Utility of the curved bill of the CurlewNumenius arquataas a foraging tool

Abstract

We set out to test the proposition3 that curlews' bills are decurved to allow them to follow a complex 3-dimensional search path when feeding. This was done using wooden models of male and female bills, both with and without normal curvature. These were inserted into crab burrows in saltmarsh creeks and into gaps under rocks on the shore. Curved bills penetrated further than straight ones into both types of cavity. Curved bills were also capable of greater rotation at maximum penetration. This suggests that Curlews can reach more crabs by having curved bills, and having reached them, can grasp them more effectively. Female bills penetrated further than male ones, but male bills rotated more at equivalent penetration distances. Thus, although a short bill cannot penetrate as far, it is probably more efficient at extracting food items from smaller cavities.