Black-crowned Night-Heronsof the Lake Calumet Region,Chicago, Illinois

Population trends in a Black-crowned Night-Heron colony at Lake Calumet Wetlands

Abstract

The number of active black-crowned night-heron (Nycticorax nycticorax) nesting colonies in Illinois has declined significantly over the past century. Habitat loss/degradation and other factors such as exposure to environmental contaminants and competition for nest sites at established colonies may have contributed to this decline. In this study, we examined recent trends in population levels of Black-crowned Night-Herons nesting at wetlands associated with Lake Calumet in southeastern Chicago, Illinois. The number of black-crowned night herons nesting annually at these wetlands has fluctuated widely over the last two decades. Immigration of herons from riverine colonies may have driven population increases during the mid-1980s and early 1990s. However, this population has remained relatively stable at between 300 and 400 pairs during 1997–2003.