Wilson's Phalaropes Can Double Their Feeding Rate by Associating with Chilean Flamingos

Abstract

Birds often participate in mixed-species foraging associations to improve their feeding efficiency. Wilson's Phalaropes Steganopus tricolor wintering in saline lakes of the Atacama Desert, northern Chile, were found to feed either solitarily or in close proximity (commensally) to Chilean Flamingos Phoenicopterus chilensis. Those individuals following Chilean Flamingos were picking up prey (mainly copepods) stirred up by flamingos rapidly stomping their feet (‘foot paddling’). In contrast, Wilson's Phalaropes ignored Andean Flamingos Phoenicoparrus andinus and Chilean Flamingos using different foraging tactics. Feeding rates of Wilson's Phalaropes associating with Chilean Flamingos (38 ± 9 prey/min) were significantly higher than those of solitary phalaropes (17 ± 6 prey/min), indicating that this association allows profitable feeding on small prey suspended in water. Although this association appears to involve a high benefit to Wilson's Phalaropes and a low cost (if any) to Chilean Flamingos, thus partly explaining the stability of mixed-species groups, it is restricted to moderate and deep foraging depths. Three other shorebird species (Baird's Sandpiper Calidris bairdii, Lesser Yellowlegs Tringa flavipes and Greater Yellowlegs Tringa melanoleuca) associated with the Chilean Flamingo at shallower foraging depths, indicating these facilitative interactions are species and context dependent.