North America’s Rarest Warbler Comes Off the Endangered List

Habitat restoration and invasive species trapping have helped Kirtland’s recover in its central Michigan home

Kirtland's Warbler
Joel Trick, USFWS

Earlier this week, the U.S. Fish and Wildlife Service officially delisted Kirtland’s warbler from the endangered species list. The bird, which only nests in a few counties in central Michigan with smaller populations in Wisconsin and Ontario, was one of the first species added to the list in the early 1970s. Almost fifty years of efforts between federal and state agencies, timber companies and conservation organizations has increased its population enough that officials no longer believe it is in immediate danger of extinction.

Even in pre-settlement times, Kirtland’s warbler was something of a rare bird. The 6-inch-long songbird with a blue-gray back and yellow tummy was first catalogued by naturalists in 1851. It wasn’t until 1903 that that an intrepid biologist discovered its unique nesting grounds in the forests of central Michigan. The bird has very specialized breeding requirements. It will only build its cup-shaped, grass nests beneath the lowest branches of dense stands of young jack pines, between 6 and 22 years old. The species also requires about 300 to 400 acres of habitat before it will colonize a site. Jack pines, however, have “seratonous” cones, or cones filled with a flammable resin. They won’t open unless they are burned, meaning that decades of fire suppression in Michigan and elsewhere greatly reduced Kirtland's habitat.

The other major problem the species faces is a native parasite called the brown-headed cowbird. In pre-settlement times, the cowbird followed herds of bison in the shortgrass prairies of the central U.S., picking seeds out of their dung. To keep up with the herds, they also developed a neat trick; instead of making their own nests, they kick eggs out of other birds’ nests and lay their own before moving on, essentially tricking other species into raising their chicks. As humans killed off the bison and changed the landscape, filling the U.S. with cows, the cowbirds moved out of their native range and now inhabit almost all of North America north of Mexico. While cowbirds have impacted many species of native birds, they hit Kirtland’s warbler particularly hard.

The one-two punch of fire suppression and cowbird parasitism drove Kirtland's numbers down. Biologists first realized the bird was in trouble in the 1950s. A survey of singing males estimated that about 1,000 of the birds remained in Michigan in 1961. By 1971, however, the population had plummeted to around 400 birds. In 1973, it was one of the first animals on the newly established endangered species list and the USFWS established a multi-agency Kirtland’s warbler recovery team to spearhead its revival. Still, the species struggled, and by 1987, counters only found 200 singing males during their annual survey.

Slowly but surely, however, conservation teams diligently trapped cowbirds during nesting season and teams cleared and planted young jack pines, increasing potential habitat for the birds, which spend the winter in the Bahamas. About 190,000 acres of public land has been set aside in central Michigan for the bird’s conservation, with about 38,000 acres managed each year to attract the warblers. Annually, roughly 4,000 acres of mature jack pine forest is cut and replanted with 2-year-old saplings to make sure habitat remains available for the birds in the future.

All that work paid off, and by 2001 the species reached 1,000 pairs. Over the following decade, small colonies of the birds dispersed to appropriate habitat in Wisconsin and Ontario. Today, there are an estimated 2,000 pairs of the birds breeding in the upper Midwest, twice the recovery goal.

“The effort to recover the Kirtland’s warbler is a shining example of what it takes to save imperiled species,” Margaret Everson, principal deputy director of Fish and Wildlife Service, says in the press release. “Truly dedicated partners have worked together for decades to recover this songbird. I thank them for their efforts and applaud this historic conservation success.”

Even though the species is off the endangered list, it still requires annual habitat management to keep its numbers healthy, William Rapai, chairman of the Kirtland’s Warbler Alliance, tells Keith Matheny at the Detroit Free Press.

Some conservationists, however, want a little insurance to make sure people don’t forget about the rare species that calls Michigan home. Rapai tells Neal Rubin at The Detroit News that the Kirtland’s warbler should be elevated to Michigan’s state bird, which is currently the American robin. While the robin is a fine bird, it’s also found in every state in the U.S. The Kirtland’s warbler, the rarest warbler in the U.S., can only be reliably found in Michigan and draws nature-loving tourists to the state from around the world. There’s even a monument to the bird in the town of Mio. “Show me a monument to a robin in Michigan,” says Rapai, who points out that, technically, the selection of the robin as state bird by schoolchildren in 1931 expired long ago. “The Kirtland’s warbler is Michigan’s story.”

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