Steep declines of colonial wading birds in northeastern North America's largest breeding population

Urban estuaries can support thriving ecosystems despite bustling human activity, and bird populations can serve as a key indicator of environmental health. The largest breeding population of colonial nesting wading birds (herons, egrets, ibises) in the northeastern United States is in New York‐New Jersey Harbor, one of the world's largest urban centers. We use a long‐term (22‐year) complete nest census dataset, covering all breeding locations within the region, to investigate trends in wading bird populations. We found that while the number of colonized islands has remained steady, the overall population has declined by 27%, faster than average declines across North American birds. Although populations of great egret ( Ardea alba ) and snowy egret ( Egretta thula ) increased, we found that black‐crowned night heron ( Nycticorax nycticorax ) and glossy ibis ( Plegadis falcinellus ) declined by 55% and 59%, respectively, over the 22‐year period and were driving overall population declines. We also found black‐crowned night heron, historically the most abundant species, could be locally extirpated as soon as 2037. The loss of black‐crowned night heron could signal a significant ecosystem shift with cascading consequences. Immediate action and investigation by researchers, resource managers, and policy makers are needed to reverse these declines and to understand the implications for the health of this important urban estuary.