Regional Patterns of Wading Bird Productivity in Northeastern U.S. Estuaries

Abstract

-We investigated wading bird productivity in four estuaries from Delaware Bay to Boston Harbor in northeastern U.S.A. over the period 1986-1998. To document and characterize reproductive performance of numerically dominant species for use in wildlife and habitat management planning, we recorded 1) number of eggs laid, 2) percent of eggs hatched, 3) percent of hatchlings surviving 10-15 days post-hatch, 4) number of nestlings produced, and 5) factors of offspring mortality in nests of Black-crowned Night Heron (Nycticorax nycticorax), Snowy Egret (Egretta thula), Cattle Egret (Bubulcus ibis), and Glossy Ibis (Plegadisfalcinellus). We randomly selected 30-50 nests of each species (as available) for study at colonies in Delaware Bay (1993-1998), New York Harbor (1986-1994), Cape Cod (1990-94), and Boston Harbor (1993-94). In addition, we recorded abundance of nesting wading birds and avian predators in most years of study. Colony size ranged from 120-8,300 nests. Clutch size of all species was greater at northern-most sites. Loss of eggs varied between estuaries for all species except Glossy Ibis. Hatching success ranged from 75-88% and differed between estuaries for Black-crowned Night Heron and Glossy Ibis. Hatchling survival ranged from 16-87% and was lowest in Delaware Bay for all species. Nestling production was lowest in Delaware Bay for all species. In general, predation was high in Delaware Bay and egg inviability was high in Boston Harbor. Predation of nestlings was greatest in Delaware Bay for Cattle Egret, but there were no differences between estuaries for other species. Proportions of avian predators to nesting herons did not explain high predation rates in Delaware Bay. Received 18 April 2001, accepted 21June 2001.