184 
PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES 
Series 4, Volume 65, Supplement I 
Columbia, and may represent 
zones where contact since the 
last glaciation has been relatively 
recent (Herd and Fenton, 1983). 
In most places where the ranges 
overlap, external characters that 
aid in discrimination between lit¬ 
tle brown myotis and Yuma 
myotis include darker ears, more 
gently sloping forehead profile, 
and longer dorsal hairs with 
glossy, burnished tips in little 
brown myotis (Harris, 1974; 
Parkinson, 1979). Figure 37. Yuma myotis, Myotis yumanensis (photo by J. Scott Alten- 
Yuma myotis (Fig. 37) are bach). 
more easily distinguished from other species in the genus (especially in the southwestern U.S.) by 
small size, no keel on the calcar, no dense fringe of hairs on the trailing edge of the tail membrane, 
small ears (less than 16 millimeters) that extend less than two millimeters beyond the snout when 
laid forward, large feet (eight to 11 mm), and small forearm length (32-38 millimeters; Hoffmeis- 
ter, 1986; Schmidly, 1991; Weller et al., 2007; Braun et al., 2015). Autumn weights (when maxi¬ 
mum fat deposition occurs) ranged from 4.8 to 7.8 grams in New Mexico (Ewing et ah, 1970). 
Darkness of coloration is variable between and within locations (Allen, 1919; Dalquest, 1947b). 
Problems that have arisen in field identification of Yuma myotis and little brown myotis in the 
Pacific Northwest have led to suggestions that identification can be enhanced by incorporating 
echolocation characteristics in addition to morphological traits, with Yuma myotis usually showing 
smaller forearm lengths and higher characteristic frequencies of echolocation calls (Weller et ah, 
2007; Rodhouse et ah, 2008; but see also Carraway, 2009 and Rodhouse et ah, 2009). However, in 
cases where 100% certainty is required in this region, a genetic analysis of each individual may be 
needed (Weller et ah, 2007). Genetic characterizations are available for the two species in the Pacif¬ 
ic Northwest (Zinck et ah, 2004; Scott, 2005; Weller et ah, 2007). 
Distribution and Systematics.— In the United States, the Yuma myotis is found from west¬ 
ern Texas, the western Oklahoma panhandle, parts of southeastern Colorado, western Wyoming, 
and Montana west to the Pacific Ocean with major gaps in areas such as the Great Basin and high¬ 
er elevations in the Rocky Mountains (Fig. 38; Harris, 1999; Braun et ah, 2015). The species name 
has been in use since first designated in the late 1800s (Miller, 1897). Six subspecies have been 
named (four subspecies occur in the U.S. with distributions given by Braun et ah, 2015), based 
partly on geographic variation in pelage coloration (Dalquest, 1947b; Harris, 1974, 1999; Braun et 
ah, 2015). Validity of these subspecies designations has not been investigated with modem genet¬ 
ic approaches. Earlier morphological studies suggested the possibility that hybrids between Yuma 
myotis and little brown myotis may occur in those areas of overlap where it is difficult to distin¬ 
guish between them. However, in British Columbia results of protein electrophoresis show no evi¬ 
dence of interbreeding (Herd and Fenton, 1983), nor does mitochondrial DNA analysis of speci¬ 
mens from Washington and Oregon (Zinck et ah, 2004). A summary of other genetic findings and 
hypotheses pertaining to relationships of Yuma myotis with other species of Myotis are available 
in the account by Braun et ah (2015), as is a complete taxonomic synonymy of past scientific 
names. 
The species name is geographically based, after Fort Yuma, California, the site where the type 
