Scientists discover first proof of Swainson’s warbler breeding in Pennsylvania
“This is definitely a career highlight,” said David Yeany II, an avian ecologist in the Pennsylvania Natural Heritage Program at the Western Pennsylvania Conservancy,
Yeany and Nick G. Liadis, executive director of Bird Lab, made the discovery of a family group of Swainson’s warblers at the Bear Run Nature Reserve in the Laurel Highlands. The group included a male, female, and juvenile, which had hatched this year.
“It’s not every day that a state gets a new breeding bird,” Liadis said.
Yeany added that Swainson’s warblers have been documented only about 60 times in the state since they were first recorded at Bear Run in 1975 and that western Pennsylvania is at the most northern edge of its range.
The timeline of discovery
Liadis first recognized the warbler’s song at the Conservancy’s nature reserve last year while camping there with a group of people. It was along a stream, when he first heard a Louisiana waterthrush, then Liadis heard a similar but succinct song — a Swainson’s warbler. He texted Yeany as soon as he got back to an area with cell service.
“The project sort of unfolded from that one moment where I was just kind of in the right place at the right time for this very special bird and decided that it was worth studying,” he said.
They ended up capturing and banding four males of the species last summer, two at Bear Run, one each in Indiana and Blair counties. The special metal ID bands around the birds’ legs have a unique number and are with the birds throughout their lifetimes, and a color band makes it possible to identify individual birds by sight with just a pair of binoculars so the birds don’t have to be recaptured. This is helpful for the often hard-to-see Swainson’s warbler, especially because the plumage of the male and female birds is the same.
Liadis and Yeany knew the warblers they banded weren’t what are known as “overshoots,” where a warbler migrates too far north and then doubles back to a more common, southern location to breed. These birds persisted throughout the summer, though the scientists couldn’t find a nest.
Then this May, they were tipped off by a birder about a potential Swainson’s warbler at Bear Run, where they again banded a male bird. Soon after, another birder texted a photo of an unbanded male bird at the reserve.
So on July 12, Liadis and Yeany went to Bear Run to try to band that second male and to survey the habitat where warblers would likely breed. They did band another male that day, but perhaps more exciting, they spotted the male they had banded in May with a female and a juvenile — a family group.
The birds disappeared in the dense brush, and Liadis and Yeany couldn’t photograph them. Two days later they returned with nets and were able to capture and band the juvenile hatched this year — the first proof that the species has bred successfully in Pennsylvania.
About Swainson’s warbler
As songbirds go, Swainson’s warblers are somewhat drab. Brown, with a yellow underbelly, the little birds are well camouflaged in the dense underbrush of rhododendron and mountain laurel, where, unlike many other warblers that are in the treetops, they forage for insects amid the leaf litter with their straight bills.
“Nick and I have said that it would be more aptly named the sword-billed warbler because of that feature,” Yeany said.
Yeany said there are two different breeding populations for the species. One set breeds in bottomland forests and wetlands within the southeastern United States. A separate population breeds in the forests of the Appalachian Mountains, like West Virginia, and Yeany said presumably the birds found in Pennsylvania are from that group.
In August and September, Liadis said, the warblers migrate from their breeding grounds to winter in either the Yucatan Peninsula in Mexico or Cuba, Puerto Rico, and Jamaica.
These birds are often described as “secretive” because they spend so much of their time on the forest floor, hidden in the understory. Kate St. John, a longtime birder and author of the “Outside My Window” blog calls them “skulkers.” She said she’s driven as far as 200 miles to try to see one, but has only ever heard their calls.
“It’s a tribute to David Yeany and Nick Liadis’ knowledge, skill, and persistence that they have documented the first breeding record in Pennsylvania,” St. John said.
Habitat and climate change
According to the American Bird Conservancy, Swainson’s warbler numbers may be increasing, but the bird is threatened by habitat loss.
Yeany said the warbler is predicted to lose about a quarter of its current range under future climate scenarios. But it’s also predicted to gain about 60% of new range because of climate change. It could be like the yellow-throated warbler and red-bellied woodpecker which have had northward range expansions.
Yeany said Swainson’s warbler is vulnerable in West Virginia and critically imperiled and endangered in Maryland.
“Our surrounding states to the south have elevated their conservation status, which means if we get an established population, we’re going to need to have a responsibility to conserve that as well,” Yeany said.
Bear Run Nature Reserve is already a well-preserved, over 5,000-acre property owned by the Western Pennsylvania Conservancy. Yeany said he’s already spoken with the stewardship director there about putting up some signage to alert visitors and birders about the importance of the habitat.
“I think that this will place greater emphasis on maintaining that mature forest condition, keeping invasives out, and maintaining that dense shrub layer,” Yeany said. “I think what we’re doing there now is the reason why the birds are there.”
Liadis said this discovery of Swainson’s warbler breeding in Pennsylvania underscores the need to conserve habitat and encourage people to make their yards bird-friendly.
“I’m really big on encouraging folks to do a number of things that can benefit songbirds,” he said.
He said collaboration with the area’s birders will also be key as he and Yeany continue to search for and study the species at Bear Run and other properties with suitable habitats. They will also be sharing feather samples with researchers looking for genetic information to study migration and breeding patterns.
What’s in a name
Swainson’s warbler was named in 1834 by John J. Audubon after his friend, the British naturalist William John Swainson. Swainson has several other birds named for him, including a sparrow, hawk, thrush, and a subspecies of toucan, among others.
Swainson’s warbler is on a list of 155 birds with honorific or eponymous names that the group Bird Names for Birds would like to see re-named. The idea is to decouple bird names from the colonialism and the racism associated with them, and instead call birds by their characteristics.
For example, Swainson’s antcatcher is now known as the white-bellied antbird and Swainson’s fire-eye as fringe-backed fire-eye, though not as a result of the current Bird Names for Birds movement.