Diet of nestling Black-crowned night-herons in a mixed species colony: Implications for tern conservation

Boluses were collected from Black-crowned Night-heron (Nycticorax nycticorax) nestlings in 1992 to examine the impact of night-heron predation on a restored tern colony. Boluses (n = 101) were collected from 18 nests. Fish remains occurred in 89% of nests. sand shrimp (Crangon septemspinosa) in 50%, birds in 28%, and amphibians in 16% of nests sampled: mammalian, eel, squid, and marine invertebrate remains were also noted. Regurgitated bird remains were found in five nests and included four species, Common Terns (Sterna hirundo), Common Eiders (Somateria mollissima). Gulls (Larus sp.), and the legs of an unknown wading bird. Nestling night-herons from three nests were fed tern chicks, but 92% of tern chicks known to have been eaten were fed to nestling Black-crowned Night-herons in one nest. No tern chicks fledged in 1992 and night-herons were observed in the tern colony on multiple occasions. This Study suggests that individual night-herons will specialize on waterbird prey. The subsequent removal of a specialist night-heron predator resulted in improved tern productivity.