In 1979, clutch-size and reproductive-success data were collected on black-crowned night-herons (N. nycticorax) nesting in 3 New England and two North Carolina [USA] colonies. In 1975, similar data were collected from 1 New England and 1 North Carolina colony. Latitudinal differences in clutch initiation were not evident. Mean clutch size was larger in the New England colonies. Mean clutch size was smaller in late nests from 1 New England colony studied in both years and another New England colony studied in 1979; seasonal trends in clutch size for another colonies were not found. In 1979, nest success was greater in 2 New England colonies than in 1 North Carolina colony. Within-season differences in nest success occurred but were inconsistent among colonies. In the 4 instances where statistical comparisons could be made, larger clutches were more successful than smaller ones in 2 colonies; large and small clutches had similar success in 2 other colonies. One egg was collected from each of several nests in each colony in 1979 for organochlorine contaminant analysis, and the fate of the remaining eggs was recorded. Concentrations of DDE and PCB [polychlorinated biphenyl] did not differ with clutch size; concentrations of PCB were lower in eggs laid late in the season. Although the data suggest an effect of DDE on hatching success in the northern more contaminated colonies, the impact of environmental contaminants on overall reproductive success appears to be minimal.
Additional publication details
Clutch size reproductive success and organochlorine contaminants in Atlantic coast black-crowned night herons Nycticorax nycticorax