Prey switching in red-necked phalaropes Phalaropus lobatus: Feeding limitations, the functional response and water management at Mono Lake, California, USA

Abstract

The ability of red-necked phalaropes Phalaropus lobatus to switch prey under conditions of changing prey abundance at Mono Lake, California, was tested in order to predict the potential effects of continued water diversions there on migratory waterbird populations. Red-necked phaloropes cannot switch prey because they are incapable of surviving on a diet of just the hardier of two invertebrates threatened by salinity increases at Mono Lake. Individuals experimentally limited to brine shrimp Artemia monica as a primary prey source lost mass rapidly until death ensued, or until they were offered other prey. These data show that a marked preference for one prey may indicate important physiological limitations in a predator. Such limitations may partly explain Murdoch's empirically supported prediction ( Ecol. Mongr. (196), 39, 335-54) that prey switching will not occur where strong prey preferences exist. These results also indicate that strong prey preferences of migratory birds can, and probably should, help determine water management policy at wetlands of importance to shorebirds, especially in cases where initial prey diversity is low.