SPRING 2002/VOLUME 16, NUMBER 2

Southern Exposure
By ANDY DAVIS AND SONIA ALTIZER
New study shows unexpectedly high prevalence of House Finch eye disease in Atlanta, Georgia

Female House Finch from Atlanta, Georgia, showing mild symptoms of House Finch eye disease.
For nearly a year, we were part of the Cornell Lab of Ornithology research team working to help understand the dynamics of House Finch eye disease (mycoplasmal conjunctivitis). By trapping House Finches, marking them with leg bands, and observing known individuals, we helped to document the proportion of infected finches and their fates in and around Ithaca, New York. When we relocated to Emory University in Georgia last fall, we decided to begin gathering comparable data from a southern site.

Because Georgia is assumed to be the winter destination of many migrant House Finches, we expected to see large numbers of finches. Based on preliminary analyses from the House Finch Disease Survey, we also expected to find a higher proportion of finches with conjunctivitis than we had in New York. As it turned out, we found fewer House Finches than we expected. And even though we expected to find a high proportion of House Finches with symptoms of disease, we were stunned by the magnitude of disease prevalence that our study revealed around the Emory campus in Atlanta.

Our data suggest that House Finches are not as common around the Emory campus as they are around the Lab of Ornithology. We observed flocks of up to 12 birds at a time on or near the Emory campus, with average flock size ranging from 1 to 5 birds. In Ithaca, winter flocks of up to 40 finches were observed, with about 14 finches per flock on average. Also, feeder use in Atlanta seems sporadic. We suspect that during Georgia's warm winters, natural food sources are so abundant that House Finches may not depend as heavily on bird feeders as they do in the North.

Figure 1.
 Prevalence of House Finches with signs of mycoplasmal conjunctivitis in Atlanta, Georgia, and Ithaca, New York, during fall and winter 2001-2002. (Monthly sample sizes 18-45 in Atlanta; 64-252 in Ithaca.) The proportion of birds with symptoms of disease in Atlanta was unexpectedly high.

With trapping data from the Lab's House Finch team, we compared monthly changes from the northern Ithaca site with our southern one. Despite our lower sample sizes, the proportion of birds with symptoms was surprisingly high at our Atlanta site (Figure 1). During October 2001, approximately 75 percent of the finches we captured were infected. During the same month at the Lab of Ornithology, only one finch showed clinical signs of disease, out of more than 200 captured. The peak of the fall outbreak occurred in October in Atlanta, with lower proportions of infected birds in the following months. Meanwhile, no notable fall outbreak was reported in Ithaca, and diseased birds appeared increasingly after October.

We also noticed differences in the birds' symptoms during and after the fall outbreak. From August through October, many of the birds we captured showed severe symptoms (one or both eyes swollen shut, almost blinding the bird). These birds tended to be less mobile and had trouble flying and finding perches. However, after the fall epidemic, all the House Finches we saw or captured had relatively minor symptoms such as red swollen eyes, and fewer birds experienced simultaneous infections in both eyes. Clearly, we will need to collect more data to determine why the severity of infection varies depending on location and time of year.

We are planning to expand our project outside the city limits. Some homeowners have offered their backyard bird feeders as research sites. A few citizens outside the city have reported seeing 50 or more House Finches, indicating potential differences between the campus and other areas. With more data, we hope to determine whether patterns in Atlanta are consistent with those in surrounding areas.

Although our results from Atlanta showed very high prevalence of House Finch eye disease, many wildlife diseases fluctuate, with highs and lows occurring from year to year. It is therefore possible that the extremely high prevalence of disease that we observed last fall was related to long-term cycles and may not represent the average prevalence. Even so, our data suggest that either House Finches or the pathogen itself varied between the northern and southern monitoring sites.

We encourage bird watchers in the Southeast to participate in the House Finch Disease Survey. More observations from this underrepresented region will increase our understanding of the epidemic.

Andy Davis and Sonia Altizer are researchers in the Department of Environmental Studies, Emory University

Suggested citation: Davis, Andy and Altizer, Sonia, Southern Exposure. Birdscope, newsletter of the Cornell Lab of Ornithology, Spring 2002. <www.birds.cornell.edu>

For permission to reprint all or part of this article, please contact Miyoko Chu, Editor, Cornell Lab of Ornithology, 159 Sapsucker Woods Rd., Ithaca, New York. Phone (607) 254-2451. Email mcc37@cornell.edu