O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
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vation Need Tier IB (as M. occultus). California Department of Fish and Wildlife (2017): Special 
Animals List, Species of Special Concern (as M. occultus). New Mexico Department of Game and 
Fish (2015): Species of Greatest Conservation Need, Sensitive (as M. occultus ). 
Description. — The Ari¬ 
zona myotis is a medium-sized 
myotis, with a body mass of 4-9 
g (Ewing et al., 1970; Ammer- 
man et al., 2012a). Mean forearm 
lengths in various populations 
range 35.7 to 40.8 millimeters, 
with an overall mean of 37.9 mil¬ 
limeters (calculated from Findley 
and Jones, 1967). Overall 
appearance (Fig. 29) is similar to 
the little brown myotis 
(M. lucifugus), but often with a 
reddish or auburn tinge to the 
dorsal fur and tan or light brown 
ventral pelage. This species can 
be distinguished in hand from most sympatric species of myotis because the wing membranes and 
ears are dark to black in color rather than light-colored as in the slightly smaller and lighter-col¬ 
ored Yuma myotis, and because the calcar is keeled and the underside of the wing membrane is 
more densely furred in the long-legged myotis (M. volans). There is no keel on the calcar of the 
Arizona myotis, unlike the similarly sized long-legged myotis, and the smaller California myotis 
and western small-footed myotis. Ear length (about 13 millimeters, range 11-16 millimeters; 
Hoffmeister, 1986) is typically smaller than long-eared myotis, fringed myotis, and southwestern 
myotis (M auriculus). The cave myotis (M. velifer) is larger and has a sparsely furred region on 
the back between the shoulders. 
Distribution and Systematics. — In the United States, the Arizona myotis is found from 
southwestern and south central Colorado southward, throughout New Mexico and Arizona to 
southeastern California (Fig. 30) and perhaps extreme western Texas (where only a single record 
is known; Ammerman et al., 2012a). There are no recognized subspecies. The generic name Myotis 
stems from Greek roots meaning “mouse” and “ear”; the specific epithet occultus is Latin for “hid¬ 
den” or “mysterious”. Simmons (2005) uses Arizona myotis as the common name for this species. 
Other English common names include occult myotis, occult bat, Arizona occult bat, southwestern 
little brown myotis, occult little brown bat, and Hollister’s bat. 
The taxonomic status of the Arizona myotis has been in flux because various assessments have 
been made over the years using increasingly sophisticated methods. The most recent analysis treats 
the taxon as a full species (Piaggio et al., 2002). This status is recognized by standard mammalian 
taxonomic authorities such as Simmons (2005) and Bradley et al. (2014). However, some authors 
remain hesitant about the status of this taxon as a full species (for example, Armstrong et al., 2011; 
Dewey, 2006). Given past uncertainty and likely confusing expert opinions about the taxonomic 
status of this species, below we provide a history of the factors influencing past changes to the 
species nomenclature. The Arizona myotis is an endemic southwestern taxon with regional varia¬ 
tion in cranial morphology and dentition, and a complex and only partially understood evolution¬ 
ary history. Regardless of past debate regarding species status, Piaggio et al. (2002:393) point out 
that “we think it would be a mistake to assume that if population declines of M. occultus occur, 
Figure 29. Arizona myotis, Myotis occultus (photo by J. Scott Altenbach). 
