NORTHEASTERN NATURALIST2001 8(1):51-62
POPULATION TRENDS OF WINTERING BATS
IN VERMONT
STEPHEN C. TROMBULAK 1, PHILIP E. HIGUERA 1,2, AND MARK DESMEULES 3
ABSTRACT - We report the results of all readily available inventories of
wintering bats in Vermont. Surveys at 23 hibernacula were compiled from the
literature and unpublished data of numerous biologists and cavers. The earliest
Vermont records date back to 1934. Only five hibernacula were systematically
surveyed for more than 45 years. Despite data limitations, several trends have
emerged. Since the 1930s, wintering populations of Myotis sodalis have dramati-
cally declined; wintering populations of M. lucifugus have increased; and winter-
ing populations of all other Vermont species (M. leibii, M. septentrionalis,
Eptesicus fuscus, and Pipistrellus subflavus) have remained small.
INTRODUCTION
Numerous studies have shown that populations of several species of
North American bats have declined in recent decades (Hill and Smith
1984, Humphrey 1978, Pierson 1998, Tuttle 1979). Currently, six spe-
cies are listed as endangered by the U.S. Fish and Wildlife Service. In
Vermont, these species include the federally endangered Indiana bat
(Myotis sodalis Miller and Allen) and the Vermont state threatened
small-footed bat (M. leibii Audubon and Bachman). Many species of
bats whose populations were considered secure have shown recent
population declines (Pierson 1998). For other species, current informa-
tion is insufficient to assess trends in their population sizes.
Factors contributing to bat population declines (generally reviewed
in Hill and Smith [1984] and Altringham [1996]) include pesticide
poisoning (Geluso et al. 1976, Reidinger 1976, Tuttle 1979), chemical
pollution (Tuttle 1979), siltation of waterways (Tuttle 1979), flooding
(Hall 1962), deforestation (Tuttle 1979), disturbance by biologists and
caving enthusiasts (Humphrey 1978, Speakman et al. 1991), and human
interference (Fenton 1970, Tuttle 1979). The foremost factor leading to
population declines is the wanton destruction of roost sites, particularly
hibernacula (Humphrey 1978, Sheffield et al. 1992). Thus, North
American bat conservation efforts have focused largely on protection of
hibernacula from vandalism and physical alterations.
Eighteen of the 45 bat species present in North American rely sub-
stantially on caves or abandoned mines for roosting sites. Thirteen use
1 Department of Biology, Middlebury College, Middlebury, VT 05753.
trombulak@middlebury.edu; 2 Present address: College of Forest Resources, Box
352100, University of Washington, Seattle, WA 98195; 3 The Vermont Nature
Conservancy, 27 State Street, Montpelier, VT 05602; Present address: Box 266
Route 194, Alna, ME 04535.

Northeastern Naturalist Vol. 8, No. 152
caves and mines year-round for both reproduction and winter roosts,
while the remaining five use them exclusively for hibernation (Barbour
and Davis 1969). Bats choose suitable hibernacula based on tempera-
ture, humidity, air circulation, and morphology of the cave or mine
(Hitchcock 1949, Raesly and Gates 1987, Twente 1955). The range of
acceptable conditions is typically narrow. Thus, desirable caves and
mines are relatively rare but essential to the survival of a population.
Because of their dependence on caves and mines for hibernation, inven-
tories of bats at hibernacula provide a useful index to population trends
over time. These indices can aid in the status assessment of bat species
within a defined geographic area.
In addition to M. sodalis and M. leibii, four other bat species hiber-
nate in Vermont: M. lucifugus Le Conte (little brown bat), M.
septentrionalis Trouessart (northern long-eared bat, = M. keenii
septentrionalis), Eptesicus fuscus Palisot de Beauvois (big brown bat),
and Pipistrellus subflavus F. Cuvier (eastern pipistrelle). Unpublished
research on cave bats in Vermont dates back to 1913; however, the
earliest documented inventories did not begin until 1934 (Fichtel 1992).
We report the results of all available inventories of wintering bats in
Vermont. This information may facilitate a better understanding of
trends in wintering bat populations in Vermont and assist in efforts to
promote their conservation.
METHODS
A thorough search of the literature, state agency records, and unpub-
lished data of biologists and cavers who have studied bats in Vermont
was performed to obtain information on wintering population sizes.
Banding and census data from October to April (1934-1999) were
gathered from the following sources: (1) Harold Hitchcock’s personal
field notebooks from Middlebury College’s Starr Library Archives
(Middlebury, Vermont); (2) Donald Griffin’s personal Vermont field
notebooks from Middlebury College’s Starr Library Archives; (3) Grif-
fin (1940a); (4) Griffin (1945); (5) Davis and Hitchcock (1965); (6)
Records from the Nongame and Natural Heritage Program, Vermont
Fish and Wildlife Department, 103 South Main Street, Waterbury, Ver-
mont 05471-0501; (7) Fichtel (1992); (8) Data from Marc DesMeules
not available from Source 6; (9) Data from Alan Hicks (New York State
Department of Environmental Conservation) not available from Source
6; and (10) Data from William Kilpatrick (Department of Biology,
University of Vermont) not available from Source 6. The Vermont
Nongame and Natural Heritage Program (Source 6) is a repository for
field notes from bat researchers in Vermont, particularly Chris Fichtel
(Vermont Nongame and Natural Heritage Program and the Vermont
Nature Conservancy), William Kilpatrick, Kevin O’Classen (Vermont
Cavers Association), Steve Parren (Vermont Nongame and Natural
Heritage Program), and Stephen Trombulak.