Introduction

The Black-crowned Night-Heron is a cosmopolitan species, breeding on every continent except Australia and Antarctica. Although widespread and common in North America, its nocturnal and crepuscular feeding habits render it less obvious than diurnal herons outside the breeding season. This heron feeds on a wide variety of freshwater and marine organisms, especially on fish. Declines in many of its populations noted in the late 1960s were probably attributable to the use of DDT, a persistent pesticide. Because these birds are high on the food chain, accumulate contaminants, and have a wide geographic distribution, they serve as indicators of environmental quality. In the past, they were shot and trapped as pests at fish hatcheries, but have also been hunted for food.

Black-crowned Night-Herons are colonial breeders and gregarious throughout the year, often associating with other species of herons. They are flexible in their selection of breeding colony sites, but often nest on islands or in swamps, suggesting they gain some protection from predators in doing so. The tendency for their young to disgorge their latest meal when disturbed has made this species a favorite for feeding studies. For naturalists who enjoy the shore and marsh, this heron’s distinctive call is a quintessential sound of dusk and night. As A. C. Bent (1926) reported enthusiastically, “How often, in the gathering dusk of evening, have we heard its loud, choking squawk and, looking up, have seen its stocky form, dimly outlined against the gray sky and propelled by steady wing beats, as it wings its way high in the air towards its evening feeding place in some distant pond or marsh!”