During the spring and summer, the brightly colored Golden-winged Warbler (Vermivora chrysoptera) inhabits forested landscapes in the Appalachian Mountains, the Great Lakes region, and adjacent southern Canada. Golden-winged warblers breed in forests comprised of a mix of young and more mature stands, old fields, shrubby wetlands, and disturbed areas where forests are regenerating, such as along powerline rights-of-way and small forest openings. They are closely related to Blue-winged Warblers (Vermivora pinus) and where the two species come in contact on their breeding ranges, readily hybridize, producing fertile offspring including Brewster's Warblers and Lawrence's Warblers. Especially in the Appalachian Mountains portion of their breeding range, Golden-winged Warblers have experienced dramatic population declines, and these declines have been attributed in part to hybridization with Blue-winged Warblers and maturing of forested landscapes.

Largely due to concern about populations in the Appalachian Mountains, Golden-winged Warblers have been petitioned for listing under the U.S. Endangered Species Act. They are currently also considered a Threatened Species under Canada's Species at Risk Act, and are afforded special conservation status in multiple states. Much of the concern about Golden-winged Warbler populations and what is known about their breeding ecology comes from studies conducted on the Appalachian Mountain population segment, yet this population segment currently contains only approximately 5 percent of the global population. In the western Great Lakes region, where the bulk of the global Golden-winged Warbler population breeds, relatively little is known about their population ecology and habitat relations. However, there is concern about issues related to hybridization with Blue-winged Warblers, consequences of climate change, distribution and abundance of suitable habitat, and population ecology and population affinity of Golden-winged Warblers on their wintering grounds in Central and northern South America. To begin to address some of these information needs, the Minnesota Cooperative Fish and Wildlife Research Unit built on the results of previous studies of Golden-winged Warblers in the western Great Lakes region to evaluate population dynamics and habitat relations, and currently is working to better understand affinity with wintering areas. David E. Andersen, Unit Leader for the U. S. Geological Survey at the Minnesota Cooperative Fish and Wildlife Research Unit, and Henry M. Streby, a NSF Postdoctoral Fellow at the University of California, Berkeley, are leading the research efforts.

From 2010-2012 at two study areas in Minnesota and one study area in southeastern Manitoba, researchers captured and attached miniature radio transmitters to female Golden-winged Warblers upon their return from wintering areas following spring migration. Those birds were followed to their nests, monitored for success of their nests and re-nesting attempts, and, for nests that produced fledglings, researchers attached transmitters to those fledglings prior to their leaving the nest. Fledglings were then monitored until they reached independence from adults and many of them were monitored for weeks after independence.

To date, efforts have produced some rather surprising results, which have implications for Golden-winged Warbler conservation and challenge some of what had been previously accepted as known about Golden-winged Warblers. For example, Golden-winged Warblers use relatively mature forest much more than had previously been recognized. Territorial males spend considerable time in relatively mature forest, a large portion of nests are located in relatively mature forest, and both male and female Golden-winged Warblers move fledglings under their care to relatively mature forest, where fledgling survival is high. Furthermore, where Golden-winged Warblers place their nests appears to be highly influenced by proximity to brood-rearing habitat. Early in the season, nests are more likely to be situated in relatively mature forest, where probability of nest success is lower, but where young produced from nests are likely to survive. Later in the season, nests are more likely to be placed in younger, shrubby stands, where the likelihood of producing fledglings is higher than in more mature forest, but where fledgling survival is lower as they move to brood-rearing habitat (i.e., relatively mature forest). This strategy seems to be one of adjusting risk based on the time remaining during the season to produce fledglings to independence?similar to financial strategies that accept higher risk early in one's financial timeline and minimizing risk as one approaches retirement.

Interestingly, Golden-winged Warblers also appear to employ obligate brood division, where females and males each take a portion of their brood to different areas during the brood-rearing period. Both male- and female-reared sub-broods use the same mature forest cover as brood-rearing habitat, but females move their sub-brood almost four times farther from the nest than males. Because most conservation plans for forest-nesting songbirds are based on where males defend territories and where females place nests, knowing what factors are related to fledgling survival and where adults move their broods can help provide a more complete understanding of how to incorporate considerations for Golden-winged Warblers and other forest-nesting songbirds into forest management plans. Based on the information derived from radio-marked fledglings and nests of radio-marked female Golden-winged Warblers, Streby and Andersen also developed estimates of full-season productivity (the number of young reared to independence) across study landscapes as a function of habitat relations. Those models allowed the scientists to evaluate the relative influence of managing different cover types (e.g., upland forest versus shrubby wetlands) to benefit Golden-winged Warblers, and also to evaluate how different management activities (e.g., timber harvest of different sizes and configurations) might influence population dynamics. Finally, based on estimates of survival and reproduction, the researchers estimated that study populations in Minnesota were growing rapidly, and the population studied in southeastern Manitoba was not consistently self-sustaining, suggesting the importance of regional, meta-population dynamics in maintaining the western Great Lakes Golden-winged Warbler population.

The Minnesota Cooperative Fish and Wildlife Research Unit is continuing to work on issues related to Golden-winged Warbler ecology and conservation with a variety of collaborators (U.S. Fish and Wildlife Service, Minnesota Department of Natural Resources, and the Golden-winged Warbler Working Group, to name a few). Efforts are currently focused on better understanding the relationship between wintering areas and population dynamics across their breeding range, how Golden-winged Warblers might be expected to respond to climate change on their breeding grounds, and what implications for other species (e.g., American woodcock [Scalopax minor]) there might be when landscapes are managed with considerations for Golden-winged Warblers. The Unit expects that the results of current and ongoing research can inform conservation strategies for forested landscapes in the western Great Lakes region, and provide additional insight into population ecology of songbirds dependent on diverse forest landscapes.

Each month, the ONB features articles from Cooperative Fish and Wildlife Research Units across the country. Working with key cooperators, including WMI, Units are leading exciting, new wildlife research projects that we believe our readers will appreciate reading about.