Scampering through the Chesapeake marshland is a bird that doesn't want to be found, and may be disappearing: the black rail.

The little rail is the size of a sparrow, with an auburn smudge on the back of its neck and shocking red eyes. It likes to walk, not fly, moving unseen through tunnels in thick mats of grass. It ventures out, if at all, between midnight and dawn.

Sometimes the black rail announces itself with a stammering, high-pitched call. Sometimes it doesn't.

These secretive habits may protect the bird from predators, but they also helped to mask the dramatic decline of what researchers say may be the most endangered bird on the Atlantic Coast.

Black rails have been declining slowly throughout their Eastern range, which historically spreads from Connecticut to Florida. Now, the Center for Conservation Biology of the College of William and Mary / Virginia Commonwealth University reports that the loss has picked up speed.

According to the center's 2009 report, black rails in the Chesapeake region alone have declined more than 75 percent in the last 10-20 years. The number of breeding sites has dropped 80-85 percent.

"This recent decline has been more dramatic than the historic change, with a rapid loss in the number of breeding sites and numbers of birds," said senior biologist Michael Wilson.

Although the birds are under-studied, available data indicate that Maryland, Virginia and North Carolina are their remaining stronghold. Even there, the population has crashed.

"All three states have had precipitous declines, particularly over the last 10-15 years," Wilson said. "It would cut a big hole from their stronghold if we were to lose the population in the Chesapeake."

Wilson said the need for action is critical.

"Without it, the black rail could be extinct from Maryland and Virginia in our lifetimes," Wilson said.

In Virginia, the center found black rails at only 12 of 328 places where they were previously known to exist. All of these sites were in the Bayside marshes of Accomack County on the Delmarva Peninsula. The center found no black rails on Virginia's Western Shore, including the James, York and Nansemond rivers.

The Maryland Department of Natural Resources has also documented the decline. A study of black rails in the early 1990s found no immediate problems, but a follow-up study in 2006 raised alarm.

"We lost rails at 85 percent of the points we studied," said regional ecologist David Brinker. "You don't need a lot more statistics for that to be a cause of concern."

More research is needed to pinpoint the cause. Scientists know that land use, climate change and natural predators disturb the black rail's shelter and nesting sites. They don't know which of these factors, if any, plays a leading role.

Black rails depend on the highest elevation of marshland where the ground feels wet, but not flooded. The high marsh is a transition zone to inland areas, existing beside farm fields, forests and developed areas.

Anything troublesome in the neighboring environments - from polluted stormwater runoff to hungry foxes and raccoons - reaches the high marsh first. The high marsh is also the zone most likely to be drained for other uses, or ditched for mosquito control.

However, black rails have vanished from high marsh habitat where there is no obvious sign of disturbance.

"It may not be that habitat is the problem, but some function of the habitat," Wilson said. "When a species doesn't occupy all of its available habitat, the problem may be something in the habitat that we're not measuring yet."

The impacts of climate change are one possibility. The rising sea level could drive saltier water deeper into Chesapeake marshes, threatening sensitive vegetation and wildlife.

Sea level rise could also turn the relatively dry high marsh into a watery plain. Ideally, the whole system would shift inland and the high marsh would establish itself again. In many places, though, high marsh sits next to developed land and has nowhere to go.

Black rails and other species that use the high marsh exclusively are most vulnerable.

"We'll lose and gain marsh, but we'll lose high marsh the most as it turns into low marsh," Wilson said. "Eighty to 90 percent of the high marsh could be lost even though the overall loss wouldn't be that high. It's like a complete state change for marshes in the Chesapeake Bay area."

Black rails migrate south of the Bay for the winter. Problems may exist in the winter habitat that compound the loss every year.

"It could be that we're not doing anything wrong in Maryland, but they go down to Florida and the Gulf Coast and encounter a problem there," said Brinker. "It's a gigantic puzzle that we have to work on very quickly."

The Center for Conservation Biology is coordinating a partnership between 19 universities, government agencies and conservation organizations to improve research on the black rail and raise awareness of its status.

Wilson thinks their work may eventually lead to federal-level protection. The black rail is on Maryland's endangered species list but has no protective status in Virginia.

"It's amazing that this bird has not received the same attention given to other species that are also declining but more numerous," Wilson said. "For some reason, the black rail has always just been in the background."