SPECIES INTERACTIONS IN A MIXED COLONY OF COMMON TERNS (STERNA-HIRUNDO) AND BLACK SKIMMERS (RYNCHOPS-NIGER)

Black skimmers (R. niger) frequently nest among common terns (S. hirundo) on coastal islands from North Carolina to New York [USA]. Behavioral interactions among terns, skimmers and several potential avian predator species were quantified during the 1973 breeding season at Fisherman Island, Virginia [USA]. Common terns were dominant to skimmers, chasing and dive-attacking neighboring pairs, while skimmers rarely chased terns. Despite agonistic interactions, nesting success of both species was no different whether nearest neighbors were conspecifics or heterospecifics. Common terns chased away potential avian predators much more frequently than did skimmers. Black skimmers appear to derive a protective cover benefit from nesting among the terns. Neither nest-site limitation nor food information-sharing appear to account for the species associations.