Nine species of bats are considered regular residents of New Jersey. These include the little brown bat, big brown bat, northern long-eared bat, small-footed myotis, Eastern pipistrel, Indiana bat (state and federally endangered), hoary bat, red bat and silver-haired bat.
The hoary, red and silver-haired bats are part-time residents that are found here from spring through fall when they migrate to southern states for the winter. The other six species remain here throughout the entire year and require special habitats for winter hibernation.
Natural caves once provided hibernating habitat for bats, but today most caves are subject to disturbance by people and thus are not suitable for use by bats. Abandoned mines and tunnels have replaced natural caves as the primary winter habitat for bats in many parts of the country because they are often unsafe to enter or inaccessible to people.
New Jersey's largest known bat hibernaculum is the Hibernia Mine in Rockaway Township, Morris County. The mine was abandoned in the early 1900s and the first record of bats using the mine is from the 1930s. In the decades that followed, the mine continued to provide winter habitat for bats but frequent and constant human disturbance limited the mine's potential.
Unsuccessful attempts were made by landowners to keep people out of the mine, but these efforts also made it unavailable to the bats. During the summer of 1994, the Endangered and Nongame Species Program negotiated an agreement with landowners to install a special bat conservation gate to keep people out but allow free access by the bats.
The state has also acquired the property through the Green Acres Program and it is currently part of the Wildcat Ridge Wildlife Management Area and is listed as a Watchable Wildlife Site.
The ENSP conducts a biennial winter survey to assess the bat population in the Hibernia Mine. A 1999 survey found a peak of more than 30,000 bats.
Starting in 2003, a Summer Bat Count has been done to map summer roosting locations throughout New Jersey.
New hibernacula have been located and protected including a tunnel in Worthington State Forest in Warren County.
Cooperating with the ENSP on these efforts are the Division of Parks and Forestry, the US Army Corps of Engineers, the US Fish and Wildlife Service and Bat Conservation International.