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PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES 
Series 4, Volume 65, Supplement I 
tiple and complex abandoned min es. Individuals roosting in cavities in saguaro cactus seem to live 
in very small groups (up to five) and also switch roosts nearly daily, but are in need of much more 
study. 
The bats that roost primarily in caves during summer also overwinter in caves, depending on 
region (Rafinesque’s big-eared bats and southeastern myotis do not hibernate in caves in southern 
areas but do so in northern areas of their distributions). Cave myotis (hibemators), Townsend’s big- 
eared bats (hibemators), and California leaf-nosed bats (non-hibemators) make local or regional 
migrations between summer and winter caves in some areas. The Mexican long-tongued bat 
migrates seasonally and does not hibernate. 
Nearly all the species of concern are known to roost in buildings and other human-made struc¬ 
tures to some degree. A lack of reports of buildings used as roosts is only the case for the Samoan 
flying fox, the red fruit bat, Underwood’s bonneted bat, and the California leaf-nosed bat (which 
will use buildings and bridges as night roosts). Buildings are known to be used for maternity groups 
by 14 of the species of concern. 
Winter habits are poorly known for many of the species of concern that roost in rock crevices, 
under talus, and in cracks in boulders and snags during summer. We suspect that in many cases 
these bats winter in inconspicuous deep cracks and crevices in rock or compacted soil. Overwin¬ 
tering of big brown bats in such roosts has recently been demonstrated (Neubaum et al., 2006; 
Lausen and Barclay, 2006; Klug-Baerwald et al., 2017), and our review fails to indicate significant 
use of caves as winter hibemacula for most western species of concern that hibernate. Twente 
(1960:70) offered a speculative explanation that these western species “may hibernate underground 
or in deep crevices in cliffs which remain cold but above freezing” but had no evidence to support 
this notion. The like lih ood that these species hibernate in situations other than caves also was pre¬ 
saged by Griffin (1945:22) for eastern bats: “There remains a speculative possibility that these bats 
may use other places than caves for hibernation, at least in areas where caves are lacking. ...Bats 
would probably be protected from freezing by small deep crevices in rocks such as those used by 
snakes, or even by woodchuck burrows... The habits of bats are too little known to dismiss the pos¬ 
sibility that in caveless areas they may habitually hibernate in unsuspected retreats. Perhaps this 
possibility may add zest to the future field work that is necessary before the life histories of cave 
bats can be satisfactorily understood.” 
Population Ecology.— Although critical for understanding demographic aspects of con¬ 
servation, data related to population ecology of the species of concern vary by topic and by species, 
and in some instances are not well known or not based on large samples. 
Litter Size, Natality, and Female Reproduction: Most species of bats worldwide have litter 
sizes of one or two and this extends to the species of concern. Each of the 20 species typically have 
one young at birth, with the exception of the southeastern myotis (M. austroriparius ), in which 
twinning is very co mm on: a mean litter size of 1.9 occurs in southeastern myotis (based on a very 
large sample), with triplets also reported. Nonetheless, isolated cases of twins and triplets have 
been reported in six other species (Townsend’s big-eared bat, greater bonneted bat, California leaf¬ 
nosed bat, western small-footed myotis, cave myotis, and Yuma myotis), perhaps indicating the 
potential for some minor degree of flexibility in this parameter. Large sample sizes for estimates of 
litter size are not available for some species and are based on six or fewer females as reported in 
the primary literature we reviewed for U.S. populations of the spotted bat, Underwood’s bonneted 
bat, Allen’s big-eared bat, and the Arizona myotis. Litter size estimates for an additional six U.S. 
species are based on samples of 15-28 females (Mexican long-tongued bat, Rafinesque’s big-eared 
bat, western small-footed myotis, long-eared myotis, fringed myotis, and big free-tailed bat). 
Although litter sizes show low variability among species of concern, two other critical aspects 
