Breeding populations of great blue herons have made a dramatic comeback within the Chesapeake Bay according to a 2013 survey conducted by The Center for Conservation Biology. As with bald eagles and osprey, great blue heron populations suffered deep declines during the DDT era reaching a low in the late 1960s of approximately a dozen known breeding colonies. The 2013 survey documented 14,126 pairs within 407 breeding colonies making the species the most widespread and abundant breeding waterbird in the Chesapeake Bay. The population would consume an estimated 8,200 metric tons of fish annually. Colonies were documented within every county along the tidal reach of the estuary.
Map of great blue heron and great egret colonies along tidal tributaries of the Chesapeake Bay. Colonies were mapped and surveyed as part of a 2013 population assessment. Map by CCB.
An interesting finding of the survey is that the size of breeding colonies has been declining for more than a decade. The average colony size in 2013 was 35 pairs compared to more than 110 pairs in 1985. Large colonies that were stable for decades have begun to splinter and scatter across the landscape. Although the underlying cause of the decline remains unclear, one possible contributing factor may be the recovery of bald eagles. Bald eagles now nest in a growing number of heron colonies. The largest colony in the Bay on Pooles Island (1,450 pairs) now contains 4 bald eagle nests and the second largest colony on Mason Neck (1,250 pairs) now contains 2 eagle nests.
Wings of great blue heron in bald eagle nest with chicks along the Chickahominy River. Bald eagles may be altering heron colony dynamics. Photo by Bryan Watts.
In addition to great blue herons, the survey also included great egrets. More associated with coastal waters and never as common as great blue herons in the Chesapeake Bay, 1,775 egret pairs were found in 39 colonies. This number represents a nearly 3 fold increase in the population over the past 30 years.
Brood of great egrets in the lower Chesapeake Bay. Photo by Bryan Watts.
The 2013 aerial survey conducted by Bryan Watts and Bart Paxton required 200 hours of flying and covered more than 900 tidal tributaries of the Chesapeake. Funding for the survey was provided by the Virginia Department of Game & Inland Fisheries, the Maryland Department of Natural Resources, and The Center for Conservation Biology. The Center for Conservation Biology is a research unit within the College of William and Mary and the Virginia Commonwealth University.
Written by
Bryan Watts | bdwatt@wm.edu | (757) 221-2247
September 23, 2013
A bald eagle nest just off the Poropotank River in Virginia in 2003. A nest with two equal young and ample food was a normal scene during this time period. This reflects a golden period during the late 1990s and early 2000s when males had more leisure time to hunt and provide for broods. Photo by Catherine Markham.
Breeding female on the Eltham Bridge. This female was hatched on Elkins Marsh along the seaside of the Delmarva in 2010 and has held the territory on the Eltham Bridge since 2013 with three successive males. She has been very aggressive and protective of the nest site and has held the territory together. She was found with a wing injury from a collision in December and could not be rehabilitated. She is one of a number of falcons that have been documented to go down in 2022. Photo by Bryan Watts.