With its natural habitat mostly gone, one of North America's rarest songbirds has found a surprising workaround: It's thriving in the industrial pine plantations of the southeastern United States.
Farmed loblolly pines are becoming the main breeding habitat for the mysterious Swainson's warbler, according to a recent study published in Bird Conservation International. The discovery is welcome news for the secretive bird, a species of high conservation concern. It's also a bit ironic, says study author Gary Graves, curator of birds at the Smithsonian Museum of Natural History.
"The pine industry doesn't care about conservation," Graves says. "But quite by accident, they're growing and generating more habitat for this bird than the federal government, state governments, and NGOs combined."
One Tough Bird
Swainson's warbler has been adapting to the South's changing landscape ever since it was described and sketched by famed ornithologist John Audubon in the 1830s.
The tiny, primrose yellow birds were first discovered in dense thickets of giant sugarcane known as canebrakes, where they could nest out of sight and forage for insects on the swampy ground. The Cornell Lab of Ornithology describes the bird as "skulking." "If it weren't for its loud, ringing song, the presence of the species in many areas would go completely undetected," the lab's website says.
Canebrakes once covered the southeastern U.S., but European settlers quickly converted them to agricultural land.
With their natural habitat decimated, Swainson's warblers moved into bottomland forests on public lands that were often logged for timber, according to Graves. But after conservation efforts against clear-cutting in the 1970s, these young forests began to mature and lose the thick underbrush that the songbirds used for protection. (Watch a video about sustainable logging.)
"All of sudden you have this paradox of public land managers managing for old-growth forests and, in the process, removing habitat for a bird right on the cusp of being an endangered species," says Graves.
Swainson's warblers have a bit of a Napoleon complex, according to Graves: They weigh in at half an ounce and could fit in your palm, but they require territories of anywhere from 7 to 45 acres (3-18 hectares) each. That's part of the reason why their numbers are so low. The total population is estimated at 90,000.
With their native and adopted habitats removed, the warblers were thought to be in decline—until they started popping up in tree farms.
On a pine plantation, timber is grown, harvested, and regrown every 25 to 35 years in a mosaic of patches, which means there are always some patches that are the right age for Swainson's warblers. Sunlight beaming through the thin canopies supports bushy thickets that make ideal hiding and foraging locations.
"It's one of these Goldilocks situations: not too tall, not too short, not too thin, not too thick, just right. The forest ground is messy and impenetrable, and really quite ugly, to a human. But it's just beautiful to them," said Graves.
A Warbler in a Pine Tree
Loblolly pine farms cover 30 million acres (12 million hectares) in the South, which in recent decades has become the world's "wood basket" and supplier of cheap pulpwood. Current projections suggest their total acreage could double in the coming decades.
Pine plantations took off in the South in the 1970s, replacing degraded farmland as well as native habitats for wildlife. That, along with their unnatural configuration—monocultures in neat rows, four or five feet (1-1.5 meters) apart, and intensively managed for optimal timber growth—led ecologists to characterize the tree farms as "biological deserts."
The revelation that they can support Swainson's warblers demonstrates the importance of considering "alternative habitats" in conservation, including those that are historically unheard of, says ornithologist Thomas Benson of the University of Illinois in Champaign.
But the presence of one rare species of songbird doesn't mean industrial pine plantations are teeming with life. Though they benefit certain wildlife, the farms are "species-poor systems overall," says Mark Ashton, a forest ecologist at Yale University.
Frogs and amphibians have lost wetland habitat to pine plantations, according to Mike Wilson, a research biologist at the College of William and Mary. Even among birds, the red-cockaded woodpecker, an endangered species, remains a vexing symbol to the timber industry, which has replaced the woodpecker's longleaf pine habitat with the more profitable loblolly variety.
Providing the habitat for a songbird on the brink of becoming endangered is a rare feather in the industry's cap, says Graves. In the interests of keeping its bird tenants happy and burnishing its own image, it ought to avoid environmentally harmful practices like spraying herbicides, Graves argues. (Read about the failed attempt to convert longleaf pines to biofuel.)
"They then can say, We can't create habitat for every species, but we're doing a damn good job of creating habitat for some, and a few rare ones too," Graves says.