But now comes a surprise. When students went to downtown Seattle to count bird species, within the first 10 to 15 minutes they spotted pigeons, finches, sparrows, crows and an occasional hummingbird.
Their count was 10 to 15 different kinds of birds — not many, but they expected that.
When they went the other way (to the far edge of the metropolitan area near the Cascade Mountains, where there is mostly forest, protected parks, reservoirs, and humans are sparse), in the first 10 to 15 minutes, they found a very different set of birds (woodpeckers, wrens, warblers, chickadees).
In all, 20 different species — more, but not many more than downtown.
Then they went to the in-between zone, the Seattle suburbs, where they expected an in-between count, something like 12 different kinds of birds. But that’s not what happened.
Birds in the suburbs.
“We were astonished,”
Marzluff writes. The suburban count (again in the first 10 minutes) was “30 or more species,” says Marzluff, some from downtown, some from the mountains, but also spectacularly new samples of “violet-green swallows, willow flycatchers, killdeer, orange crowned warblers, American goldfinches, and Bewick’s wrens … [plus a few] white crowned sparrows.”
The suburbs produced, by far, the most biologically diverse collection of birds.
What? This region that’s all sprawl, a hodgepodge of strip malls, yards, highways, parking lots, hedges, fences, is “a mecca for birds”? More than a forest? No way, thought Marzluff. So he counted again. Then again.
And after checking and compiling “more than 100 locations in and around Seattle,” he writes, he and his team discovered “a consistent, but unexpected relationship between the intensity of development and bird diversity.”
To his great surprise, Marzluff concluded that the “greatest diversity was not in the most forested setting. Instead, bird diversity rose quickly from the city center to the suburbs and then dropped again in the extensive forest that eases Seattle into the high Cascades.”
If you plotted it on a graph, bird biodiversity looks like this …