Friday, October 30, 2009

Part 2 of the Bird v Cat article

Yet for all their indefatigable stalking, cats will rarely take on the most cursed vermin in our midst. “The myth has been propagated that urban roaming cats do a lot to control the rat population,” Mr. Schroeder said. “But science has shown that cats don’t predate on rats, especially not the rather large variety seen in our cities.”

Cats’ toll on birds is a less mythical matter. In one famous study reported in the journal Nature, Kevin R. Crooks of the University of California, Santa Cruz, and Michael E. Soulé of the Wildlands Project in Colorado looked at the population dynamics among cats, coyotes and scrub birds in 28 “urban habitat fragments” of Southern California. In the developments to which coyotes had access, free-ranging cats were rare and avian diversity high. The coyotes ate cats but rarely bothered with birds. Where coyotes were excluded, cats ranged free and bird diversity dropped.

Very likely, the cats got the young. As it happens, many temperate-zone birds go through a dangerous time early in life, when they are too big for the nest but still poor at flying. The fledglings spend their time on the ground, hiding in bushes and waiting for their parents to come feed them. People come upon the baby birds and think, poor dear, it’s fallen from its nest, but no, this is the system. “They’re incredibly vulnerable,” Dr. Marra said, “and in high-cat densities, the fledglings get nailed.”

In a newly completed study, Dr. Marra and his students used radio transmitters to track fledgling survival in two Washington suburbs: Bethesda and my own Takoma Park. The towns are similar socioeconomically and demographically, but while much of Takoma Park is crawling with outdoor cats, many streetscapes in Bethesda are, for reasons that remain unclear, largely cat-free. At least partly as a result of this discrepancy, Dr. Marra said, fledgling survivorship among Bethesda birds is about 55 percent, similar to what you would see in a natural population. But for birds that happen to be born in my tree-lined paradisiacal hamlet, only 10 percent last long enough to take wing.

There are ways to keep a cat happy inside. Becky Robinson, the founder and president of Alley Cat Allies, who has taken in five strays, recommends any number of the increasingly popular “exclosures,” plastic pods that you pop into your window for the cat to enter and watch the world, or snaky mesh cages that you can even take camping.

I’m relieved to report that our new cat, Manny Jr., is content with our screened-in porch and the many hunting opportunities our home affords. Sorry, but the crickets are fair game.

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