Weak niche partitioning by migrating shorebirds in a single-food-type environment

Abstract

This study examined foraging niche partitioning among coexisting species of shorebirds on a sandy beach dominated by a single food type, Horseshoe Crab ( Limulus polyphemus) eggs, where use of foraging microhabitats of limited variety is temporarily restricted due to tidal cycle. The major goal of the study was to examine whether co-occurring species differed in selection of foraging microhabitats and use of feeding techniques. Ruddy Turnstone ( Arenaria interpres), Red Knot ( Calidris canutus), and Sanderling ( Calidris alba) foraged significantly more on sand and gravel compared to pools and swash zone, Semipalmated Sandpiper ( Calidris pusilla) foraged significantly more on sand and gravel compared to swash zone, but not significantly more compared to pools, while differences in use of microhabitats by Dunlin ( Calidris alpina), and Short-billed Dowitcher ( Limnodromus griseus) were non-significant. Turnstones used digging and turning stones, and pecking significantly more than probing, Semipalmated Sandpipers used pecking significantly more than probing, while all other species used probing significantly more than pecking. Knots and Sanderlings had the highest level of overlap both in use of microhabitats and foraging techniques, while turnstones and dowitchers had the lowest. Ruddy Turnstones were the only birds that used digging and turning stones to obtain food and these two foraging methods seemed to be the most important variables discriminating turnstones from other co-occurring shorebirds. However, despite the slight differences in use of foraging methods and microhabitats by different species, this study documented weak partitioning among shorebirds, particularly between sandpipers and dowitchers. These results indicate that the short-term absence of clear niche partitioning on a local scale may occur in shorebird communities.