MADISON, Wis. (AP) — Conservationists in Wisconsin say they've spotted a record number of nests from the endangered Kirtland's warbler this year, a decade after the songbird was first spotted in the state.

Fifteen nests have been found so far in Wisconsin, The Wisconsin State Journal reported. However, thousands of Kirtland's warblers are in neighboring Michigan, where habitat restoration has been underway for 40 years.

The birds are particular about where they nest, which contributes to the uncertainty about their stay in Wisconsin.

The birds were first discovered in Wisconsin in the central part of the state. But the Wisconsin Department of Natural Resources and the U.S. Fish and Wildlife Service are now focusing on counties in the northern part of the state where the birds have been spotted.

"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 are working to create more habitat area for Kirtland's warblers and to protect the birds from predators.

For example, the U.S. Department of Agriculture has captured hundreds of brown cowbirds, which lay their eggs in Kirtland's warbler nests, near the endangered bird's nesting grounds. The state has recorded the Kirtland's warbler song to lure the birds.

In the central Wisconsin city of Nekoosa, the Sand Valley Golf Resort is also moving ahead with plans for habitat restoration. Developer Michael Keiser said the birds were seen on restored land around the golf course that opened this year on about 1,700 acres. Keiser also purchased 7,200 acres next to the resort, with plans to turn large swaths of it into open-to-the-public recreational land.