Changes in U.S. Birds Documented by Citizen Scientists

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1. The spread of House Finch eye disease

Birders first reported House Finches with red, swollen eyes in Virginia and Maryland during 1993?94. Participants in the House Finch Disease Survey and Project FeederWatch tracked the new disease as it spread across the continent. Researchers used the data to demonstrate declines in House Finch numbers in the East and to study regional differences in the dynamics of epidemics.

2. Climate change and timing of nesting

Data from citizen scientists recording nesting observations show that Tree Swallows in North America are breeding earlier, coincident with an increase in spring temperatures. The egg-laying date advanced by up to nine days from 1959 to 1991.

3. Eastern Bluebird regional reproduction changes

By collecting data on Eastern Bluebirds, participants in The Birdhouse Network helped researchers examine how nesting patterns vary across the species’ range. The data revealed that the largest clutches at southern sites had lower hatching success than expected.

4. Decline of Evening Grosbeak

Evening Grosbeaks were common feeder birds when Project FeederWatch began in 1987. FeederWatchers’ counts showed that by 2006, the number of sites reporting Evening Grosbeaks declined by 50 percent. Where they remained, flock size had decreased by 27 percent.

5. Impacts of West Nile virus

West Nile virus arrived in North America in 1999. Breeding Bird Survey contributors provided data used by scientists to determine the impact of West Nile virus on 20 species across the continent. Seven species from four families (American Crow, Blue Jay, American Robin, Eastern Bluebird, Black-capped Chickadee, Tufted Titmouse, and House Wren) declined significantly—American Crows by as much as 45 percent in some areas. Only two of the seven species (jays and wrens) had recovered their numbers by 2005.

Eurasian Collared-Dove by Laura Erickson

6. Invasion of Eurasian Collared-Dove

Participants in the Great Backyard Bird Count, Project FeederWatch, and eBird have documented a dramatic range expansion of Eurasian Collared-Doves since the mid-1970s, when they were first introduced in the Bahamas. Visit www.eBird.org and click “view and explore data” for a map of recent reports.

7. Golden-winged and Blue-winged warblers

Data from the Breeding Bird Survey, eBird, and Golden-winged Warbler Atlas Project show links between Blue-winged Warbler range expansion, hybridization with Golden-winged Warblers, and local extinctions of golden-wings. This information helps them target “safe havens” where golden-wings can be protected.

8. Interesting population cycles

Data from Project FeederWatch showed that Common Redpolls don’t move continuously throughout winter. Rather, they use different wintering ranges in different years. FeederWatch and Christmas Bird Count data also suggest that Varied Thrush winter populations, within their normal range in the West, rise and fall in a two-year cycle. In contrast, the number of vagrant Varied Thrushes that turn up in the East and in southern California isn’t correlated with that cycle.

9. Effects of “sudden oak death” on birds

Breeding Bird Survey and Christmas Bird Count data are helping researchers predict future declines of oak woodland birds such as Acorn Woodpeckers and Oak Titmice due to the spread of sudden oak death. This disease kills coast live oaks and is of special concern in areas of California that have no other oak species.

10. Acid rain and Wood Thrush abundance

Data from Birds in Forested Landscapes, the Breeding Bird Survey, and government studies of acid rain and soil acidity, showed a strong link between high acidity levels and declining numbers of Wood Thrushes. Acid rain leaches calcium out of the soil. Birds that feed primarily on soil invertebrates may not be getting enough calcium for reproduction.

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