Geography Reference
In-Depth Information
a steady diet of insects. Residents also supplement the diverse urban forest
with generous of erings of birdseed.
Our discovery of subirdia in Seattle is not unique. Throughout Britain, in
deciduous woodlands of California and Ohio, grasslands of Arizona, forests
of Japan, and shrublands of Australia moderate levels of urbanization also
provide an abundance of various resources that increases the number of bird
species beyond that found in either wilder or more densely populated set-
tings. However, this is not always the case. The peak in bird diversity occurs
where the creative hand of urbanization surpasses the destructive hand. In
temperate locales, the creation of habitat diversity allows more birds to colo-
nize suburbs than are extinguished by the destruction of unique habitats re-
quired by shy and intolerant species. In tropical settings, where magnii cent
rainforests rife with birds are converted to suburbs, bird diversity drops. And
it plummets as one moves ever closer to the tropical city's center.
I awoke on my i rst morning in Alajuela, Costa Rica, to the noise of motor-
bikes and parrots. I bolted from bed to i nd scattered pairs of crimson-fronted
parakeets perched among the trees, electrical wires, and buildings. Like foot-
long emerald ornaments with pointed tails, red freckles, and golden under-
wings, the birds decorated the central plaza. They wheeled about, grooming
each other and mixing freely with street pigeons. Such tropical cities hold
avian riches, but their splendor is deceiving. Jef Norris knows this deception.
He earned his Ph.D. by counting birds along six separate urban-to-wildland
gradients in Central America. These gradients each included the full range of
developments that occur between a city and a nearby forest reserve, such as a
national park. Jef discovered on both the Atlantic and Pacii c sides of Costa
Rica that bird diversity peaks along the edges and deep into the forest re-
serves that compose nearly 30 percent of this Central American nation. He
counted up to 116 species in the forest, but no more than 53 in the suburbs.
Counts of 20 to 30 bird species were more typical of the city center. Other
scientists have found similar results in tropical Mexico, Ecuador, and Singa-
