RUBEGA, M.A. *; RAY, M.K. *; University of Connecticut: Surface tension transport in red phalaropes Phalaropus fulicarius; an examination of interspecific variation in a common feeding mechanism.

Surface tension transport (STT), an avian feeding mechanism which uses the surface tension of the water adhering to prey to transport it along a bird’s beak and into the mouth, was first documented in red-necked phalaropes (P. lobatus), and subsequently in Wilson’s phalaropes (P. tricolor). To date STT has been measured in a total of 5 species of shorebirds, which span a range of beak sizes and shapes. As part of a research program on the evolution of feeding mechanics in birds, we investigated the use and kinematics of STT in red phalaropes (P. fulicarius). Red phalarope beak morphology is quite different from that of other phalaropes and in a way that might be expected to eliminate or reduce their ability to perform STT. Red phalaropes use STT; they spread their jaws more widely during a cycle of STT, resulting in the drop moving farther, but without a significant increase in drop speed, compared to other species eating insect larvae. Wilson’s and red phalaropes display comparable drop speeds even when transporting prey with about a six-fold difference in mass. Given that STT is employed by closely related species with different beak shapes, it provides an exciting opportunity to examine how feeding performance changes with changing beak shape, and thus how beak shape evolves. Data from red phalaropes provides insight into the potential costs and benefits of a dorso-ventrally-flattened beak, in a group of birds in which flat beaks are rare.