O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
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available report on roosting of California leaf-nosed bats published during 2007-2016. Two species 
limited in distribution to Arizona or Arizona and New Mexico (Underwood’s bonneted bat and 
Mexican long-tongued bat) were the subjects of only one paper about roosting over the last 10 
years. 
Radio telemetry has played a key role in gaining knowledge about roosting habits of species 
of concern. The number of individual bats radio tracked among the various species of concern mir¬ 
rors this general increase in knowledge, with most applications involving three species of forest 
bats. Based on papers reviewed in the species accounts, we estimate that the following number of 
individuals have been radio tagged to determine roost locations (and to a lesser extent foraging 
habits): more than 310 long-legged myotis, more than 290 Rafmesque’s big-eared bats, and more 
than 200 long-eared myotis. Minimum number of bats radio tagged range from 30 to 100 for five 
species: fringed myotis, Arizona myotis, Townsend’s big-eared bat, spotted bat, and red fruit bat 
(in descending order). From 10 to 30 individuals were tagged in studies of western small-footed 
myotis, eastern small-footed myotis, Yuma myotis, Allen’s big-eared bat, and the big-free tailed 
bat. From three to seven individuals were tagged in tracking studies of southeastern myotis, 
Samoan flying fox, Underwood’s bonneted bat, and the greater bonneted bat. We found no recent 
published or publicly accessible papers available on radio tracking of the California leaf-nosed bat, 
the cave myotis, or the Mexican long-tongued bat. 
Most of the telemetry-based roosting studies concentrated on adult females during summer, 
with the objective of understanding roost use for birthing and rearing young. During the summer 
maternity season, females of the U.S. species of bats that spend the warmer seasons in trees usual¬ 
ly roost in basal hollows, cracks, cavities, or under bark in relatively small groups, and they change 
roosting trees on average every one to three days (well demonstrated for Rafinesque’s big-eared 
bats, long-eared myotis, fringed myotis, and long-legged myotis). The three species of Myotis that 
are in this group also frequently roost in rock crevices, where they also switch roosts at a similar 
frequency, as do Arizona myotis using trees as roosts. Colonies tend to use many different roosts 
within a core area that will vary by species. The high frequencies of roost switching are character¬ 
istic of the fission-fusion social systems of many bats, and result in group sizes that vary greatly. 
In the case of the above species roosting in trees or rock crevices, maternity group sizes are typi¬ 
cally small but will vary from day to day and among study areas. Some typical group sizes and 
maxima when roosting in trees are: Rafinesque’s big-eared bats (six to 40; 100), Allen’s big-eared 
bat (two to 13; 21), long-eared myotis (one to four; 14), fringed myotis (one to 35; 118), long- 
legged myotis (two to 50; 459), and Arizona myotis (one to 180; 500). Where studied, males of 
these species tend to roost solitarily but also change roosts frequently. 
Roost switching is less well-known for species of concern that do not commonly roost in trees. 
High frequencies (every one to two days) of roost switching also characterize the eastern and west¬ 
ern small-footed myotis that roost under rocks, in talus, or in soil crevices during summer. Group 
sizes in both of the latter species are small (ranging one to 20, typically less than five) during sum¬ 
mer. Few of the species that roost in crevices in high cliffs (spotted bat, greater bonnet bat, big free¬ 
tailed bat) have been studied intensively, but they seem to shift roosts less frequently than the above 
species and occur in small groups of one to 30 spotted bats, up to 100 greater bonneted bats, and 
up to 220 big free-tailed bats. Cave-dwelling species are not well studied because of attenuation of 
radio signals within interior chambers underground, but they also do not seem to switch roosts fre¬ 
quently; they can be found in maternity groups ranging from a few dozen or fewer (Mexican long- 
tongued bats), a few hundred at most (Townsend’s big-eared bats), a few thousand (California leaf¬ 
nosed bats) to tens of thousands or more (cave myotis and southeastern myotis). Non-telemetry 
based surveys indicated shifting of roost locations in Townsend’s big-eared bats in areas with mul- 
