Wisconsin habitat work hoped to save troubled Connecticut warbler

WASHBURN — State and county officials in Wisconsin are conducting emergency habitat work this fall in an 11th-hour effort to bring back more Connecticut warblers, the little songbird that has declined severely from the state's northern pine forests in recent years.

Wisconsin Department of Natural Resources and Bayfield County foresters will work this fall and next year to remove brush from stands of mature jackpines in hopes to recreate the kind of habitat the little yellow birds need to nest when they return to Wisconsin next spring.

The Connecticut warbler has been declining for a half-century, down 60% nationally, declining nearly 9% annually in northern Minnesota and down 80% in Wisconsin.

“This bird is in trouble, and it needs help fast,” said Ryan Brady, DNR conservation biologist and the state’s bird monitoring coordinator, in a statement Wednesday announcing the effort.

Brush removal this year and next will open the forest understory and encourage the growth of blueberry and other ground cover to restore the bird’s preferred natural conditions. The sparrow-sized birds nest on the ground and generally feed on the ground, searching for insects. But they prefer to be among tall — more than 20 feet — jackpine in Wisconsin.

“We’re trying to create additional habitat for Connecticut warblers while still meeting all (timber harvest) goals and objectives for the property,” said Andrew O’Krueg, a forester with the Bayfield County Forestry and Parks Department.

Connecticut warblers were once fairly common across northern Wisconsin pine forests. But a 2021 survey of 60 sites where they had been found before found only one nesting site, and a survey this spring found only three nesting pairs across their core habitat area of Bayfield and Douglas counties.

The warblers, which were never known to nest in Connecticut, are just hanging on in Minnesota and Canadian black spruce and tamarack bog forests, but have seen among the steepest decline of any neotropical songbirds.

In addition to problems in its spring nesting areas, it’s believed habitat loss in the bird’s wintering grounds 5,000 miles away in South America is the biggest reason the bird has declined more than 60% in recent years. Many of the birds winter in the Gran Chaco, the second-largest forest in South America after the Amazon, that stretches across parts of Argentina, Bolivia, Brazil and Paraguay.

Brady is co-leading a group of state and international partners to develop a rescue plan for the species that’s also looking at importing resting habitat along their migration routes each spring and fall.

The Natural Resources Foundation has also added the Connecticut warbler as a priority species to receive funding from Great Wisconsin Birdathon proceeds, according to Craig Thompson, who contributes to DNR’s bird conservation efforts. Thompson is working with international bird conservation partners to raise awareness of the need to protect the Gran Chaco’s forests for migratory birds and resident wildlife.

“Our challenge is to simultaneously address multiple threats to this bird across its vast hemispheric range before it’s too late,” Thompson said.

In Minnesota, the bird has been declining at an average rate of 8.5% since 1995. Once considered simply hard to find due to its remote nesting sites in bogs, it's now becoming outright rare.

Alexis Grinde, a bird researcher for the University of Minnesota Duluth's Natural Resources Research Institute, has said that the Connecticut warbler is now declining faster than any other bird studied in Minnesota's Chippewa and Superior national forests.

In northern Minnesota, spruce and tamarack are declining, in part due to the eastern larch beetle infestation that's killing tamarack trees. Climate change also appears to be impacting spruce bogs.

The Connecticut warbler is a small gray-hooded bird with a bold white eye ring, yellow chest and belly and olive back. Younger birds and females have more muted colors than males. During summer nesting season, they live in jack pine and black spruce forests primarily in northern Wisconsin.

In Minnesota, they are known to nest across the northern tier of counties, especially from St. Louis County north and west to Lake of the Woods County.

Connecticut warblers are marathon fliers. Canadian researchers documented the birds, which weigh half an ounce, flying nonstop for 48 hours over open ocean as part of their journey to wintering grounds in South America.

Meanwhile, the annual "State of the Birds" report was released Wednesday by the Cornell Lab of Ornithology. The report is compiled by more than 30 scientific groups across the U.S. and is a snapshot of the nation's bird populations.
Among the findings in the report:

• More than half of U.S. bird species are declining. 
• U.S. grassland birds are among the fastest declining with a 34% loss since 1970.
• Waterbirds and ducks in the U.S. have increased by 18% and 34% respectively during the same period.
• 70 newly identified "tipping point species" have each lost 50% or more of their populations in the past 50 years, and are on a track to lose another half in the next 50 years if nothing changes. They include Rufous hummingbirds, golden-winged Warblers and the black-footed albatross.