Twenty-six bundled-up nature enthusiasts gathered in the morning fog and 30-degree chill by the frozen Potomac River recently and trudged through a soggy forest floor, with necks stretched skyward and big chunks of yellow chalk in hand. The pursuit? The nests of Ardea herodias, the Great Blue herons of the Mason Neck National Wildlife Refuge.
Established in 1969, the refuge has one of the largest heron rookeries in the mid-Atlantic region. Herons are colonial birds — they lay and incubate eggs and raise their young in colonies of nests close together in the tops of trees 30 to 70 feet above ground.
Nest counters that Saturday found 1,320 nests in the trees, down slightly from the 2002 total of 1,378. Refuge managers have been keeping records for almost 20 years. Joe Witt, refuge biologist, said that the number of nests tripled in the 1990s, growing from a little over 500 in 1988 to 1,500 in 1998. "For many reasons, the population wobbles," he said. "The numbers do not go up in a straight line. No species population except humans goes up and stays up," he added.
The nest hunters divided into five teams, formed a line and walked slowly across the forest. Counters on each team stopped at any tree that had a nest, counted, called out the number to the team's recorder and marked the tree with yellow chalk to indicate that the nests had been counted. This method prevented duplication and misses. Most trees had more than one nest; the record-setter that Saturday was 27 nests in one tree — "high density," land-use planners would say. In a little over an hour, my team of two counters and one recorder counted 259 nests in 76 trees and 42 nests on the ground, probably casualties of a storm.
Charlie Creighton, a Mason Neck resident, has organized the count for six years. "I enjoy the beauty of the area and the opportunity to contribute to the conservation and scientific work of the U.S. Fish and Wildlife Service," he commented. "This is why many of the participants return year after year."
VOLUNTEERS INCLUDED first-timers Michelle DeStafano; her husband, Alan Janusziewicz; and daughters Hannah, 11, and Audrey, 14, of Prince William County. "We decided it was a nice way to get outside and do something and learn about nature," she explained. "There're a zillion nests. I had no idea there were so many. It was mind-boggling. We want to do it again."
A rookery is a breeding ground for gregarious birds. For Great Blue herons, it is also called a “heronry.” With much Atlantic coastal habitat lost, a rookery in a heavily developed area like Northern Virginia is a rarity and a treasure.
Great Blue herons are tall, bluish-gray wading birds standing around 46 inches. They have a dagger-like bill, white crown, black eye-stripe, black head plume down the back of the neck, shaggy white breast feathers and dark legs. In the shallows of the Potomac and in area wetlands, one can see them stalking for food. They often stand motionless, then suddenly and swiftly spear an unsuspecting fish or frog. At times, you can even see the victim squiggling down the narrow, long neck of the heron en route to the bird's viscera.
HERON NESTS are made of loosely-woven sticks and look almost accidental, some so meager that one has to wonder how these scraggly patches of sticks could hold the three to five eggs the herons lay. Truly modern birds, both the male and female build the nest, starting in March. Male and female both incubate the eggs for 28 days and both sexes feed the young, who leave the nest or fledge after about 60 days. By June, the rookery is silent once again, and the forest floor is littered with fish bones, feathers and white bird droppings.
As bald eagles soared overhead and Canada geese honked their arrival, the heron enthusiasts left the rookery, imagining the treetops soon full of big, blue-gray birds nestled on their future progeny.