 |
|
|
House Finch Disease Update
As many of you know, since November 1994 we have been tracking the spread of an eye disease epidemic (caused by the bacterium Mycoplasma gallisepticum) in eastern House Finch populations, with the help of FeederWatchers, Lab members, and other interested people who are taking part in the House Finch Disease Survey. By October 1996 we had received about 22,000 data forms from participants reporting on the presence or absence of disease symptoms in the House Finches and other species visiting their feeders. In November 1994, 18 percent of 742 participants in the Mid-Atlantic region between Maryland and Massachusetts reported seeing infected House Finches, but only three participants out of 366 reported seeing a diseased bird in the Midwest region from Alabama and Mississippi north to Michigan and Wisconsin. The accompanying graph summarizes how the disease spread among House Finches in a 24-month period in these two regions. In the Mid-Atlantic region the proportion of observers reporting conjunctivitis increased steadily in the first year and now fluctuates seasonally. During the breeding season the reported incidence of disease decreased, but from August onward, when the young birds disperse, the incidence of disease reports increased again, reaching the maximum numbers of diseased birds by midwinter. By October 1996, 35 percent of observers had already reported seeing a House Finch with conjunctivitis.
In the Midwest region the reported incidence of disease remained below 10 percent of participants until July 1995, but then disease reports increased rapidly from 7 percent in July 1995 to 31 percent in February 1996, a level very similar to that in the Mid-Atlantic region. Now, reported disease levels seem to fluctuate in parallel in these two regions and both were at 32 percent in October 1996. That month diseased birds were being reported farther west still, especially from Nebraska. We received our first Nebraska report in March 1996. Unfortunately, we have very few participants in Nebraska, the Dakotas, Kansas, or Oklahoma, so without additional observers we cannot track in detail any further expansion of the disease in this region. The results we are obtaining with the help of our 2,863 volunteer observers are truly unique. In order to better understand how this disease spreads, how it affects House Finches and other bird species, how the disease is transmitted, why certain individuals are affected but not others, whether surviving birds have different traits than birds that die, why other passerine species seem less susceptible, whether the Mycoplasma gallisepticum strain in House Finches can reinfect turkeys, and more, we need more help. This help is now coming from two sources: you, the observers; and Barry Hartup, a doctor of veterinary medicine, who just started working on his Ph.D. thesis under the supervision of George Kollias, professor of Wildlife Medicine at Cornell University. As part of his thesis, he and I will analyze your data. So keep on sending your forms.
|
