Kirtland's Warbler range. Map courtesy of Birds of North America, https://birdsna.org, maintained by Cornell Lab of Ornithology
The handsome yellow-and-gray Kirtland's Warbler is named for Dr. Jared Kirtland, whose Ohio farm provided the first specimen in 1851. Biologists finally discovered the first nest for the species in 1903, in northern lower Michigan.
Kirtland's Warbler has one of the smallest breeding ranges of any North American bird. Almost the entire population breeds in north and central Michigan, with small (but increasing) numbers in Minnesota, Wisconsin, and Canada. These birds winter only in the Bahamas and the Turks and Caicos Islands.
For optimal breeding success, the Kirtland's Warbler requires large areas — more than 160 acres — of dense young Jack Pine trees that are six to 15 years old and five to 20 feet high. Scientists speculate that the age and size of the Jack Pine trees may be important in concealing the birds' nest, which is built on or near the ground. This early successional habitat was historically created by wildfire, but fire suppression programs almost eliminated the habitat and the species itself.
Endangered Species Act Success
Kirtland's Warbler was one of the first species to be listed under the Endangered Species Act after the ESA's passage in 1973. By 1987, the number of singing males had dropped to a low of 167. But thanks to habitat management programs that include managed burns, clear-cutting, and seeding of Jack Pines — plus constant control of nest-parasitizing cowbirds — the number of singing males rebounded to over 2,300 by 2015.
In October 2019, after 50+ years on the endangered species list, the Kirtland's Warbler was delisted by the U.S. Fish and Wildlife Service. The population has increased five-fold since the early 1950s, far surpassing the recovery goal for the species.
Keeping the Kirtland's Warbler population on the road to recovery will require continuing programs to create young Jack Pine forests and reduce nest parasitism by Brown-headed Cowbirds. Meanwhile, since the 1990s, a multi-agency monitoring program in the Bahamas has been conducting research to learn more about the bird's winter habitat. Loss of habitat on the wintering groups is another threat to the species' long-term recovery.
Kirtland's Warbler by Robert Royse
David Ewert, ABC's Kirtland's Warbler Program Director, started researching the species in the Bahamas in 2002 and has made some interesting discoveries. "As on the summer nesting grounds [in the Great Lakes region], it selects dense, early-successional habitat," he says. "Kirtland's Warblers are most frequently seen where there are higher concentrations of certain fruiting shrubs such as wild sage, black torch, and snowberry, which the warblers prefer for feeding."
Kirtland's Warblers are also seen on active goat farms in the Bahamas. Possibly the goats help to create the early successional habitat favored by the birds.
The Growing Threat of Turbines
Poorly sited wind turbines are a growing hazard to the Kirtland's Warbler, especially those around the species' fall migration route in the Great Lakes region. The Icebreaker Wind project, which would place a precedent-setting wind energy facility in Lake Erie, is a particular concern. To that end, in December 2019, ABC and Black Swamp Bird Observatory filed suit in federal court, asserting that the agencies involved failed to comply with environmental laws during their evaluation of Icebreaker's impacts.
Working for Kirtland's Warbler
In spite of substantial gains made for the species, it's not out of the woods yet. “This warbler is still among the rarest migratory songbirds in North America," says Shawn Graff, ABC's Vice President for the Great Lakes Region. "It is conservation reliant, meaning that continued management efforts are imperative for the population to hold its ground and continue to expand.”
ABC is playing a lead role to ensure needed conservation efforts for the Kirtland's Warbler continue, including with a wide range of partners through the Kirtland's Warbler Conservation Team. The team is developing a comprehensive business plan that addresses the warbler's needs across its life cycle and sets a course for post-ESA success.
ABC also has launched a long-term fund to generate sustainable revenue for research, habitat development, and community outreach throughout the species' range. This revenue will complement ongoing efforts of state and federal agencies to maintain the highly specific habitat the Kirtland's Warbler needs for breeding, and to limit impacts from Brown-headed Cowbirds. This private-public partnership represents a new model for addressing the ongoing needs of a delisted, conservation-reliant bird species.
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