Robert Krulwich, NPR

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…