Blackwater National Wildlife Refuge, already vast at 27,000 acres, is becoming even larger.

The U.S Fish and Wildlife Service announced Thursday that it has acquired 410 acres of new land for the refuge on Maryland’s Eastern Shore from The Nature Conservancy.

The expansion will provide more protected habitat for birds and help the refuge cope with the Chesapeake Bay’s rising waters, which are already killing trees and inundating areas of tidal marsh. The changes are visible even from the roads around the refuge, where dead and leafless trees once on solid ground now stand in brackish water. The refuge contains one-third of Maryland’s tidal wetlands, and it is internationally recognized as crucial bird habitat, particularly for migratory waterfowl.

The Conservancy bought one tract in 1993 to protect Blackwater’s many bird species, including the largest population of bald eagles on the East Coast. The group acquired the second tract, which was largely farmland, in 2007, after neighbors approached the group because they were worried about development.

“The acquisitions contribute to the mosaic of lands already protected by other partners, ensuring that landscapes are connected and functional,” said Marcia Pradines, manager for the Chesapeake Marshlands National Wildlife Refuge Complex, in a news release.

One tract features wetlands that are currently building elevation on pace with the local rate of sea-level rise, according to the Conservancy. The other is upland that helps buffer against flooding and gives the marsh room to migrate inland in response to encroaching water.

The properties adjoin the Nanticoke River, just east of the refuge in Wicomico and Dorchester County. The Nanticoke remains one of the state’s most pristine rivers, with returning populations of yellow perch and newly discovered sturgeon. But it is also an area of concern for conservationists because of increasing industrial agricultural land use in the area.

The funds for the purchases came from the Migratory Bird Conservation Commission, some of which was raised through the sale of federal “duck stamps.”