The United States has watched some iconic native birds disappear during the past 100 years or so, including the passenger pigeon, the Carolina parakeet, the heath hen, the dusky seaside sparrow and possibly the ivory-billed woodpecker.
The Kirtland's warbler almost joined them, driven to the brink of extinction last century by habitat loss and nest parasites. Its decline was so dramatic that it became one of the original species listed under the U.S. Endangered Species Act (ESA) in 1967.
But now, thanks to that protection and decades of work by conservationists, this tiny warbler is no longer in crisis. It's still on the endangered species list, but the U.S. Fish and Wildlife Service (FWS) has formally proposed "delisting" the species due to its recovery. This comeback is being widely hailed as yet another triumph of wildlife conservation under the ESA.
"This is a story of success," says Jamie Rappaport Clark, president and CEO of the nonprofit Defenders of Wildlife, in a statement. "Habitat loss and nest parasitism nearly drove the Kirtland's warbler to extinction. But thanks to the collaboration and scientific research that the Endangered Species Act requires, we were able to recover this songbird for future generations."
Birds of passage
The Kirtland's warbler would likely be extinct if not for the Endangered Species Act, conservationists say. (Photo: Andrew Cannizzaro/Flickr)
The Kirtland's warbler is a 6-inch songbird with a bluish-gray back and a bright yellow breast. It nests in Michigan, Wisconsin and Ontario, and migrates along the Southeastern U.S. coast to its wintering habitat in the Bahamas.
It has very specific nesting criteria, resulting in one of the smallest breeding ranges of any North American migratory songbird. It nests only on the ground during spring, near low-hanging branches in large stands of young jack pine trees, which must be 5 to 20 feet tall and 6 to 22 years old. The age of a tree is critical, the FWS explains, although biologists aren't really sure why. It's possible the birds need low branches near the ground to help conceal their nests. Before jack pine trees reach 6 years old, the lower branches aren't large enough to hide the nest, and after about 15 years, the lower branches begin to die.
Where's the fire?
These requirements may sound nitpicky, but they worked well for the species until relatively recently. Large stands of jack pines are plentiful in northern Michigan's sandy soils, where they were historically scorched by wildfires every few decades. Fire is required for jack pine cones to fully release their seeds, so these periodic blazes helped remove older trees while also encouraging the growth of new saplings. This ensured a supply of 6- to 22-year-old trees for the warblers to use as nesting sites.
In the 20th century, however, humans unwittingly broke this cycle by suppressing wildfires, which were once thought to harm the environment. This loss of vital nesting habitat was compounded by another threat: the brown-headed cowbird, a brood parasite that replaces its host's eggs with its own, tricking the host parents into raising its chicks. It's a native bird, not an invasive species, but its trickery combined with the loss of habitat proved too much for Kirtland's warblers to handle on their own.
An 'amazing comeback'
The warblers were among the first U.S. wildlife identified as being at risk of extinction, prompting their addition to the country's inaugural endangered list in 1967. The entire population of Kirtland's warblers fell to a low of 167 pairs in 1974, and again in 1987, before the revival built up steam. State and federal authorities developed a long-term plan to conserve young jack pines, and to trap brown-headed cowbirds within the warblers' habitat. By 2011, this had helped the species rebound to a record high of 1,828 pairs, surpassing the recovery goal of 1,000. As of the most recent count in 2015, there were more than 2,000 pairs.
In light of this comeback, the FWS is proposing the warbler be delisted as a federally endangered species. It will accept public comments on the proposal until July 11, and make a final decision by April 2019.
But while this would remove the Kirtland's warbler from the U.S. endangered species list, the FWS notes the birds will still need protection indefinitely. The nonprofit Kirtland's Warbler Alliance will help raise funds to cover the annual costs of conservation programs, the Associated Press reports, while the Michigan Department of Natural Resources will take over cowbird control from the FWS. If these management efforts continue, the population of Kirtland's warblers is expected to remain stable for 50 years.
And as some U.S. lawmakers decry the ESA as unnecessary, many conservationists say the Kirtland's warbler offers further proof the law is still working — as it already did for other recovered species, like American alligators, bald eagles and brown pelicans. "This pretty little songbird's amazing comeback from the brink of extinction is a testament to the success of the Endangered Species Act," says Noah Greenwald, endangered species director for the nonprofit Center for Biological Diversity, in a statement. "Contrary to the self-interested claims of congressional Republicans, this 45-year-old law is working to save species.
"Without it," he adds, "we would have lost the warbler forever."