An evaluation of the use of regurgitated pellets and skeletal material to quantify the diet of Wedge-tailed Eagles, Aquila audax

Abstract

Analyses of prey remains and regurgitated pellets from nesting sites are often used to document the dietary habits of raptors and, in many studies, the results of both techniques are combined. The current study presents a comparison of the proportional contribution of prey species found in prey remains and pellet samples collected from Wedge-tailed Eagle, Aquila Audax, nests in far western New South Wales. The contribution of most prey classes was found to be comparable between samples; however, some significant discrepancies were observed. Rabbits, Oryctolagus cuniculus, and reptiles were found in significantly lower proportions within the pellet sample than the prey remains sample, while a combined class comprising Goats, Capra hircus, and Sheep, Ovis aries, represented a significantly higher proportion of the pellet sample. Similar discrepancies have been reported in other studies of raptor diet and can be attributed to size differences between prey species, differential digestibility, the regurgitation of pellets away from the nest and differences in the handling and consumption of prey. These results suggest that the combination of prey remains and pellet samples may result in a biased representation of raptor diet and that the results of each analysis should be reported separately. Further bias is introduced by the high probability that double counting of prey items occurs. While the observed discrepancies may appear inconsequential in some cases (e.g. Rabbits), the subsequent use of such data in ecological models (eg predator-prey models) may produce misleading results.