SAND-COLORED NIGHTHAWKS PARASITIZE THE ANTIPREDATOR BEHAVIOR OF 3 NESTING BIRD SPECIES

On beaches along the Manu River of southeastern Peru, four bird species (Black Skimmer, Rynchops niger; Large-billed Tem, Phaetusa simplex; Yellow-billed Tern, Sterna superciliaris; Sand-colored Nighthawk, Chordeiles rupestris) nest in mixed-species associations. Costs and benefits of the association were distributed asymmetrically among the species. Nighthawks never actively defended their nests against predators. Terns and skimmers defended their nests by aggressively mobbing predators, and indirectly defended nearby or adjacent nests of nighthawks. As a result, nighthawks had greater hatching success when nesting near terns and skimmers. Terns and skimmers spent more time engaged in antipredator behaviors and being vigilant, but less time in parental care, and experienced lowered hatching success when among large nighthawk groups. In addition, both tern species fledged significantly fewer young per successful nest when nesting with many nighthawks. Results of this study demonstrate the first known parasitic relationship among members of a mixed-species nesting group.