After bushwhacking two miles through the tidal hardwood-swamp forest along Potomac Creek in Stafford County, Va., we could finally hear them. It was a cacophony of squawks and gurgles — the sound of hundreds of hungry birds in one of the largest great blue heron rookeries in the Chesapeake Bay watershed.
More than 250 enormous nests were counted by monitors this year at the Potomac Creek Heronry. The nests are made of big sticks and other woody material, are up to four feet wide and three feet deep, and are perched in the canopy 80 to 100 feet high. But nesting high in the trees leaves chicks susceptible to bald eagles and bad weather. Unfortunately, there have been wind events that have blown over trees, destroyed nests and killed birds.
We tip-toed around so as not to disturb the skittish birds. Peering through binoculars, I could see the fledglings with their long necks and pointy beaks craned skyward, cackling for their next regurgitated morsel.
Along on the tour to the heronry that day was Kathy Baker, the assistant director of the Stafford County Department of Planning and Zoning. She wrote her master’s thesis on the colony and has been monitoring the birds for years.
Baker recalls the 2012 derecho vividly. It blasted through the area producing an 80-mph wind gust at Fredericksburg, just a few miles to the south of the heronry. According to Baker, more than 140 nests were lost in the storm — from 296 before the derecho to 153 after. The only saving grace was that the storm may have been late enough in the season to not affect the birds; herons typically leave their colonies by late June.
But that wasn’t the case in 2008 when severe weather occurred before the birds took flight from their nests.
“There were several weather events during the 2008 breeding season, including an EF-2 tornado on May 8, and what was likely a micro-burst on June 4,” Baker said. Four thunderstorms with at least 50-mph winds occurred near the heronry between March and June. “The nest count in January 2008 indicated 358 nests, and in January 2009, there were 272 nests,” Baker recalled.
“Some trees were completely downed, including one tree that had contained 13 nests the previous year,” Baker said. “There were several bird carcasses on the ground, so it is possible that some of the birds were killed during these events.”
Herons are resilient, though, and by 2010, the number of nests was back up to 346.
Protection of the Potomac Creek Heronry from human development occurred in the late 1990s. Because of the destruction of wetlands from the construction of Stafford Regional Airport, county officials set aside 70 acres of the upper Potomac Creek (and the heronry) for permanent protection. In 1999, the Northern Virginia Conservation Trust had the opportunity to take stewardship of the land and the duty of preserving it for perpetuity.
The situation is pretty good for the Potomac Creek Heronry and Great Blue Herons in general. The population on Potomac Creek is stable. A 2013 study found that the herons have made a “dramatic comeback since their population low in the 1960s.” The survey concluded that no other waterbird is as abundant in the Chesapeake Bay.