Press Releases

"FeederWatchers" Help Track Decline of Crows and Chickadees

Cornell Lab of Ornithology Study Shows Whereabouts of Last Winter's Birds

December 5, 2003

Autumn 2003, Ithaca, NY - Last winter, in West Nile virus-afflicted parts of the country, American Crow counts dropped to a 15-year low. Other species, including chickadees, were also scarce, while still others appeared in record-high numbers.

    How do researchers know this? Because during that time, more than 16,000 people counted the birds that visit their feeders and sent this information to scientists at the Cornell Lab of Ornithology, where it was collated and analyzed to determine the status of North America's feeder birds.

    The observers are volunteers for Project FeederWatch, a winterlong survey of North American birds that visit backyard bird feeders, organized and managed by Cornell and Bird Studies Canada. "FeederWatchers" represent a range of ages and backgrounds, but all of them share a passion and concern for birds. They follow a specific protocol, designed by scientists and educators, choose "count days," record how many birds of each species they see, and note details about weather conditions. Then they provide this information to scientists at Cornell. "Thanks to the careful reports of these dedicated volunteers, we've been able to make some interesting observations concerning the whereabouts of birds across the continent," says David Bonter, project leader for Project FeederWatch. "Findings from last winter are particularly interesting.

    Bonter notes that the winter of 2002-2003 was one of extremes. American Crow counts fell to a 15-year low in the Midwest (Kentucky, Illinois, Indiana, and Ohio), a region hard hit by West Nile virus (WNV). Despite the decline there, though, the overall abundance of crows continued to be stable.

    Not so for other species. In their respective ranges, numbers of Black-capped and Carolina chickadees, among the most familiar and beloved bird species, also fell to a 15-year low. "Counts were 15 percent lower this year than last, and down 18 percent compared to the previous 14-year average," says Bonter. He adds that chickadees in the Midwest were especially scarce;their numbers were 32 percent lower than their historic FeederWatch average.

    The Midwest, which by far showed the most dramatic drop in chickadee numbers, was a WNV hotspot with a high number of human cases reported last year. Is West Nile virus responsible for the declines in bird populations? Wesley Hochachka, assistant director of the Cornell Lab of Ornithology's Bird Population Studies department and a data analyst for Project FeederWatch, cautions that little is known about how West Nile virus has affected chickadees and most other birds. "Chickadee declines were not limited to states with West Nile virus outbreaks," says Hochachka. "This suggests that the drop in numbers might be attributable to more than just West Nile virus." Further evidence against a WNV connection is that the declines were not sudden but rather follow a trend that began in 1998 and hit low points in 2001 and 2003. WNV only became widespread in North America in the past two years.

    House Finch numbers also declined last winter. This decline follows a decade-long fall in House Finch numbers that can be tracked to House Finch eye disease, a bacterial infection that began affecting House Finches in the early 1990s. This disease often leads to blindness and death, and tends to keep flocks of House Finches small. However, when Hochachka and his colleagues closely tracked the movements of the disease, they found that the occurrence of the infection was not abnormally high this past winter, leaving the researchers to conclude that factors yet to be determined likely contributed to last winter's declines.

    Other absences are less of a mystery. Common Redpolls, Evening Grosbeaks, and White-winged Crossbills and other species collectively known as "irruptive winter finches" typically reside year-round in Canada and parts of the extreme northern United States. Based on 15 years of FeederWatch data, these species rather predictably shift their ranges farther south in alternate years, probably in response to food availability. These southward "irruptions" can bring large flocks of these northern birds to feeders in the United States. Last year's FeederWatch season was predicted to be a slow one for these winter finches south of their year-round range, and the prediction was upheld. However, because the birds remained farther north last winter, the irruption pattern dictates that FeederWatchers be on the lookout for these species in more southerly locales this season.

    FeederWatch did find an increase in some species last winter. For example, both Cooper's and Sharp-shinned hawk counts were at an all-time high. These birds of prey are relatively easy to track because they regularly visit feeders, where they specialize in dining on smaller bird species. Why the increase in their numbers? Many possibilities exist, but Bonter and Hochachka theorize populations could still be rebounding from the use of the pesticide DDT in the last century, which inadvertently caused devastating declines in birds of prey.

    Other species on the rise last year, according to FeederWatch data, include Red-bellied Woodpecker and Northern Cardinal; both were at an all-time high in the Midwest, even in the presence of West Nile virus. Downy Woodpeckers and Mourning Doves were seen in slightly greater numbers throughout their ranges.

    "It's truly amazing what we've learned from the remarkable dataset provided by Project FeederWatch," says Bonter. "And to think that it exists solely because so many people are willing to take a little time to tell us which birds are visiting their bird feeders through the winter makes it more remarkable still. We are so grateful for their help."

     The more volunteers submitting bird counts to Project FeederWatch, the more scientists can learn about feeder bird populations. Participants receive a research kit that includes instructions, bird-feeding tips, a colorful poster of common feeder birds, a bird-counting days calendar featuring photos taken by FeederWatchers, and more. A $15 fee ($12 Lab members; $25 Canadians) helps defray the cost of operating the study. To learn more about Project FeederWatch, including how you can become a FeederWatcher, call (800) 843-2473. In Canada, contact the Canadian partner, Bird Studies Canada, at (888) 448-2473. Visit FeederWatch on the Web at www.birds.cornell.edu/pfw.

The Cornell Lab of Ornithology is a nonprofit membership institute whose mission is to interpret and conserve the earth's biological diversity through researcher, education, and citizen science focused on birds.