Global warming a threat to salt-marsh sparrow in Va.

One of an occasional series

The salt-marsh sparrow is Virginia's polar bear.

The huge white bear and the little brown bird are both threatened by global warming.

And what happens to them, scientists say, could say a lot about what happens to us.

The bears, which have gotten all the publicity, are in trouble because the Arctic sea ice they spend a lot of time on is melting.

The sparrows may be in worse shape. They spend their entire lives in salt marshes -- ecologically valuable wetlands that are being destroyed by rising seas caused by a warming planet.

"It's a complete prisoner to the salt marsh," said Bryan Watts, director of the Center for Conservation Biology at the College of William and Mary and Virginia Commonwealth University. "If we lose the salt marshes, we lose them."

While scientists have studied polar bears for years, not a lot is known about the salt-marsh sparrow.

To help rectify that, Watts and other scientists gathered this spring along a marsh at the southern tip of the Eastern Shore, in the Eastern Shore of Virginia National Wildlife Refuge.

They planned to count sparrows to determine the bird's population -- important data in documenting the bird's expected decline.

In an age of high-tech science, this group was distinctly old-school. They planned to pull a 200-foot nylon rope, weighted with rock-filled plastic jugs, through the ankleand calf-high marsh grasses to flush the birds toward vertical nets.

"Rope, start dragging!" hollered Fletcher Smith, a burly, red-haired conservation-center biologist who led the day's effort. "If you see something flush, yell."

The marsh was muddy but surprisingly firm under foot. The scientists trod past mussel shells and scattering fiddler crabs.

It was a gorgeous, azure-sky morning. Just beyond the marsh lay a blue lagoon, then some islands, and beyond them the Atlantic Ocean. Egrets, ospreys and eagles flew by.

As sparrows sprung from the grasses in low flight, the crew herded them toward the fine-mesh "mist" net -- so named because it is barely visible. The birds got tangled in the net.

After carefully extracting the birds, Smith and a helper measured and weighed them and put bands on their legs. Finding banded sparrows in the future might reveal something about their movements.

In Watts' hand, a salt-marsh sparrow struggled at first then quickly calmed down. The bird was handsome, with a dark cap, an auburn stripe through its eye and a brown back.

But if salt-marsh sparrows died out, so what?

They play a role in nature by eating insects and helping spread the seeds of marsh grasses, Watts said.

Beyond that, he added, "There's some responsibility for us to maintain these species that are vulnerable to our activities."

Salt marshes are important homes not just to sparrows but to young fish and crabs that people like to eat.

Scientists expect salt marshes to decline significantly either because rising seas drown them, or because roads and structures block them from moving naturally inland as the waters rise.

Some small, marshy islands are disappearing now, Watts said.

The sea level in southeastern Virginia rose about a foot in the past century -- the highest rate on the East Coast. Scientists project the sea to rise 2 to 7 feet by 2100, as the effects of global warming worsen.

That would be a huge change, threatening not just sparrows but waterfront homes, businesses and military bases.

The seas are rising in part because warm water expands. In Virginia, the natural sinking of coastal land contributes to the problem.

"Sea-level rise isn't just going to be an issue for these birds," Watts said. "It's going to be an issue for other species, including us."

Contact Rex Springston at (804) 649-6453 or rspringston@timesdispatch.com.