The Lab's latest citizen-science initiative investigates why these colorful birds are vanishing

As we approach the final season of the Cerulean Warbler Atlas Project (CEWAP), the Cornell Lab of Ornithology is continuing to amass large amounts of data that are helping us create an atlas of Cerulean Warblers throughout their breeding range. We have received a tremendous amount of cooperation from the U.S. Fish and Wildlife Service (USFWS) in regions 3, 4, and 5, numerous Partners in Flight (PIF) contacts, and many other interested biologists and amateur birders. The funding made available to CEWAP allowed us not only to produce research materials and recruit many participants, but also enabled us to hire field assistants to make extensive surveys in almost every state within the cerulean's range. We are so pleased with the success of CEWAP that we've decided to continue this conservation-based research by applying the same approach to a new species of concern.

The Golden-winged Warbler is another Neotropical migrant whose numbers are declining, and it shares some of the same characteristics as the Cerulean Warbler. The USFWS has initiated a status assessment of the Golden-winged Warbler, as they have for the Cerulean Warbler. This is an effort to compile all that is currently known about the species to help biologists decide whether we need to take further steps to protect the bird. The Golden-winged Warbler is listed as a priority species in at least 14 PIF physiographic regions of North America, and it ranked second among all Neotropical migrant species in terms of immediate conservation concern in the Northeast. These priority rankings are based on a small total population and significant declining trends; the species has declined in numbers by 7.6 percent each year since 1966 throughout the Northeast. Considerable controversy exists regarding the historical status of this bird in some regions, however, and further declines in its population seem very likely unless a successful management plan can be implemented in the near future.

The decline of the Golden-winged Warbler correlates with two factors–loss of breeding habitat as the process called succession converts shrubland into secondary forest, and the arrival of the Blue-winged Warbler. Golden-winged Warblers use early succession fields with a predominance of herbaceous cover and scattered shrubs following abandonment of farmlands, clear-cutting, or fire. Much of this habitat in the north- eastern United States, where golden-wings were once common, is now covered by secondary forest due to reforestation. In many parts of the eastern United States, the habitat necessary to sustain a breeding population of these birds is almost completely gone. Concurrent with the loss of habitat, Blue-winged Warblers began to expand northward and eastward into the Golden-winged Warbler's range. Dominance between Golden-winged and Blue-winged warblers appears to vary across the range of overlap and could contribute to the Golden-winged Warbler's decline in some areas.

The northward expansion and resultant zone of overlap has led not only to increased competition, but to widespread interbreeding between the Golden-winged and Blue-winged warblers. In central New York, about 4 percent of the territorial males are hybrids. Hybrids occur in two distinctly different phenotypes called "Brewster's" Warbler and "Lawrence's" Warbler. So, unlike the "Yellow-shafted" and "Red-shafted" races of the Northern Flicker, whose individual characteristics appear to be blended together when they interbreed, golden-winged and blue-winged hybrids look like completely different birds and were originally thought to be different species.

The Golden-winged Warbler is expanding into Ontario, northern Minnesota, and Manitoba. In these locations an abundance of new habitat is being created as farms are abandoned and woodlands are clear-cut for timber. Blue-winged Warblers have not yet arrived in these areas. In older portions of the golden-wing range, some suitable habitat still remains, for example, along powerline right-of-ways. Hybridization in these areas may be the most significant factor causing the decline of the Golden-winged Warbler there. How frequently these two species hybridize throughout their range is not known. The North American Breeding Bird Survey relies almost totally on the distinctive songs of each species to identify birds, but hybrids and pure phenotypes can sound alike. Therefore, the need has arisen for compiling and creating a Golden-winged Warbler atlas, which will determine the frequency of hybridization by visually examining all of the birds counted in areas in which the two species' ranges overlap.

To identify key safe haven sites for declining Golden-winged Warblers, we need to understand the extent of this hybridization and the species' population status across their range. This is best accomplished through the atlas approach pioneered successfully by CEWAP. So, the Lab of Ornithology and Ithaca College have formed a partnership to study the Golden-winged Warbler. John Confer, an associate professor in the Biology Department at Ithaca College, is taking the lead on this new endeavor with the help of the Lab's own Ken Rosenberg.

John Confer has conducted field studies on golden-wings for more than 20 years, looking at factors that influence the breeding success of these birds. He has published many papers on golden-wings and their interactions with Blue-winged Warblers. He has also formed and now heads a Golden-winged Warbler working group within PIF to organize current research and monitoring efforts. With the Lab's ability to organize a citizen-science atlas program like CEWAP, obtain data via the Internet, and conduct analyses of spatially related data, these two organizations with their different avenues of expertise should complement each other nicely. This season we will test and refine a protocol developed last year to assess the population status of golden-wings and blue-wings, map the hybridization zone, and identify management options for these species.

We plan to use the 1999 field season as our pilot year for the Golden-winged Warbler Project and make the following season the first full-fledged year of the project. If you have some knowledge about Golden-winged Warblers, can identify them in the field, and think you might like to help us test protocols this season, please contact us at the address, phone number, or e-mail address listed below.

Don't forget we are still continuing CEWAP for another season and would especially like help from people in the midwestern and southeastern parts of the Cerulean Warbler's range. We hope present CEWAPers will continue with the project and think about helping us with this new Golden-winged Warbler endeavor as well.