The Kirtland’s warbler is a small songbird that is native to the jack pine forests of northern Michigan. This rare bird has a very specific habitat requirement, nesting only in young jack pine stands 5-20 years old and approximately 6-15 feet tall. This limited nesting habitat led to the Kirtland’s warbler being listed as an endangered species in the 1960s.
Background on the Kirtland Warbler
The Kirtland’s warbler (Setophaga kirtlandii) is a small songbird about 6 inches long and weighing less than half an ounce. The male has a gray back and bright yellow underparts with black streaks. The female is duller overall with light yellow underparts. This warbler species was named after Dr. Jared P. Kirtland, a 19th century naturalist from Ohio.
Kirtland’s warblers have very specific nesting habitat requirements. They nest exclusively in young jack pine stands that are 5-20 years old with terrain varying from six to 15 feet in height. This kind of habitat was historically created naturally by wildfires in northern Michigan. As the jack pines aged, the warblers would abandon the stands in search of new, younger jack pine habitat.
Parts of northern Michigan and Wisconsin as well as Ontario, Canada make up the breeding range for the Kirtland’s warbler. These warblers are migratory, wintering in The Bahamas from November to March. They return to their Michigan breeding grounds starting in mid-April.
Population Decline and Endangered Status
The Kirtland’s warbler population declined significantly in the first half of the 20th century. By the early 1960s, this species was on the brink of extinction with only about 400 singing males counted in 1971. This precipitous decline was caused primarily by loss of jack pine nesting habitat.
Wildfires that naturally created the 5-20 year old jack pine stands preferred by nesting Kirtland’s warblers were being suppressed. At the same time, large-scale logging was removing older jack pine forests and not being replaced by new growth. Farming in the Great Lakes area also led to jack pine habitat loss. The drastic reduction in available nesting habitat caused the Kirtland’s warbler population to crash.
In response to this crisis, the Kirtland’s warbler was designated as an endangered species under the Endangered Species Preservation Act of 1966, a precursor to the modern Endangered Species Act. This protective status made conserving Kirtland’s warbler habitat a top priority.
Habitat Management and Population Rebound
After being protected under the Endangered Species Act in 1973, a Kirtland’s Warbler Recovery Team including the U.S. Fish and Wildlife Service, U.S. Forest Service, and state conservation agencies developed a management plan to regenerate and conserve jack pine habitat. Timber harvesting and planting was used to mimic the habitat historically created by wildfires.
These habitat management efforts were very successful. The number of singing male Kirtland’s warblers increased from 1,000 in 1981 to over 2,300 by 2015. The total wild population including females and young birds likely approaches 5,000 birds today.
The Kirtland’s warbler Recovery Team established a population goal of 1,000 breeding pairs with 1,000 backups to maintain genetic diversity before considering delisting the species. The Kirtland’s warbler exceeded this minimum population threshold starting in 2007.
Kirtland Warbler Delisted from Endangered Status
In 2019, the U.S. Fish and Wildlife Service proposed removing the Kirtland’s warbler from the List of Endangered and Threatened Wildlife. This delisting proposal was made after nearly 50 years of habitat management and population monitoring showed the species had recovered sufficiently.
The proposal went through a public comment period and received support from the Michigan Audubon Society and other conservation groups. After final review, the Kirtland’s warbler was officially removed from the Endangered Species List in October 2019.
This delisting is considered one of the major success stories of the Endangered Species Act. The Kirtland’s warbler recovery is an excellent example of federal and state agencies and conservation groups collaborating to bring a species back from the brink of extinction.
Ongoing Habitat Management
Although no longer listed as endangered, the future of the Kirtland’s warbler is still dependent on active habitat management since natural wildfires are still suppressed. The U.S. Fish and Wildlife Service, U.S. Forest Service, and Michigan DNR will continue plans for timber harvesting, controlled burning, and replanting on public lands to maintain jack pine nesting habitat.
There are also efforts to provide more habitat diversity and encourage use of other young conifer stands besides jack pine. While the core breeding range will remain in northern Michigan, work is being done to provide additional habitat and expand the warblers’ range in the Lower Peninsula and Wisconsin.
Monitoring and research continue to track the Kirtland warbler population and habitat use. Banding provides information on nesting success, lifespan, and migration routes. The spread of brown-headed cowbirds that lay eggs in warbler nests is also being studied.
Despite now being delisted, the future of the Kirtland’s warbler is far from certain and will rely on continued habitat conservation and funding commitments. However, the recovery so far provides an exemplary model of endangered species management success.
Conclusion
In summary, the Kirtland’s warbler was listed as an endangered species in 1966 when the population declined to just a few hundred birds. This was caused by loss of the species’ preferred jack pine nesting habitat due to fire suppression and logging. After being protected under the Endangered Species Act, collaborative efforts by government agencies and conservation groups helped regenerate habitat and boost the warbler population above recovery goals. The Kirtland’s warbler was officially removed from the Endangered Species List in 2019 after nearly 50 years of protection. Ongoing habitat management and population monitoring will be critical to ensure the continued success of this conservation program in the future.
