by Steve Dryden
Though Rock Creek National Park contains large tracts of wooded areas, overall, the tree canopy and layers of understory have been shrinking in recent years. A new initiative, Rock Creek Songbirds, is restoring habitat in the park and adjacent neighborhoods for the wide range of resident and migratory songbirds, including the wood thrush – the District of Columbia’s official bird.
The reasons for the decline of wooded habitat are numerous. Deer browse has for all purposes halted the regeneration of oaks, which are the most important trees for attracting a diverse set of insects that are crucial bird food. Exotic, invasive species such as English ivy and porcelainberry, which are much less attractive to native insects, are smothering trees and blanketing the ground, cutting off another source of plant and food source diversity.
Extreme weather has toppled numerous old trees in the Forest Hills DC area as well as in park stream valleys, while the proliferation of “social trails” unauthorized by the Park Service continues to disturb bird nesting and feeding areas. To make matters worse, new projects such as the rehabilitation of the Soapstone valley sewer system will add to the disruption of the habitat.
Songbird population nothing to sing about
Loss of habitat has been linked to the dramatic decline in wood thrush populations throughout its migratory range, which stretches from Canada to Central America. The wood thrush prefers deep woods for its nesting activities here, and its feeding habits can be upset by the presence of off-leash dogs. (Park Service regulations call for dogs to be under the control of an owner at all times.)
Wood thrush numbers in the Washington metro region have dropped sharply in the past half century, according to studies carried out by the U.S. Patuxent Wildlife Research Center in Laurel, Maryland. Since 1966, when the center began its North American Breeding Bird Survey, wood thrush numbers have declined between two and three percent annually in Virginia and Maryland.
The center’s studies do not target the District, and the reason is telling: bird counters do their work by car and need to be able to stop along the shoulders of rural or semi-rural roads to listen for bird calls.
“There’s no habitat left along roadsides,” or shoulders, for that matter, in Washington for the surveyors to use, said David Ziolkowski Jr., program ornithologist at the Patuxent center.
And, on a larger scale, the fragmentation of Eastern U.S. forests caused by suburban sprawl has boosted the number of parasitic cowbirds, which don’t require dense tree cover and will lay eggs in wood thrush nests. The wood thrush mistakenly protects those eggs and feeds the cowbird young – who are larger and more aggressive, frequently starving the wood thrush hatchlings.
Greg Butcher, one of the federal government’s top migratory bird experts, surveyed an area of Rock Creek Park near Peirce Mill four years ago to count the pairs of breeding wood thrush. He was surprised to find only a handful.
“Among all the migrants, the plight of the Wood Thrush is particularly worrisome,” Greg says. “The population is declining at a rate in North America that brings the population down to nine million individuals, about 30 percent of what it was 40 years ago.”
“Songbird” is a generic term that refers to a group of birds in which the vocal organ typically is developed in such a way as to produce a diverse and elaborate song. Numerous species of songbirds, originating in Latin America, either nest in or pass through the District of Columbia each spring. This group of migrants includes many warbler species, flycatchers, thrushes, orioles, and strikingly-colored birds such as the Scarlet Tanager and Indigo Bunting.
Year-round residents of our area such as American robins, northern cardinals, and chickadees are also classified as songbirds, and of course most birds (and wildlife) benefit from habitat restoration.
The Songbirds initiative, focused on the Piney Branch stream valley adjacent to Mt. Pleasant, receives major funding from Toyota TogetherGreen, a conservation program of the National Audubon Society and Toyota. A volunteer tree planting event with Casey Trees kicked off the initiative in late November 2013. The National Park Service also put in several dozen trees. By this fall, about 200 trees and shrubs will have been planted or protected from deer predation. Species planted included oaks, tulip poplars, serviceberry, dogwood, viburnum, eastern red cedar, and American holly.
How you can help
The most important thing individuals can do is to plant oaks (if you have a yard that is large enough), no matter where in the city you live. As oaks take decades to reach maturity and produce large numbers of acorns, and can live 200 to 300 years, you’ll be passing on a great legacy.
Plus, keep cats indoors and dogs leashed in the park.
Volunteers are needed to help clear invasive vines and other exotic plants this fall. Contributions can be made to the Songbirds tree fund. Schools can assist by planting trees and protecting oaks on their properties. Classroom presentations are made upon request to the project director, Steve Dryden. He can be reached at (301)512-5899, or email@example.com. The project website is audubondc.org/rock-creek-songbirds.