FEEDING BEHAVIOR, PREY SELECTION, AND BILL SIZE OF PIED AND SOOTY OYSTERCATCHERS IN AUSTRALIA

摘要

We studied the relationships between feeding behavior, prey selection and bill size for sympatric Pied (Haematopus longirostris) and Sooty (H. fuliginosus) Oyster-catchers feeding at Australian intertidal mudflats. Foraging Sooty Oystercatchers used a rapid pecking behavior for a greater proportion of time and used a slow pecking behavior for a lesser proportion of time as compared to Pied Oystercatchers. Within each species males used a rapid pecking behavior for more time and used a slow pecking behavior for less time than females. As rapid pecking was used mainly for the capture of crabs, snails and bivalves while slow pecking was used mainly for the capture of polychaete worms, the diet of Sooty Oystercatchers contained significantly more hard-shelled prey and less soft-bodied prey than Pied Oystercatchers. For each species, males took more hard-shelled prey and fewer worms than females. Thus, species and sexual differences in foraging behavior and prey selection segregated the foraging roles of Pied and Sooty Oystercatchers, potentially reducing competition, facilitating their coexistence. A general pattern for Oystercatchers is that longer bill length is associated with higher percentages of soft-prey in the diet for different species, and for sexes within species. A comparison of bill lengths indicated that in Tasmania Sooty Oystercatchers had longer bills than Pied Oystercatchers and within each species, females had longer bills than males. Thus, our results for species are counter to general expectations while results for sexes are consistent with general patterns.