Spreading suburbs lure birds of a different feather

A killdeer picks its way along the beauty bark in the landscaping strip that wraps this stormwater-management pond, so new it still bears the ridges of bulldozer tracks. Mallards flap up from the landscaping fabric.

They are brave colonizers of a new environment that was a forest just last year. Across Puget Sound, landscapes are being transformed by development, and bird populations are changing along with them, University of Washington researchers have learned.

By tracking 27 research plots on the suburban fringe of King and Snohomish counties over eight years, researchers found development brings not necessarily extinction but replacement, with new native species colonizing the suburban environments that used to be forests.

Researchers did something no one in this region has done before: They looked not only at local bird populations, but also at which birds were surviving and reproducing over time, leading to a change in the structure of the local bird community.

"It's a change in who's top," said biologist John Marzluff, who led the study.

In more places, he sees more birds of the edge and the open — juncos were booming in his research plots — while birds that take cover in thickets of native understory and forest canopy, such as winter wrens and Swainson's thrushes, were in decline. "The habitat changed," Marzluff said. "The birds can tell the story."

The researchers followed plots in three types of landscapes: five forest reserves, nine developed subdivisions and 13 changing landscapes — "Scrapervilles," as they came to call the sites where forests were replaced with developments usually named for the ecosystems and animals that used to be there.

Take Beaver Lake Estates on the Sammamish Plateau — or "Beaver Cleaver," as researchers dubbed it, after developers slicked off the trees in a parcel under development.

Nail guns and bulldozers were the soundtrack when researcher M. David Oleyar checked his plots this year. He and Marzluff tallied which birds were in the plots and tracked breeding success. That's when they spotted shorebirds and waterfowl in a stormwater pond where they had logged forest birds the year before.

Even juncos couldn't hack it in some developments, where homes were crowded densely and planted with lawns and nonnative landscaping. A concrete pumper purred in the background, laying the foundations for the next group of houses at Cougar Crest in Bellevue.

"This is a local nuke site, a small volcanic eruption; there just isn't much left here," Marzluff said. "The houses are so close together there isn't even any artificial habitat to speak of."

But in other developments, even narrow greenbelts made a big difference, and older developments, with mature trees, were thronged with birds.

Unexpected lesson

The lesson, Marzluff decided, wasn't what he expected. It wasn't "Don't develop" but rather "Don't do the same thing everywhere."

Researchers found that the amount of habitat and what was in it — a variety of snags, understory, canopy, mature trees and open areas — was more important than its shape. Connected swaths of habitat didn't matter as much for birds, a highly mobile species, as for other animals such as amphibians.

Even small things every homeowner can do in suburban developments help birds, researchers found. Consider Montare, a subdivision north of Woodinville, where native songbirds did both well and badly, depending on how residents managed their little slice of the world.

On a walking tour, the enemy was quickly outed: that suburban icon, the lawn.

Some homes had lawns as sharply edged as a rug, and the turf glowed a hyper-fertilized green. Those lawns offered little to eat and nowhere to hide and were virtual bird-free zones. But nearby, the development's greenbelt was hopping.

The discarded legs of a rabbit, dropped by a Cooper's hawk, littered a trail through the greenbelt. When Marzluff put up a mist net to briefly trap songbirds for banding, in no time he found himself mano-a-mano with a spotted towhee. When he played the call of a Bewick's wren on a loudspeaker, its namesake leapt from the tangled understory and stood at rapt attention.

A snag of a dead tree was densely drilled with woodpecker holes, and the morning was alive with the sound of birdcalls.

But Marzluff saw trouble, too: the white flags of an invisible dog fence encroaching on the greenbelt. Stacked nearby was a heap of branches cleared from native understory for the fence. Invasive ornamental ground cover smothered a hillside. And a backyard pool project was intruding on the spot where a Swainson's thrush had returned to nest for years.

This spot is among the so-called walking dead: The bird will keep coming back here because it is site-faithful. But once it dies, no other Swainson's will nest here. It's become a dead zone for that species.

A critical time

Across Washington, populations of some common native songbirds are in decline. Evening grosbeak populations are down 97 percent over the past 40 years, and purple finches are down 87 percent. Yellow-headed blackbirds have declined 72 percent and Western meadowlarks 60 percent, according to Seattle Audubon.

Marzluff sees a region at a tipping point. More Scrapervilles, more messing with what habitat is left, and bird populations will suffer. "Future losses [of birds] will be much greater," Marzluff said, "depending on how we develop."

Lynda V. Mapes: 206-464-2736 or lmapes@seattletimes.com