Photo credit: Dollie M. Stover

A male Golden-winged Warbler, captured after responding to broadcast calls of another male.

On May 8, 2002, I was working on Coal River Mountain in Raleigh County, West Virginia, hoping to capture my first Golden-winged Warbler of the day. Using a tape, I broadcast the golden-wing's zee bee bee bee call. The mountaintop where I was standing had been blasted off to gain access to coal, rock, and soil. Now that the vegetation was returning to an early successional stage with pole-sized trees, it was typical habitat for the rapidly vanishing Golden-winged Warbler. But the first bird to respond to my tape was a male “Brewster's Warbler”—a hybrid between a Golden-winged Warbler and a Blue-winged Warbler, distinguishable by its wingbars and white throat and breast.

Hybrids are relatively rare and often make up less than one percent of the golden-wing and blue-wing populations in southern West Virginia. But their presence could have significant implications. The blue-wing has been expanding northeastward into the range of the Golden-winged Warbler and has locally displaced golden-wings from much of their former range in New England, New York, and the southern Appalachians. Yet the mechanism of how Blue-winged Warblers erode Golden-winged Warbler populations is not fully understood. Hybridization is believed to favor Blue-winged Warblers and has been postulated as a major contributing agent to the decline of golden-wings.

To better understand the mechanisms of species replacement, Dollie Stover, chief naturalist at the Southern West Virginia Bird Research Center, and I have been banding golden-wings, blue-wings, and their hybrids and recording detailed behavioral observations over the past 10 years. We've also contributed relevant data to the Lab's Golden-winged Warbler Atlas Project. This conservation project has been mapping the distribution of golden-wings, blue-wings, and their hybrids.

Photo credit: Ronald A. Canterbury

Despite typical habitat for Golden-winged Warblers, hybrids seemed to be everywhere.

When the Brewster's Warbler responded to my tape with an aggressive call—a rapid stutter followed by a lower buzzy note—I quickly erected my mist net. As I moved away from it, the Brewster's flew in and was captured. I banded it with a U.S. Fish and Wildlife Service band imprinted with a unique number (2150-58252) and headed for the next singing male one-tenth of a mile away.

There, I found a male Brewster's Warbler with the same plumage and aggressive behavior as the male I had just banded. I assumed that it was the same bird, but when I checked its legs, I saw that it was unbanded. I quickly banded this bird as well, dismayed to find two territorial Brewster's Warblers in such close proximity.

I was beginning to think that I was in some mysterious “white-throated” Golden-winged Warbler population. To my relief, the next four birds that I found were golden-wings. However, I was soon puzzled again when my seventh bird of the morning, within a mere mile, was another Brewster's. Such frequent encounters with hybrids across such a short distance were unprecedented in all my years of field work in this region.

Like other areas with mountaintop removal in the southern West Virginia coalfields, Coal River Mountain may favor a higher proportion of hybrid phenotypes and expanding Blue-winged Warbler populations. Preliminary data show that golden-wings appear to favor the older contour mines at higher elevations that were mined in the 1960s and early 1970s, but blue-wings are replacing golden-wings on intact mountaintop sites.

I didn't observe any Blue-winged Warblers on Coal River Mountain. However, I have not yet studied the entire area and blue-wings do inhabit the surrounding valley and lowlands.

In 2003, I plan to use the protocol for the Lab's Golden-winged Warbler Atlas to cover all mountaintop removal and valley-fill sites on Coal River Mountain and other sites. I'd like to know whether mountaintop mining creates so-called sink habitats, where not enough young are produced to offset adult mortality, and to document whether these areas have a higher proportion of hybrids and blue-wings than other upland habitats in southern West Virginia. This work will help establish a hybrid index and quantify how many Golden-winged Warblers remain in the Paint Creek Watershed, an area where replacement and local extirpation have been ongoing since the early 1970s.

This research is made possible by generous grants upport from the West Virginia Division of Natural Resources Nongame Wildlife Program

Ron Canterbury is an assistant professor of biology at Concord College in West Virginia and a collaborator with the Lab's Golden-winged Warbler Atlas Project.

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