A Golden Opportunity

Experts on Golden-winged Warblers convene to share research results and work for conservation

By Sara Barker

The Golden-winged Warbler is federally listed as a species of special concern and has been declining dramatically throughout the northeastern United States. Population declines are associated with loss of shrubland habitat, overlap with competing Blue-winged Warblers, and hybridization between the two species.

In 2004, researchers from around the continent joined forces to advance our knowledge of this declining species at a special symposium at the American Ornithologists? Union annual meeting in Quebec City, Canada. Major research themes included genetics, habitat relationships, and conservation. The Cornell Lab of Ornithology contributed nearly complete results from the Golden-winged Warbler Atlas Project (GOWAP), the only range-wide study of this species that incorporates a population assessment and map showing the hybrid zone where golden-wings and blue-wings overlap.

Kate Neville and Rachel Fraser from Queen?s University gave talks relating to genetics and hybridization. Many researchers have assumed that hybrid females may be at a reproductive disadvantage. If that?s the case, theory predicts that the sex ratio of their offspring might be skewed. Using genetic techniques, Neville found that the sex ratio of the nestlings of hybrids was 50:50, suggesting that hybrid females are reproductively healthy. Understanding hybrid survivorship and reproduction will go a long way in helping us understand how hybridization is influencing changes in populations of Golden-winged Warblers.

Rachel Fraser, the symposium organizer, is a visiting research fellow in the Lab of Ornithology?s Evolutionary Biology Program. Her work focuses on hybridization and mate-choice decisions of blue-wings and golden-wings. Until now, researchers have estimated hybridization levels based on paired birds they see in the field. Sometimes, however, the birds mate with additional partners other than the one with whom they share a nest. By conducting genetic work to determine parentage of nestlings, Fraser is improving the accuracy of hybridization estimates and is documenting how gene flow will influence these species given the recent range shift and overlap.

Three talks explored habitat associations on a regional scale. Amber Roth works for the Wisconsin Department of Natural Resources and is a state coordinator for GOWAP. Using data from the Wisconsin Breeding Bird Atlas and GOWAP, she found that golden-wings prefer aspen clear-cuts, and lowland deciduous shrubs such as alder and dogwood, and willow swamps. In contrast, only 2 percent of golden-wings were in coniferous habitats.

John Confer from Ithaca College discussed how the Sterling State Forest in southern New York is the only area where golden-wings and blue-wings have coexisted for more than 50 years with little genetic mixing. They inhabit managed utility right-of-ways and old upland fields undergoing succession. Golden-wings also nest in swamp forest in the absence of blue-wings. These habitats are similar to areas where Golden-winged Warblers have been extirpated after the expansion of blue-wings in other areas of the Northeast. Confer is investigating whether habitats in the Sterling Forest are sources (places good for reproduction) or sinks (areas where many golden-wings may attempt to breed, but fail).

Jake Kubel from Pennsylvania State University studies golden-wings near State College, Pennsylvania. This area has frost pockets of natural ?mini-shrub­land? that do not need to be managed to remain in this stage of succession. In comparison with oak forests, he found a higher rate of reproductive success in clear-cuts with aspen cover where patches of rough-stem goldenrod occur near dense shrubs. His results suggest that clear-cutting may provide better habitat than managed utility right-of-ways with the proper forest cover type and presence of goldenrod.

Three studies investigated the potential benefits of reclaimed mine sites. Abandoned coal mines create a mosaic of early successional habitat within contiguous forest, mimicking natural disturbance at the landscape scale. Lesley Bulluck from the University of Tennessee found golden-wings in the Tennessee Cumberland Mountains associated mostly with sites reclaimed 6?20 years prior to her study. Laura Patton, from the University of Kentucky, found breeding golden-wings on reclaimed lands at lower elevations (393?783 meters), when previously they were thought to be rare and restricted to high elevations on Black Mountain in Kentucky. Proper management of these sites could propagate important golden-wing breeding habitat in some of the most southern regions of their range.

Ron Canterbury from Concord College, who studies golden-wings at old coal mines in West Virginia, suggested that elevation and slope are significant predictors of density and nesting success. Virtual replacement of golden-wings by blue-wings is occurring within 5 years in lowland sites, whereas for the last 13 years there appears to be a stable coexistence at upland sites on old contour mines. Ron stated that vast mountaintop removal mining sites mimic lowland sites, with a higher percentage of blue-wings and hybrids.

Looking at the larger picture, Dave Buehler from the University of Tennessee discussed the U.S. Fish and Wildlife Service status assessment. Both the assessment and GOWAP concur that loss of early successional habitat is the greatest contributing factor to golden-wing decline in the southern Appalachians, whereas in the Northeast both loss of habitat and hybridization with blue-wings are threats. The assessment warns that numbers may be starting to decline even in past golden-wing strongholds such as Ontario, Minnesota, Wisconsin, and Michigan, and populations will become less viable if they become isolated.

According to Tom Will of the U.S. Fish and Wildlife Service?s Midwest region, the Natural Resources Research Institute in Duluth estimates that golden-wings in Minnesota are common and not declining within the state. Because managers in the Midwest have the perception that golden-wing populations are stable, they are reluctant to commit to increasing the population at the potential expense of forest interior species. In Minnesota there are also debates over which habitat type best supports the species. Meanwhile, Partners in Flight has placed the Golden-winged Warbler on its Watch List and has set an objective of doubling the continental population over the next 30 years. GOWAP hopes to provide more data in the future to address some of these forest management questions.

A common thread seemed to develop within this symposium: golden-wings appear to be using different habitats regionally. In the coming year, GOWAP hopes to shed some light on habitat features that golden-wings use to select where to breed in a larger landscape context. We also plan to collaborate with Rachel Fraser and the Lab?s Evolutionary Biology Program to build a genetic atlas, helping to provide the underlying genetic population structure behind our hybrid index map. We hope to strengthen the connection between state conservation agendas and range-wide objectives when creating management plans for Golden-winged Warblers.

As this group of researchers looks for more clues, state and provincial governments will continue to take the lead in protecting golden-wing populations and critical habitat. As a follow-up to the symposium, two meetings will be held within the next year to help coordinate and facilitate golden-wing research, monitoring, and conservation in the immediate future. We commend Rachel Fraser for initiating this important cooperative effort and look forward to continuing our contribution to the conservation of the Golden-winged Warbler.

Sara Barker is project leader of the Golden-winged Warbler Atlas Project.

for additional information about Golden-winged Warblers see the Online Bird Guide at
www.birds.cornell.edu/programs/AllAboutBirds/BirdGuide/Golden-winged_Warbler.html

To participate in the Golden-winged Warbler Atlas Project, see www.birds.cornell.edu/gowap, email to forest_birds@cornell.edu, or call (607) 254-2473.

 

For permission to reprint all or part of this article, please contact Laura Erickson, editor, Cornell Lab of Ornithology, 159 Sapsucker Woods Rd., Ithaca, NY, 14850. Phone: (607) 254-1114. email: lle24@cornell.edu