CONCORD, N.H. – More than 50 years ago, New England Cottontail rabbits were plentiful from New Hampshire’s Lakes Region to the Seacoast.

Today, wildlife biologists believe there are fewer than 100 of the small brown rabbits in a state that has seen the sharpest declines in New England.

Biologists blame the loss of habitat — patches of thickets in younger forests — and they’re working across the region to create a hospitable environment the rabbits.

“They’re the poster child for the loss of shrubland habitat,” said Steven Fuller, a wildlife biologist with the New Hampshire Fish and Game Department.

Last year, New Hampshire, Massachusetts and Connecticut received federal grants to help preserve the cottontail.

Since then, teams of state and federal agencies have been stepping up efforts locally and are working together in the New England region to control and create new habitat for the rabbits.

The Rangewide New England Cottontail Initiative is focusing on areas targeted for conservation and restoration on public and private land with plans to branch out to Rhode Island, New York and Maine.

New Hampshire and Maine — another state with a dramatic decline in the New England Cottontail — are working with the National Fish and Wildlife Foundation on separate restoration projects.

Tony Tur, an endangered species biologist with the U.S. Fish and Wildlife Service, said new forests formed on farms that were abandoned in New Hampshire from the 1900s through the 1930s, which appealed to the cottontails.

But as forests grew older and more dense, the thickets preferred by the rabbits began to disappear, and remaining pockets have been fragmented by development. The New England Cottontail also was competing for habitat with another rabbit, the Eastern Cottontail, which is better at adapting to different habitats.

The recent expansion of the Portland International Jetport in Maine is an example of how the cottontail’s preferred habitat of brush and brambles is being eliminated.

Because of Federal Aviation Administration concerns, cottontails were removed from 13 acres to keep wildlife away from the runways, said Wally Jakubas, mammal group leader and wildlife biologist with the Maine Department of Inland Fisheries and Wildlife.

Biologists were surprised to find 15 New England Cottontails, which were captured and relocated. The last survey conducted in Maine indicated there were only 300 of the rabbits in the state.

As recently as 1960, cottontails were found east of the Hudson River in New York, across Connecticut, Rhode Island and Massachusetts, and in southern Vermont, New Hampshire and southern Maine, the U.S. Fish and Wildlife Service says.

These days, they’re considered extinct in Vermont, where there hasn’t been a sighting since 1971.

Four years ago, the U.S. Fish and Wildlife Service chose not to pursue protection under the Endangered Species Act. But they’ve been declared endangered by the states of Maine and New Hampshire, where officials are working with a small group of landowners to volunteer to set aside areas dedicated to the animals.

In New Hampshire, one of them is the Audubon Society of New Hampshire, which plans in August to convert two 5-acre forest plots at the Bellamy River Wildlife Sanctuary in Dover into cottontail habitat.

The goal is to plant a mix of native seeds to create a shrubland habitat, said Phil Brown, director of land management.