flushing but occasionally (8 Snow Petrels and 12 Cape Petrels) birds spontaneously regurgitated their stomach contents before flushing. These regurgitates were sampled completely and stored separately. Afterwards the remainder of the bird’s stomach contents was flushed. By doing so, a comparison could then be made between the REG samples and the total stomach contents (REG+WOL). In the REG samples of both species the fraction of fish was underestimated and the fraction of crustaceans overestimated compared to the REG+WOL samples. This study shows that methodology-specific outcomes are potentially to be expected when doing dietary research. Using REG samples is shown not to be suitable for quantitative assessments of the diets of petrels. The WOL technique, which collects the entire stomach content, suits this purpose better.

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