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The Biology Of Bird Feeders

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Travis Wilcoxen
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Infected house finch. The avipoxvirus causes the bumpy growth seen on the beak.

People love to feed birds. It’s a great way to bring wild animals right into your backyard, and it’s a big industry, too, with more than $3 billion dollars spent annually on birdseed alone. There are hopper feeders, suet feeders, hummingbird feeders, and many more. There’s even a market dedicated to keeping squirrels out of the feeders, with products for sale like the Squirrel Be Gone and Squirrel Buster Plus. As popular as bird feeding is, few people think about negative impacts that the feeding could have on the birds.

“We definitely saw that although, in general, the birds at the feeder sites had some health benefits of the seed, they also tended to contract disease at a higher rate and spread disease at a higher rate than at the sites without the feeders," said Dr. Travis Wilcoxen, associate professor of biology at Millikin University. "Just like any animal that comes into close contact with other ones in high densities, it increases the risk of disease transmission, and that’s certainly what we saw at our feeder sites.”

Wilcoxen became interested in the effects of bird feeding on wild populations, so in 2011 he set up six research sites in forested areas of central Illinois. Three of the sites had feeding stations, and the other three did not. Over the course of three years, Wilcoxen and his team caught more than 2,000 birds of multiple species to determine the effect of the bird feeders. They found that sites with the feeders had increased rates of diseases, but had more body fat. The feeders were removed after the study was complete, and the birds were sampled again after the feeder removal to see if they had grown dependent on the feeders. The birds were fine, indicating that they were not dependent.

So if the birds don’t need our help, and bird feeders can increase the rate of disease, should we stop feeding birds altogether?

“I don’t think people should stop feeding birds," Wilcoxen said. "I think, in general, we found positive influences of the feeding on the health of the birds with the exception of the small percentage of the birds that contracted disease. I think there are some things that can be done to remedy that, perhaps cleaning feeders more regularly. We also think that not filling it up every day, maybe leave it empty for a day or two, that should reduce the total number of birds at the site, but it shouldn’t really lose the species that come to visit, but it will probably reduce the transmission rate because there won’t be as many animals there in one place.”