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More herons call area waterways home

Great blue herons can be found stalking fish along any tidal creek or river in the Fredericksburg area, and most of the Chesapeake Bay.

A newly released survey of the majestic, slate-blue birds says that’s because the number of breeding colonies has grown dramatically since the early 1960s when the pesticide DDT decimated populations throughout the estuary.

And it appears that a corresponding boom in bald eagle numbers, and other factors, may be changing herons’ nesting habits, the researchers say.

Herons gather in nesting colonies. But those colonies have been shrinking as the birds break up into smaller groups.

“That’s gotten much more obvious in the last decade or so,” said Bryan Watts, director of the Center for Conservation Biology, based at the College of William and Mary in Williamsburg.

The average heron colony size this year was 35 pairs, compared to more than 110 pairs in 1985.

During May and June, Watts and Bart Paxton, a center research biologist, logged 200 hours in the air, surveying heron nesting sites along 900 miles of the bay and its tributaries.

The reasons for smaller breeding colonies are not fully understood.

Herons and eagles, Watts says, prefer the same types of nesting areas: old trees adjacent to feeding sites, “so there’s an overlap.”

“We have something like 60 or 70 eagles’ nests in [heron] colonies in Virginia now. Historically, we didn’t have that,” Watts said.

With the proximity, some eagles prey on their heron neighbors. A photograph posted with the survey on the center’s website shows two eagle chicks in a nest strewn with heron feathers.

Another reason breeding herons are spreading out could be because they’ve worn out longtime venues, or that prime real estate is getting harder to find.

“Whether that’s due to herons damaging the trees” and moving to new areas “or the eagles moving in, it’s not clear,” Watts said.

Food could be a factor.

“Great blues forage about 15 kilometers out from a colony, and they begin to saturate” available feeding areas.

Watts estimates the bay heron population puts away about 8,200 metric tons of fish a year. A metric ton is 2,205 pounds.

In the 1960s, only about a dozen heron breeding colonies were left bay-wide. DDT insecticide thinned egg shells, resulting in fewer chicks. It was banned in 1972.

This year’s survey found 14,126 pairs within 407 breeding colonies, making great blue herons the most widespread and abundant breeding bird on the estuary.

Great egrets, sometimes called great white herons, were also counted. Egrets historically have stuck close to the coast, but have been moving farther inland as their numbers increase, Watts says.

The survey recorded 1,775 egret pairs in 39 colonies—a three-fold increase over three decades.

Locally, during the spring runs of herring and shad, great blue herons gather by the dozen to feast along the Rappahannock falls above Fredericksburg. The birds hang around much of the year, catching fish and other prey.

About 500 heron pairs gather at a decades-old colony along Potomac Creek in Stafford County. The Northern Virginia Conservation Trust owns the 70-acre tract adjacent to Crow’s Nest Natural Area Preserve.

The number of breeding pairs there has remained relatively stable.

“We’re not sure why,” Watts said.

But the number of pairs at Mason Neck State Park in Fairfax County has shrunk. It has about 1,250 pairs, down from about 1,500 a few years ago.

The largest colony, with 1,450 pairs, is on Pooles Island in the bay.

The survey found 65 heron colonies along the Rappahannock, and the Virginia side of the Potomac. Those colonies support 3,499 pairs of great blue herons and 10 pairs of great egrets.

The survey was funded by the Virginia Department of Game and Inland Fisheries, the Maryland Department of Natural Resources, and the Center for Conservation Biology, a research unit within the College of William and Mary and Virginia Commonwealth University.

The Center for Conservation Biology, ccbbirds.org

 

Rusty Dennen: 540/374-5431

rdennen@freelancestar.com

GREAT BLUE HERONS

Standing 4 feet tall, with a 6-foot wingspan, great blue herons are North America’s largest heron species. Males and females look similar—with blue-gray feathers, yellow bill and brown or green-hued legs—though males are slightly larger.

They often reuse nests and typically lay about four eggs. The statuesque birds breed throughout North and Central America, the Caribbean, and the Galapagos Islands. Some populations migrate to South America for the winter.

—Audubon Magazine

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