One of the region’s more elusive mammals, the New England cottontail, is alive and apparently well at the Connecticut Audubon Society’s Roy and Margot Larsen Wildlife Sanctuary in Fairfield.

According to the Audubon, more than 80 percent of the region’s New England cottontails have vanished in recent decades and the remaining population is being considered for listing under the Endangered Species Act. The Larsen Sanctuary is one of the few locations in Fairfield County with a confirmed population of the rabbits.

When he was a student at the University of Connecticut, in 1969, Milan Bull, now the Audubon’s senior director of science and conservation, trapped and released New England cottontails at Larsen as part of a college research project. In 2007, state wildlife biologists confirmed that they were still there.

Then last month, a state Department of Energy and Environmental Protection survey from the winter of 2014-15 showed that New England cottontails continued to live within the thickets and briar patches of the Larsen Sanctuary.

New England cottontails are indistinguishable in the field from their close relatives, the much more common eastern cottontail, which is not native to Connecticut, so DNA tests are needed to confirm their presence. Biologists wait until there is snow on the ground and then collect rabbit droppings. Travis Goode of the DEEP said 12 samples were collected at Larsen last winter. Five were from New England cottontails and seven from eastern cottontails.

In general, a good cottontail habitat — thickets of briars and other shrubs — will support one to two rabbits per acre, half New England cottontails and half eastern cottontails. The 155 acres of the Larsen sanctuary has about eight to 10 acres of rabbit habitat.

New England cottontail populations have fallen for the same reasons as so many other species — habitat degradation and fragmentation. The scrub-shrub growth that the rabbits need has given way to forests and lawns; housing developments, strip malls, and highways have prevented rabbits in one patch from mating with rabbits in another. Some of the region’s fastest-declining songbirds, including blue-winged warblers and chestnut-sided warblers, need the same habitat as New England cottontails.

The situation is less dire for eastern cottontails, which do just fine in suburban landscapes.