"Its beauty is of the quiet kind and its voice without melody," Thomas Sadler Roberts wrote of the golden-winged warbler (Vermivora chrysoptera) in his 1932 treatise The Birds of Minnesota. Though its insectlike beee-bz-bz-bz is not as elegant as the song of a thrush, this modest 3⁄10ths-of-an-ounce warbler is captivating. A dainty bird with golden wings, wearing a golden cap and a striking black mask, the golden-winged warbler is a special prize often found in shrubby swamps—places where you do not necessarily expect to see such beauty.
Current vs. Historic Breeding Range
Minnesota has less than 10 percent of the golden-winged warbler's breeding range, but it hosts an estimated 47 percent of the species' breeding population. The birds are Neotropical migrants, spending three to four months in the United States and Canada and wintering in Central and South America.
Golden-winged warblers are Minnesota snowbirds. These warblers spend three to four months, from mid-May to mid-September, in Minnesota before heading south. Recent research "suggests that most of Minnesota's golden-winged warblers winter in Nicaragua and to a lesser extent in Costa Rica," says Tom Will of the U.S. Fish and Wildlife Service, who has studied golden-wings on their wintering grounds.
This Neotropical warbler is relatively common in the north-central part of the state. Its breeding distribution extends from Sherburne and Chisago counties west to Otter Tail County, northeast to Lake County, and northwest to Roseau County.
The breeding population of golden-winged warblers has remained stable in Minnesota over the past 45 years, according to the North American Breeding Bird Survey, a joint project of the U.S. Geological Survey and the Canadian Wildlife Service. At the same time, its population has declined by more than 60 percent across the rest of its breeding range in the United States and Canada. According to the Golden-winged Warbler Working Group, a collection of experts focused on implementing a species conservation plan, the main reason for the bird's decline is habitat loss—including human development of wetlands and shrub lands and maturation of grassy fields and young forests.
The golden-winged warbler is listed as threatened in Canada, and it has been considered for listing in the United States. Here in Minnesota, it has no official endangered or threatened status, but the Department of Natural Resources designated it a species of greatest conservation need, largely because of its huge declines in other parts of its breeding range.
Lee Pfannmuller, chief author of the report Stewardship Birds of Minnesota, published by Audubon Minnesota, coined the phrase Minnesota's premiere stewardship bird for the golden-winged warbler. To justify the title, she states, "Although many Minnesotans think that bald eagles and common loons are our trademark in the bird world, other areas of North America support larger populations of these iconic species. Instead, it is the diminutive golden-winged warbler that finds more abundant habitat in Minnesota than anywhere else in the world. Indeed, our northern forests and wetlands support 47 percent of the species' global population."
The survival of this species may depend on effective management and conservation in our state. No other Minnesota bird may be so dependent on Minnesota for its survival.
Volumes of information have been gathered and compiled by the Golden-winged Warbler Working Group. The researchers provide a wealth of recommendations for management of the species in the Great Lakes region, based on their work outside of Minnesota. They describe the golden-winged warbler as "an early successional species that requires a somewhat unique habitat of sparse trees and shrubs with an herbaceous understory of grasses and forbs in either upland or wetland settings." Habitats with these characteristics are also typical places you find golden-winged warblers in Minnesota. These habitats can be found in shrubby wetlands, in upland shrub lands such as abandoned fields, or in recently logged young forests.
Even though golden-wings were observed singing and foraging in these habitats, a mystery remained. Where did golden-winged warblers nest and raise their young? Until recently, few nests had been found, and it had been impossible to follow fledglings after they left the nest. Fortunately, Henry Streby, Sean Peterson, and David Andersen of the Minnesota Cooperative Fish and Wildlife Research Unit have elucidated this mystery. They placed micro–radio collars on hundreds of golden-winged warblers from 2010 to 2012 at Tamarac and Rice Lake national wildlife refuges in Minnesota and at Sandilands Provincial Forest in Manitoba, Canada.
Female golden-wings, which are the sole incubators of a breeding pair's eggs, were trapped, fitted with radio-telemetry collars, and tracked back to their nests, where many fledglings were also fitted with collars and colored leg bands. Observations and telemetry tracking revealed that golden-wings were using shrubby wetlands, shrubby uplands, young forests, and mature forests. Most of the female birds tagged in shrubby wetlands were later found nesting in shrubby uplands, young forests, or mature forests, often near the edges of wetlands.
"When we tracked them," Streby says, "we were surprised to find that this shrub-land species spends a lot of time in mature forest during nesting and even prefers mature forest for raising fledglings."
The researchers have completed telemetry studies in two areas of the species' breeding range in Minnesota, and they hope to study more areas. "Our research has found that this species, like many others, is most productive in a complex forest landscape with patches of many different forest types," Streby says. The data suggests that golden-winged warblers like a patchwork of habitats, primarily combinations of shrubby wetland edges for foraging and song perches, shrubby uplands or young forests for nesting and foraging, and mature forests with shrubby understories for cover, nesting, and foraging.
The evidence suggests that the golden-winged warbler is indeed a Minnesota icon and symbol of stewardship. Minnesota is not only the land of lakes, but it is also the land of wetlands and multi-aged forests. Conservation of the golden-winged warbler can help ensure the future of these habitats and aid other bird species too. Ruffed grouse and American woodcock use these habitats. So do the sedge wren, veery, Nashville warbler, chestnut-sided warbler, and rose-breasted grosbeak.
Our state faces many changes in the habitats needed by golden-winged warblers. Fire suppression has allowed shrub-land habitats to become dense and overgrown.
The early successional stages following logging activity create open patches of shrubs and young trees, habitats similar to the open shrub lands where golden-wings thrive. The future of young forests is unclear as logging activity has waned in recent years.
A changing climate may also affect the species. The landscape mosaic that golden-wings require may move northward. Ecologists Lee Frelich and Peter Reich of the University of Minnesota expect the prairie-forest border, within the primary golden-wing range, to shift northeastward over the next 50 to 100 years. The Golden-winged Warbler Group suggests populations will move farther into Manitoba.
For now, though, Minnesota's populations of golden-winged warblers are healthy, and it is unclear how all these changes will ultimately affect them. We have some control over threats such as habitat management, while others such as climate change are less controllable.
Threats to golden-winged warblers also come from other animals. Predation of eggs, nestlings, and fledglings is a constant challenge to successful nesting by golden-winged warblers. Potential predators range from snakes to mammals to other birds.
Blue-winged warblers displace breeding golden-winged warblers when their breeding territories overlap and the two species hybridize. Blue-winged warblers are found in southeastern Minnesota with minimal overlap in their breeding distributions. Yet blue-winged warbler populations have been expanding in Minnesota, so it is likely the hybridization threat will continue.
Brown-headed cowbirds, ubiquitous throughout the Minnesota range of golden-wings, can also affect the warbler's reproductive success through brood parasitism. This is a clever behavior of brown-headed cowbirds in which females sneak their eggs into the nests of other birds. Brown-headed cowbird nestlings are larger than golden-wings, so they outcompete golden-wing nestlings for food. Luckily, telemetry studies have revealed that such parasitism affects fewer than 5 percent of golden-wing nests.
"We take very seriously the responsibility for managing a large portion of the world's golden-winged warbler population," says Rich Baker of the DNR. Speaking about the DNR State Wildlife Grants program that supported the telemetry work, he says the research findings "point to the need to manage the state's forests at a very large landscape scale, like the findings for Canada lynx, northern goshawk, and many other species." All of these species require development and implementation of management plans that include multiple habitat types in a landscape mosaic. "This is a unique challenge to Minnesota's forest and wildlife managers that requires increased coordination of management across ownerships," says Baker.
An example of a large-scale cooperative management effort is the conservation easement on more than 180,000 acres of forest agreed on by UPM Blandin and the state of Minnesota. Alexis Grinde, a doctoral student at the University of Minnesota–Duluth, has done a long-term study counting populations of breeding birds in a large area of this conservation easement before and after logging. Prior to logging in the mid-1990s, bird counts revealed no golden-winged warblers in hundreds of acres. Counts in 2013 revealed a large number of golden-winged warblers had colonized the area, which is now dominated by young aspen forests intermixed with shrubby wetlands and patches of mature forest. This area now provides a substantial amount of breeding habitat for golden-winged warblers.
For the time being, golden-winged warblers continue to colonize Minnesota's wetlands and forests. They will provide important ecosystem services by eating insects, such as caterpillars that eat leaves and inhibit the growth of trees, and by transferring tree pollen that gets stuck in their feathers as they forage. Insects are the best pollinators, but birds also contribute.
For their role in keeping ecosystems healthy, golden-winged warblers ask no reimbursement except a place to live and raise their young, and a safe pathway to snow-free winter homes—much like many Minnesotans.