Laura Erickson's For the Birds

Friday, October 19, 2007

A bit more about cats

I just got my copy of an extraordinary book--Silence of the Songbirds by Bridget Stutchbury. It is a very important book about bird conservation, by a scientist with a great mind and a great heart. Here's a brief excerpt:
A tiny, pale warbler, a female common yellowthroat, had been caught in mid-May while she was nest building and was fitted with a tiny backpack that held a radiotransmitter. Over the next week researchers followed her movements for a few hours every day as she finished her nest, laid eggs, and began incubating her clutch of four eggs. One day, she was gone and her eggs were stone cold.

Scott Tarof, a postdoctoral researcher at the University of Wisconsin, went out that afternoon to help a graduate student find out what had happened to their female. The bird's radio signal was coming from the pasture across the road from the study site. The two walked into the pasture thinking they would find the radio tag lying on the ground, but were puzzled when the signal suddenly started coming from the far end of the pasture. As they walked in that direction, the signal moved again; this time it was several hundred yards away in the opposite direction. There was no common yellowthroat to be seen or heard, so they thought they were going crazy or maybe the equipment was not working properly.

After a few hours of frustrating false leads looking for the radio tag in the hot sun, they finally got a steady signal from a clump of grass in the corner of the pasture. They zeroed in on the signal only to find a chewed-up transmitter in a pile of cat poop. The female warbler had been eaten by someone's cat, and Tarof had unknowingly been following the cat that still had the bird, and its radio tag, inside it.

To estimate the numbers of birds killed, homeowners in Michigan were asked to count up the dead animals their cats brought home. On average, each cat killed about one bird a week, and though this may not sound like much, the damage adds up because there are so many free-ranging cats near homes and farms. The six hundred cats in this study would have killed more than six thousand birds during a typical ten-week breeding season alone. A similar study in Wichita, Kansas, asked homeowners to bag the contents of the litter box so researchers could later search through the feces looking for feathers. They found bird remains in about 10 percent of the samples, even though the homeowners had not reported seeing their cat bring back a bird in recent days. This suggests that kitty is not as innocent as owners think and that surveys of cat predation underestimate the true scale of the problem. When the Wichita study ended, the homeowners were asked if, given the results of the study, they would now keep their cats indoors; 73 percent said no.

Cats are not to blame for the songbird decline, but keeping cats indoors will mean that birds nesint in woodlots near farms and homes will have a better chance of staying alive and producing a healthy number of offspring.