Ten years after the endangered Kirtland’s warbler was first documented in Wisconsin, state and federal conservationists say a record number of successful nests were observed in 2017.

But the 15 nests are still just a flicker of life compared to the thousands of Kirtland’s warblers in Michigan, where habitat restoration has been in the works for 40 years.

The endangered songbirds are very particular about where they will nest, and that contributes to the uncertainty about their future in Wisconsin.

In coming years, efforts to draw more Kirtland’s warblers to Wisconsin may shift north from the Adams County pine plantations where almost all of the nesting has occurred so far.

Adams County may be able to support more of the birds, or it may be near its capacity despite ambitious plans by a golf course developer to convert large swaths of existing pine plantation into a more natural habitat, state and federal officials said.

The state Department of Natural Resources and the U.S. Fish and Wildlife Service are giving more attention to Marinette County, where fledglings emerged from three nests this year. They are also watching a Bayfield County woods that had a successful nest in 2016, and parts of Vilas and Jackson counties where the birds have been spotted off and on since 2008.

“You never want all your eggs in one basket, no pun intended,” said Davin Lopez, a state Department of Natural Resources conservation biologist.

State and federal agencies have worked to carve out habitat for Kirtland’s warblers and protect them from predators.

The U.S. Department of Agriculture captures hundreds of brown cowbirds near Kirtland’s warbler nesting grounds to prevent the cowbirds from laying their eggs in warbler nests. The DNR has used recorded Kirtland’s warbler song to entice the birds. But more could be done.

“I don’t think we are near where we want to be or where we can be in terms of Wisconsin’s contribution to the overall recovery of the species,” Lopez said.

There may be hope for progress in Adams County as the Sand Valley Golf Resort moves ahead with plans for habitat restoration.

Developer Michael Keiser said Kirtland’s warblers were spotted this year on restored land around the golf course that opened this year on about 1,700 acres. Two more courses are set to open in 2018.

After rows and rows of red pine were cleared from the land, native plants were cultivated, but in some places the wild lupine and other natives sprung up from seeds that had been dormant in the sandy soil for decades, Keiser said.

“It was probably the coolest thing I’ve witnessed in my life,” Keiser said.

The developer has purchased another 7,200 acres next to the resort with plans to turn large swaths of it into open-to-the-public recreational land for activities like hunting, hiking and skiing. As part of that, Keiser wants to restore habitat for the Kirtland’s warbler and two other endangered species — the Karner blue butterfly and the slender glass lizard.

The plan faces challenges. The land is enrolled in a state program that defers payment of property taxes on land as long as it is managed for timber cutting. Knowing that the Sand Valley resort would generate income, it made sense to pay roughly $1.4 million in deferred taxes in 2014 when the initial acreage was withdrawn from the program and cleared, Keiser said.

But the rest of the 7,200 acres wouldn’t generate revenue to cover the roughly $7 million to take it out of production. Keiser said the law allows him to stop replanting trees for harvest on 20 percent of the land without penalty. He is considering ways to manage the other 80 percent in a way that allows timber cutting to continue while also improving wildlife habitat.

For example, instead of replanting harvested timber land with tight rows of red pine, it may be possible in some areas to allow jack pine to regenerate naturally or to plant trees in a less intensive pattern that improves habitat. Such land won’t provide maximum profit when it is cut, but it will satisfy the law, Keiser said.

Keiser said he would like to increase available habitat for the Kirtland’s warbler, Karner blue butterfly, and slender glass lizard. He’s working closely with state and federal conservation agencies, but the task is complicated.

The Kirtland’s warbler takes to stands of young jack pine punctuated by open areas. The Karner blue and the slender glass lizard thrive in a sunnier landscape — pine barrens, prairies and savannas without thick canopies.

Pete Fasbender, ecological services supervisor for the U.S. Fish and Wildlife Service office in Minneapolis, said he is most excited about the prospect for restoring barrens and savanna, which would support not only the Karner blue butterfly and the slender glass lizard but many other species that aren’t endangered but have been squeezed by development.

“This is what makes it more exciting to me, if you can manage for species in the pine barrens system,” Fasbender said. “Then you are managing not for one species but for a suite of species.”

Kirtland’s habitat doesn’t have as broad a benefit to other species, Fasbender said.

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Steven Verburg is a reporter for the Wisconsin State Journal covering state politics with a focus on science and the environment as well as military and veterans issues.