This spring, a changing environment for Rock Creek Park’s songbirds
By Sophie Kahler and Zoe Swiss
On a warm and sunny day in early March, you might be able to spot a few birds perched in the budding trees of Rock Creek Park — and if you listen closely, you can hear them.
Though it’s early in the season for the area’s songbirds, the chirps and calls of some species are a sign of what’s to come as temperatures warm and flowers bloom. But this spring highlights a challenging trend: fewer songbirds are returning to the park each year.
Rock Creek Park has long been a hotspot for birders to watch the migration of northbound songbirds each spring. Positioned along the Atlantic flyway migration route, D.C.’s largest park is home to a variety of birds passing through each year on their return from the winter retreat to warmer climates.
“A key part of the park’s value is as a safe migration route for birds that are traveling north and south,” said Bill Yeaman, the National Park Service’s Resource Management Specialist for Rock Creek Park.
To the casual park goer, Rock Creek Park seems inundated with birds each spring. But changing migration patterns and habitat disruption mean that songbirds are disappearing from the area, leaving conservationists concerned about the future of the park’s biodiversity.
The vanishing songbird
Over 150 species of birds call the 1,754-acre Rock Creek Park home. Many of those species are migratory birds that inhabit the park during the warmer months and migrate south to Central and South America for the winter. But each year, fewer birds are making the thousand-mile journey. A 2019 study revealed that the bird population of North America plummeted by almost a third since 1970, resulting in a net loss of nearly three billion birds.
One species falling victim to this trend is the wood thrush, a small, cinnamon-brown songbird with striking black spots — the official bird of D.C. The wood thrush population in the United States has decreased by more than 60% since 1966.
Yeaman has noticed this decline in Rock Creek Park.
“Wood thrush, which is a bird that likes to nest in the interior, as well as scarlet tanagers, red-eyed vireos, ovenbirds — these are interior birds whose numbers have dramatically gone down,” he said.
That loss has been traced primarily to the destruction of the birds’ North American habitat, where they spend roughly half the year from April to October in eastern deciduous forests. But their winter habitats in tropical forests from Mexico to Colombia are changing as well.
“The habitat in general for that kind of environment is shrinking throughout the country and certainly in Central America… It’s a loss of habitat on both ends of their journey,” Yeaman said.
Songbirds prefer dense, lush forests to breed in, and the loss of viable forested areas within the park has several causes. Urban development has disrupted much of D.C.‘s once-forested areas, including the Piney Branch stream valley in the southeastern section of Rock Creek Park. After the tributary was paved over to create Piney Branch Parkway in the 1930s, trees that grew along the banks disappeared, reducing the songbird habitat.
Human recreation within the park erodes the habitat as well.
“Our biggest problem is what we call social or unauthorized trails, which have been created over time with more and more people in the park,” Yeaman said. “It disturbs habitats, it compromises the integrity of the forest, and each trail has its own side effects in terms of protecting sensitive habitats.”
He notes that canine park visitors are a concern as well, as unleashed dogs wander through the woods and disturb the conditions off-trail.
Vulnerable habitats exacerbate competition between species, and in Rock Creek Park, a large deer population poses an issue for songbirds. In recent years, the park’s white-tailed deer population hit almost 100 deer per square mile — five times the National Park Service’s goal — which means that deer are overgrazing on trees like maples and hemlocks where songbirds live and feast on insects.
But while plants are dwindling in some places, they are taking over in others. Invasive, or non-native, plant species such as bush honeysuckle, English ivy, and bamboo disturb the ecosystem by reducing birds’ native food sources and depleting the fertility of the soil.
“Native plants are greatly compromised by invasives,” explained Yeaman. “Without that [native] food source, you’re affecting the food chain at the insect level, which is the basis for everything above them, including songbirds.”
When springtime comes too soon
New research suggests that ‘early spring’ may be affecting migration patterns as well — that’s the recent phenomenon of warm weather arriving earlier in the year, causing premature blooming and shifting the migration timeline.
Migratory songbirds travel with the weather — if winter lasts longer, they’ll stay down south; if spring arrives early, they’ll head north with it. And as climate change accelerates, spring temperatures are beginning earlier each year. Some regions of the U.S. are experiencing springtime weather an average of six to 18 days earlier than usual.
That means birds are shifting their migration patterns. Songbirds with shorter migration routes like the pine warbler and American robin are picking up on signs of the changing seasons and migrating northward earlier, but species with longer routes from Central and South America are falling behind.
Male birds are seemingly adapting to these changes better, returning to breeding grounds an average of one week before females. These gaps could pose reproductive challenges for birds and cause them to be out of sync with their fledglings’ food supply.
Conservationists in Rock Creek Park are worried about how songbirds will weather the changes.
“Those fresh leaves that come out in the spring are very tender and don’t have as many toxins — they’re very tasty for insects,” said Steve Dryden, a local conservationist and who has been involved with the D.C. Audubon Society and Rock Creek Conservancy.
“If leaves start blooming earlier, and the insects start eating them earlier, that whole cycle gets thrown off and it might be bad for the reproduction of the birds. The birds are used to coming at a certain time in the spring. They may be too late.”
Scientists are still tracking these seasonal shifts, which are changing with the effects of climate change. In the meantime, experts are focusing on habitat preservation and restoration to ensure songbirds have a place to return to each year.
Preservation and protection
Environmental groups in the D.C. area are working to protect and cultivate the forests of Rock Creek Park that are still viable songbird habitats.
When Dryden learned about the plight of the wood thrush in 2013, he launched an initiative to help restore songbird habitats in the park. Today, Rock Creek Songbirds has raised over $150,000 and planted more than 600 native trees in Rock Creek Parks’s Piney Branch.
Working with local schools and community groups, Dryden has become a steward of Piney Branch by creating lush habitats that support not only songbirds, but all biodiversity in the park. Dryden and volunteers with Rock Creek Songbirds remove invasive plants, clean up litter, plant new trees, and monitor the restoration projects.
The Rock Creek Conservancy is protecting bird habitats by developing mini-oases throughout the park to remove invasive species from one small area at a time. They regularly host cleanup events and train a group of volunteers known as Weed Warriors to tackle these invasive species sites.
“Our goal is to reduce invasive cover to less than 5%, to reduce the stress on the trees and to hopefully let the forest recover,” said the Conservancy’s Executive Director Jeanne Braha.
And the National Park Service is doing its part to preserve songbird habitats in Rock Creek Park by regulating human recreation and educating visitors about best practices. They even organize people to engage in community science efforts like the Audubon Christmas Bird Count. Each Christmas, Yeaman ventures into the park early in the morning with volunteers to count and track all the birds they see that day. The 123-year-old tradition helps conservationists and researchers understand current bird populations.
Bringing it home
According to Yeaman, people can help protect songbirds from their own backyards by planting native shrubs and trees. If you’ve got a windowsill, you can plant native wildflowers.
“People can do these things on their property to help. It would improve just the general condition of the environment, including songbirds habitats.”
And of course, the Rock Creek Songbirds, Rock Creek Conservancy, and the National Park Service are always in need of volunteers to help bring the music of songbirds back to the park.
As D.C. enters springtime, the songbirds will flock to Rock Creek Park, nesting among the trees after a long journey north. They will continue to do so, year after year, as long as we make sure they have a safe place to fly home to.