Kirtland’s Warbler Conservation Team addresses decline in songbird’s population

A team of conservation experts from state and federal agencies and nonprofit groups is undertaking a long-term plan to stabilize the population of the once-endangered Kirtland’s warbler.

The 2025 census of the colorful songbird indicates a decline in the population. According to the recent survey, there are 1,477 breeding pairs of Kirtland's warblers in Michigan, which is home to 98% of the global population. Another 12 pairs were counted in Wisconsin, for a global population of 1,489 pairs, with Ontario's numbers yet to be reported.

The last census, in 2021, estimated the global population at 2,245 pairs.

The decline is projected to continue over the next few years before the Kirtland’s Warbler Conservation Team’s efforts can stabilize the population through innovative strategies to manage the bird’s habitat. The team is a collaborative network of partner organizations including the Michigan Department of Natural Resources, U.S. Fish and Wildlife Service, U.S. Forest Service, Wisconsin Department of Natural Resources, American Bird Conservancy, Huron Pines and others.

“This is a situation we’ve been monitoring and addressing for several years now,” said Erin Victory, a wildlife biologist and Kirtland’s warbler management coordinator for the Michigan DNR. “From a habitat management perspective, we anticipated a decline in the population and have been taking action to address it. We are confident we have enough tools and resources available to us, collectively within the conservation team, to reverse the decline and stabilize the population.”

The Michigan survey was conducted June 6-26 in the northern Lower Peninsula and Upper Peninsula. The census resulted in:

• 814 pairs of Kirtland’s warblers on DNR-managed land in the northern Lower Peninsula.
• 597 pairs on Forest Service land in the northern Lower Peninsula.
• 49 pairs on DNR-managed land in the Upper Peninsula.
• 17 pairs on Forest Service land in the Upper Peninsula.

Small numbers of the songbird also live in Wisconsin and Ontario (in 2021, Ontario reported 22 pairs).

One reason for the decline in the bird’s population is a reduced acreage of suitable breeding habitat. The ground-nesting Kirtland’s warbler relies exclusively on young jack pine forests to breed, with the vast majority of the birds living on designated state- and federally-managed acreage in northern Lower Michigan. But there currently aren’t enough young jack pine stands available to maintain a stable population of Kirtland’s warblers, so the state and federal agencies will adjust the tree-harvesting strategy to create more breeding habitat in designated management areas.

The Michigan DNR has worked closely with the Fish and Wildlife Service, the Forest Service and other groups for decades to create habitat for the Kirtland’s warbler through jack pine plantings (the bird will only nest in jack pine stands that are about 6-20 years old). The goal is to maintain at least 1,000 pairs of Kirtland’s warblers. By selling timber to clearcut mature jack pine followed by planting jack pine seedlings, land managers provided a consistent amount of young habitat to support this goal. The strategy mimics how jack pine naturally regenerates after wildfire by creating a mosaic of thickets and openings. Many other early-successional plant and animal species benefit from this commitment on the landscape.

However, in recent years it has become evident that previous management practices need to be updated. Early intensive efforts to create habitat ramped up in the late 1980s and 40 years of implementing jack pine plantings have resulted in a majority of the management areas with 30- to 40-year-old jack pine stands. Because these stands are intentionally planted at higher densities for better habitat compared to other types of planted stands, they are not commercially marketable for clearcutting until they are at least 60 years old. This has left land managers with less opportunity to create young habitat over the last decade.

“While a population decline is not what we wanted to see this census, it is encouraging that we already understand the principal cause and conservation team members are taking steps to address the issue,” said Steve Roels, coordinator of the Kirtland’s Warbler Conservation Team and Kirtland’s warbler program director for the American Bird Conservancy.

The conservation team is developing a 10-year Breeding Range Conservation Plan to effectively manage the habitat. The primary strategy is to use novel approaches to cut jack pine stands in the surplus 20- and 30-year age classes, in addition to 60-year-old stands, to ensure annual habitat goals are met consistently. To the extent possible, the younger timber will be sold as mulch or as a renewable energy resource on the biomass market. Land managers are also evaluating the feasibility and safety of increasing prescribed fire use.

“This strategy continues to create habitat and also allows the 40-year age class to continue growing and become merchantable. If we kept trying to harvest from the 40-year age class we would be perpetuating the problem,” said Jason Hartman, silvicultural specialist for the Michigan DNR. This strategy will benefit local economies, Kirtland’s warblers and other species associated with the jack pine ecosystem.

Other strategies in the management plan include transitioning away from jack pine plantations where possible in favor of lower-cost natural regeneration and partnering with university researchers to evaluate new habitat management techniques. The plan also calls for periodic monitoring of brown-headed cowbird nest parasitism. Cowbirds lay eggs in the nests of Kirtland's warblers and other bird species. The larger cowbird chicks out-compete warbler chicks for food, which causes them to die, while the warbler parents unknowingly raise the cowbird chick.

Unforeseen factors affect the Kirtland warbler’s population as well. Victory referenced a 2023 hailstorm that wiped out half of the jack pine seedlings at a DNR-contracted nursery that were slated for planting and wildfire in the breeding areas that can change the amount of habitat. Additionally, hurricanes during migration and dry winters on the species’ wintering grounds in the Bahamas can stress or kill birds, with fewer birds returning to northern Michigan the following year.    

“The decline in the Kirtland’s warbler population is likely due to a decline in available breeding habitat, but there are other factors that we can’t control that are associated with higher bird mortality,” Victory said.

The Kirtland’s warbler was federally endangered for nearly 50 years. The population dropped to fewer than 200 pairs in the 1970s and again in the 1980s when the population was restricted to only 14 townships in six counties in northern Lower Michigan. Thanks to a decades-long, collaborative effort to recover the species by federal, state and private partners, the bird was removed from the federal endangered species list in 2019.

“The Kirtland’s Warbler Conservation Team is a highly collaborative group that has been working to ensure the survival of the Kirtland’s warbler for more than 50 years,” said Phil Huber, a wildlife biologist and chair of the conservation team. “I am confident that this group will continue to do what is necessary for this at-risk species and other plants and animals in the jack pine ecosystem.”

The Kirtland’s warbler remains a state-threatened species in Michigan because it is conservation-reliant, meaning it will not persist without intensive management. The majority of the population nests in a 10-county area in the northern Lower Peninsula, primarily from Grayling to Oscoda.

Kirtland's warbler surveys have been conducted in Michigan since 1951. A full survey, or census, is conducted every two to four years. State and federal agency staff and volunteers survey jack pine nesting areas, listening for singing males advertising and defending nesting territories. Each recorded male is presumed to have a mate, so the number of males also indicates the number of breeding pairs.

While Victory said surveys in coming years may show the bird’s numbers coming close to or even dropping below the population threshold of 1,000 breeding pairs, she’s confident the population will rebound with the conservation team’s habitat management strategies.

“The real strength of the management of the Kirtland’s warbler lies in the collective efforts of the conservation team,” Victory said. “The collaborations and partnerships that we’ve leveraged among our state, federal and private partners will continue to be a driving force behind maintaining a sustainable population of the Kirtland’s warbler and other species in the jack pine ecosystem.”