The Status and Distribution of the Black-Crowned Night Heron in Wisconsin

Abstract

In January 1978 a 2-year study was initiated to determine the status and distribution of the black-crowned night heron (Nycticorax nycticorax) in Wisconsin. During the spring and summer of 1978 and 1979, 68 areas were searched for colonies. At least 13 colonies, ranging in size from 2 to 702 pairs, were active during the study. Colony size varied up to 244% between years. The productivity of 2 Wisconsin black-crowned night heron colonies differed significantly between years but not between colonies. The average number of fledged young per nesting pair at these 2 colonies was 1.46 and 2.36 in 1978 and 1979, respectively. The 2 year total, 1.98, was considered sufficient to maintain the current population level. Black-crowned night herons were closely associated with large, type-4 wetlands, especially those in which the amounts of cover and open water were approximately equal and interspersed. They preferred to nest in deciduous trees and shrubs growing in standing water or located on islands or peninsulas.