Black-crowned Night-Heron at Ding Darling National Wildlife Refuge in Florida, one of the many places that this bird winters.
Black-crowned Night-Heron up close at Lake Calumet wetlands.
Black-crowned Night-Heron Rookery on 122nd Street
The state-endangered Black-crowned Night Heron depends heavily on wetlands in the Calumet region for its continued survival in the states of Illinois and Indiana. Almost exclusively a colonial nester, there is little doubt that the Calumet nesting colony at this time represents the largest breeding population of this species in the state of Illinois.
Only five other nesting colonies (totalling from 1 - 113 nests each) were located in Illinois in 1996. The species has essentially been extirpated as a breeding species from the state of Indiana since 1980, but small numbers (circa 10 nests) have begun to breed again in northwest Indiana during the last few years.
The following is a brief history of the Calumet colony taken from the "Conceptual Plan for the Lake Calumet Ecological Park: Chicago, Illinois" by James E. Landing (August, 1986, p. 35):
"Through most of the 20th century for which records are available the heron rookery was located along the Calumet River just north of the confluence with the Grand Calumet. The construction of O'Brien Lock and Dam so degraded the area that they relocated in the Big Marsh in a small stand of cottonwoods in the central portion. Drainage of the Big Marsh illegally by Waste Management in the fall of 1981 resulted in the complete drying of the site through the summer of 1982. But even prior to this, high water levels covered the nesting site in 1981 and the birds could not be located. In the spring of 1982, they were rediscovered in a cottonwood grove just west of the O'Brien Lock and Dam, where they concentrated in 1983 and 1984. In 1985, with the return of normal water levels in the Big Marsh most of the birds returned. A Corps of Engineers study in 1985 revealed 492 nests in the Big Marsh and 139 at Whitford's Pond. In 1986 only 417 nests were found: all in the Big Marsh, none at Whitford. This was a decrease of 34% occasioned by higher water levels and less vegetative surface through muskrat activity. The continued presence of the colony at Lake Calumet depends on the maintenance of a stable site with proper water controls."
Black-crowned Night Herons are most active at dawn and dusk, but they also forage in the dead of night (hence "Night-Heron") and occasionally during the day, although much of the daytime hours are usually spent loafing. While they nest in wetlands in the immediate vicinity of Lake Calumet, they routinely fly as far as 20 miles to obtain food and regularly forage in wetlands along the Grand & Little Calumet Rivers in NW Indiana, and as far west as the Palos area in SW Cook County. Thus, it is important that all of these wetlands be preserved to assure the Night Herons continued survival.
Black-crowned Night Herons eat fish, frogs, tadpoles, crayfish, snakes, mice, and young birds, and thus are relatively high on the food chain. Like other fish-eating birds (cormorants, herons, egrets) and predatory birds (Bald Eagle, Osprey, Peregrine Falcon), Night-Herons have probably benefitted from the ban on DDT use in 1972. DDT accumulates in the body tissues of fish eating and predatory birds, causing eggshell thinning. Black-crowned Night-Herons, however, do not seem to have "bounced back" in as big a way as some of these other species have in recent years, so perhaps other mechanisms are at work. Black-crowns are fairly small herons, and perhaps they are routinely "pushed out" of communal nesting colonies by the larger and more aggressive species of herons and cormorants.
Black-crowned Night Herons often begin nesting around mid-April, and generally all young have fledged by about the end of July. Then begins a period of "post-breeding dispersal," where young and old birds alike disperse across the midwest to exploit wetlands in other areas for food before heading south for the winter. Many of these birds leave the Calumet area at this time. Black-crowned Night Herons are sensitive to disturbance and should not be approached too closely when nesting. Besides the destruction of foraging and nesting habitat, the Illinois Endangered Species Protection Board lists harrassment and encroachment by humans a major threat to the survival of this species. A good rule of thumb is to remain at least a city block away and observe the birds with binoculars or a spotting scope."