2 
PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES 
Series 4, Volume 65, Supplement I 
In 1994, the federal government designated 24 species or subspecies of bats in the 
United States (U.S.) and its territories as Category 2 candidates for listing as Endan¬ 
gered or Threatened under the U.S. Endangered Species Act. Category 2 was elimi¬ 
nated in 1996, but taxa previously receiving this designation were informally consid¬ 
ered “species of concern.” Various state and federal agencies and conservation 
organizations subsequently assigned bat species of concern to more formal conser¬ 
vation categories. Some of the original 24 taxa designated as Category 2 candidates 
in 1994 were later listed as Endangered, whereas others were subject to refinements 
in knowledge of their taxonomy and distribution. The remaining 20 species of bats 
have been the subjects of increased research efforts over the past two decades, and 
are the focus of this review. Two species occur in the U.S. Territories. All of the 18 
mainland species ranges include areas west of the Mississippi River (15 are found 
primarily in western states), and 13 occur in California (72% of the 18 mainland 
species). In this review, we provide a comprehensive summary of the literature per¬ 
tinent to the conservation designations, systematics, distribution, habitats, relative 
abundance, foraging, diet, roosting ecology, population ecology, and management of 
each of these 20 species. The species of concern are distributed among four families 
of bats. The Samoan flying fox ( Pteropus samoensis) belongs to the Old-World fam¬ 
ily, Pteropodidae. The California leaf-nosed bat ( Macrotus californicus ), red fruit bat 
(Stenoderma rufum), and Mexican long-tongued bat ( Choeronycteris mexicana ) are 
members of the New World family, Phyllostomidae. Three species belong to the cos¬ 
mopolitan family Molossidae: the greater bonneted bat ( Eumops perotis californi¬ 
cus ), Underwood’s bonneted bat ( Eumops underwood!), and the big free-tailed bat 
(Nyctinomops macrotis). Most bat species of concern are in the globally distributed 
family Vespertilionidae: Townsend’s big-eared bat ( Corynorhinus townsendii), 
Rafinesque’s big-eared bat (C. rafinesquii ), spotted bat ( Euderma maculatum), 
Allen’s big-eared bat ( Idionycteris phyllotis), southeastern myotis ( Myotis austrori- 
parius ), western small-footed myotis (M ciliolabrum ), long-eared myotis (M evotis ), 
eastern small-footed myotis (M. leibii ), Arizona myotis (M occultus ), fringed myotis 
(M. thysanodes ), cave myotis (M. velifer), long-legged myotis (M volans), and Yuma 
myotis (M. yumanensis). An impressive amount of knowledge has accumulated about 
these species since their informal designation as species of concern, but this knowl¬ 
edge is unevenly distributed. Comparatively little research has been conducted on 
the Samoan flying fox and the red fruit bat over the past decade in tropical territo¬ 
ries, nor on the Mexican long-tongued bat and Underwood’s bonneted bat in the 
southwestern U.S. Within temperate regions of the U.S., habitat use of two eastern 
species that roost in hollow trees or caves (southeastern myotis and Rafinesque’s big- 
eared bat) has been the focus of much research, as have aspects of the biology of 
cave-roosting and tree-roosting western species, particularly where information 
about management of forests, caves, and abandoned mines can be used to benefit bat 
conservation. Comparatively less information has accrued about species that roost 
in rock crevices and high on cliff faces. Other major gaps in information are also 
identified. We anticipate that this review will help guide future research and conser¬ 
vation efforts directed at the bat species of concern. 
Keywords: Bats, Chiroptera, Choeronycteris, Conservation, Corynorhinus, Ecology, 
Eumops, Idionycteris, Macrotus, Myotis, Nyctinomops, Pteropus, Stenoderma. 
In her landmark early publication on the bats of California, Hilda Grinnell (1918) made note 
of the desirability to protect and conserve bat populations throughout the United States (U.S.) and 
cited conservation efforts that extended back to the early 1800s. Mounting concern for the conser¬ 
vation of bat populations in the U.S. and territories has been expressed repeatedly in other techni¬ 
cal publications since at least the middle of the last century (for example, Mohr, 1952, 1972; 
Manville, 1962; Barbour and Davis, 1969; Cockrum, 1969,1970). The Indiana bat {Myotis sodalis) 
