House Finches face multiple disease threats
FeederWatch data show that House Finch populations have declined dramatically since the mid-1990s, and recent research from California suggests that West Nile virus may be contributing to the declines. Researchers Anne Pellegrini and colleagues reported on the survival rates of House Finches in Sacramento County before and after the arrival of West Nile virus in the area*. The researchers took blood samples from wild House Finches and tested mosquitoes (the primary vector for the virus) for infection in order to pinpoint the arrival of the disease. They first detected infected mosquitoes in the county in late 2004. Before the virus arrived, annual survival for House Finches from 2001-2004 was approximately 0.59 (meaning that 59% of birds would survive from one year to the next, on average). Following the arrival of West Nile virus, annual survival probabilities dropped to 0.47 from 2005-2008. The researchers concluded that West Nile virus was contributing to further population declines in House Finches in their area.
West Nile virus first appeared in North America in the New York City area in 1999. It rapidly spread across the continent and affected many species of birds in addition to humans, horses, dogs, and other animals. Crows, jays, and other members of the Corvid family were particularly hard hit by the disease. Laboratory studies revealed that approximately 60% of House Finches infected with West Nile virus were killed by the infection. But 40% recovered, and the presence of antibodies against the virus in apparently healthy wild finches suggests that recovery is possible in the wild as well. Further, these survivors have immunity against subsequent infections.
In addition to West Nile virus, House Finches have proven highly susceptible to the “House Finch Eye Disease” caused by the bacteria Mycoplasma gallisepticum, and to avian pox, caused by a virus. Although the combination of these three challenges has certainly contributed to widespread population declines, the House Finch remains one of the most common birds seen at feeders in much of the continental U.S. and southern Canada.
For more information about House Finches, visit the species account on All About Birds.
* Pellegrini, A.R., S. Wright, W. K. Reisen, B. Treiterer, and H. B. Ernest. 2011. Annual survival of House Finches in relation to West Nile virus. Condor 113:233-238.