Species Profile
In Pennsylvania, the Green heron is listed as a low concern species.
The black-crowned night-heron (Nycticorax nycticorax) was once considered a fairly common nesting heron in Pennsylvania. In fact, B. H. Warren (1888) claimed it was the most common nesting heron in the state second only to the green heron (Butorides virescens). Black-crowned night-herons have always been more common in the southeastern counties than in other parts of the state, mainly along the Susquehanna and Delaware River corridors, but the species is now difficult to find anywhere else in the state. The number and size of colonies have declined in recent years, especially in the northern and western counties (Luzerne and Crawford, for example) where the species no longer nests.
The Pennsylvania Game Commission and agency partners count active nests at known nest sites every year to monitor population trends. In recent decades, black-crowned night-herons were found nesting at locations in Dauphin, Lancaster, York, and Berks counties. Wade Island, Dauphin County, has been surveyed annually since 1985. This colony had the largest number of black-crowned night-heron nests for many years. It reached its peak in 1990 with 345 nesting pairs but has declined since then, primarily because of competition from double-crested cormorants that began nesting on the island in 1996. On Wade Island, the 5-year average night-heron count from 2005 to 2009 was 83 nests; from 2010 to 2014 it was 60 nests. During that time a smaller colony on hospital grounds in Lancaster County grew to be the largest, reaching 83 nests in 2012; since then it has declined as well. The geographic range of the back-crowned night-heron nesting population has changed dramatically from a much wider distribution to these few diminishing colonies on which we keep a close watch.
This small, chunky crow-sized heron is found around ponds and lake edges, along wooded streams and rivers and in marshes and swampy thickets. Its length is 16 to 18 inches, its wingspread 25 inches. The bluish-green back and wings give the bird its name; underparts are dark, while the neck and head are reddish-brown, and the crown is black. This bird may appear all dark from a distance, especially on a cloudy day. Immatures resemble American bitterns although green herons are smaller with a much shorter wingspan. For a while, this species was combined with the striated heron (Butorides striata) and the combination was called the “green-backed heron.”
A green heron flies with deep wingbeats. Its call is a sharp, descending skeow, sometimes given in flight. The green heron feeds on small fish, frogs, insects, worms, lizards and salamanders, hunting early in the morning and late in the afternoon. Herons employ some 36 feeding behaviors and the green heron is one of the few birds to use tools among its hunting techniques. While foraging, it may lure prey in by dropping a twig, feather, worm, insect or other bait onto the surface of the water. It then waits motionless, with head and neck retracted and ready to strike, until fish or other prey comes to the bait. This heron also slowly stalks shallow water and stream banks; nudges prey into a more favorable position with its feet; waits perfectly still in ambush; and dives into water from an overhanging perch.
Green herons usually nest in shrubs or trees overhanging the water, but sometimes in orchards and groves away from any water source. A pair may nest by itself or in a loose colony of other herons (the green is not as gregarious as the great blue). The nest is a platform of twigs and sticks lined with finer material. Some nests are so shallow and flimsy that the eggs can be seen through the bottom. The male selects the nesting site and starts building, and the female finishes the task. Outside nest diameter is 10 to 12 inches. Four to six oval, pale blue or green unmarked eggs are laid, which both sexes incubate for 19 to 21 days. Pairs typically raise one brood.
Nesting colonies are protected through the Pennsylvania Natural Heritage Program and the Environmental Review process. Colonies are monitored through the PGC's colonial waterbird program. The largest colonies are part of the Sheets Island Archipelago and Kiwanis Lake Important Bird Areas. More studies of the ecology and behavior of this species in Pennsylvania are needed to better understand its conservation needs.
