The lack of influence of park vegetation is even clearer when the researchers examined bird abundance (the total number of birds seen, regardless of species), with summer bird abundance actually being consistently lower where tree abundance is higher.
The lack of correlation between trees and the bird populations is important, Kinzig notes, because the variety and number of trees planted are among the few significant variables present in the make-up of the parks themselves, and could be affected by economic factors. Tree landscaping is done by the city, and could conceivably be influenced by the neighborhood's age and economic status.
Though the study eliminates park landscaping as a factor, it does not yet pinpoint specific explanations for how neighborhood economic status could affect bird populations.
"Something that happens in the radius of 200 meters from the park boundaries is influencing the diversity of birds," Kinzig noted. "Whatever people are doing is having an influence, because we can't explain it with the park itself. There's a variety of things it could be what people are planting, it could be socio-economic differences in how often you feed birds, maybe the rich people have more bird feeders...
"It could be something as small as the feral and domestic cats and other predators that live in the neighborhoods not just how many people have cats, but how many of them are prowling around wild and are good at catching birds, or whether or not people put bells on their necks... Or it could be zoning; what the city plants on the median strips; or how much industrial and commercial activity is allowed," she said. "We don't know, but it's something about the differences in people's lifestyle."
Though the mystery is hard to unravel, there are still some ecological factors that Kinzig thinks could be relevant.
"We still want to l
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Contact: James Hathaway
Hathaway@asu.edu
480-965-4823
Arizona State University
8-Aug-2002