102 
PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES 
Series 4, Volume 65, Supplement I 
mi llimeters (Bogan, 1974; Con¬ 
stantine, 1998b; Verts and Car- 
raway, 1998; Rodriguez and 
Ammerman, 2004). Van Zyll de 
Jong (1985) reported that 50 
individuals averaged 4.9 ± 1.1 
(SE) grams in body mass and 
32.2 ± 0.68 millimeters in fore¬ 
arm length. In a sample of hun¬ 
dreds of individuals from Alber¬ 
ta, Lausen (2007) reported geo¬ 
graphic differences in forearm 
lengths and showed that females 
averaged slightly but significant¬ 
ly larger in forearm length than 
males, with measurements rang¬ 
ing from 29.0 to 38.9 mi ll im eters 
across both sexes (692 individu¬ 
als). In San Bernardino County, Figure 23. Western small-footed myotis, Myotis ciliolabrum (photo by J. 
California, the tip of the tail is Scott Altenbach). 
exserted about 1.5 to 2.5 mi llimeters beyond the tail membrane (Constantine, 1998b). 
In some areas, M. ciliolabrum is sometimes difficult to distinguish from the closely related 
California myotis (M californicus ) even using external and cranial measurements, echolocation 
characteristics, or mitochondrial DNA (Bogan, 1974; Verts and Carraway, 1998; Higginbotham and 
Ammerman, 2002; Rodriguez and Ammerman, 2004; Zinck et al., 2004). Habitat also does not 
always adequately separate all individuals of these two species in such areas, whereas in other 
regions some external characters or cranial measurements appear sufficient to allow accurate iden¬ 
tification (for example, Constantine, 1998b). For these reasons some field researchers report bats 
captured and released as combined M. californicus/M. ciliolabrum rather than attempting to dis¬ 
tinguish among individuals (for example, Black, 1974; Hall, 2000; Chung-MacCoubrey, 2005; 
Geluso, 2008; Geluso and Geluso, 2012; O’Shea et al., 2016b). 
Distribution and Systematics. — The western small-footed myotis is found in western 
North America from Canada to central and southern Mexico (Fig. 24). In the United States, it is 
found from inland Washington, Oregon, and California (occurring on the Pacific coast only in 
southern California) eastward to western regions of the Great Plains states from Texas to North 
Dakota, also extending along the lower Missouri River in eastern South Dakota and Nebraska (Hol¬ 
loway and Barclay, 2001). 
The literature on the distribution and systematics of this species can be confusing and includes 
apparent errors. These bats were considered to fall under the name Myotis subulatus up to the mid- 
1960s, but this name is no longer valid. Glass and Baker (1965) officially petitioned the Interna¬ 
tional Commission on Zoological Nomenclature to formally suppress the name “subulatus” , later 
noting (Glass and Baker, 1968) withdrawal of the proposal and instead formally designating a sub¬ 
species of the small-footed myotis ( Myotis leibii ) as M. leibii ciliolabrum. Van Zyll de Jong (1984) 
further refined understanding of the taxonomic status of these myotis by showing that there are two 
species of small-footed myotis in North America based on cranial morphology: M. ciliolabrum and 
M. leibii. This was later supported by electrophoretic protein analyses at 20 presumptive loci (Herd, 
1987), and by molecular genetic analysis of nuclear amplified fragment length polymorphisms 
