O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
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vival and was lower in the area of the spill (Frick et al., 2007; see also “Mortality Factors” and 
“Population Trend” below). These survival estimates were in populations that showed accompa¬ 
nying positive growth in life-history stage-based models (Frick et al., 2007). An overall increase in 
survival with time ranked second to the importance of age group, whereas the effect of spill area 
ranked third in relative importance as a variable affecting survival (Frick et al., 2007). The time 
increase was attributed to the cessation of a major regional drought beginning with the second year 
of study; population growth rates were negative the first year after the spill and became positive 
thereafter, but with growth rates lower in the roosts in the spill-affected area (Frick et al., 2007). 
The maximum longevity record for this species is 14 years (Boutin and Willis, 1996). 
Mortality Factors: A variety of incidental predators on Yuma myotis have been recorded. 
Bobcats were documented regularly preying on these bats at a maternity colony in a cave in Nevada 
(Hall, 1946). The habit of flying low to the ground and over water probably renders them suscep¬ 
tible to various terrestrial and aquatic predators (Dalquest, 1947b). Rabies infections in this species 
are well known (for example, Constantine, 1967; Mondul et al., 2003; Blanton et al., 2007; Stre- 
icker et al., 2010). Eighteen individuals from locations in Colorado were sampled for evidence of 
coronavirus infections but none were detected (Osborne et al., 2011). In spring of 2017, a Yuma 
myotis found unable to fly in King County, Washington was diagnosed with white-nose syndrome, 
indicating this fungal disease occurs in their population (Washington Department of Fish and 
Wildlife, 2017). Given that this species is known to form large colonies during the summer, it is 
possible these bats may aggregate in winter as well, which could facilitate the spread of white nose 
syndrome. Many species of ectoparasites and endoparasites of many different forms have been 
documented in Yuma myotis (reviewed in detail by Braun et al., 2015), but they were not impli¬ 
cated as causing mortality. They have been struck by motor vehicles (Dalquest, 1947b), a likely 
under-recognized source of mortality for bats in general (O’Shea et al., 2016a). 
King et al. (2001) reported on the presence of 18 potentially toxic elements in small numbers 
of Yuma myotis collected at four locations in Arizona in 1998 and 1999. Only copper appeared to 
occur at exceptionally high levels, but the sources and toxic implications of these findings could 
not be determined. Annual apparent survival estimates of juvenile females were lower at two roosts 
near an area of the Sacramento River in California subject to a large spill of the agricultural soil 
fumigant metam sodium (the sodium salt of methyl dithiocarbamate) in comparison with estimates 
for unaffected roosts, perhaps a result of spill impacts on the emergent aquatic insect food base 
(Frick et al., 2007). 
Population Trend: Population growth rates (A,) based on empirically derived life history 
stages ranged from about 1.1 to about 1.2 in a recovering population in northern California (Frick 
et al., 2007; see also “Survival” and “Mortality Factors” above). Sufficient data on U.S. colony 
sizes were unavailable for analysis of count-based population trends (Ellison et al., 2003), although 
a possible local extirpation of small colonies in central Arizona likely due to increased disturbance 
was noted by O’Shea and Vaughan (1999). Brown (2013) noted the absence of Yuma myotis from 
the Senator Mine in California near the lower Colorado River in 1991 and 2011, whereas Howell 
(1920a) reported a colony of about 600 females at this site. 
Weller (2008) evaluated sampling design considerations for use of occupancy estimation mod¬ 
els to assess population status and habitat associations of Yuma myotis in the Pacific Northwest. 
Occupancy was determined using both captures in mist nets and echolocation recordings during 
four surveys at 51 carefully selected sites in Washington, Oregon, and northern California, and esti¬ 
mated based on a series of habitat models (including successional stage and reserve categories) that 
were ranked using Akaike’s Information Criteria. They were detected at 27 sites (observed occu¬ 
pancy of 0.529). Model-averaged detection probability estimates were 0.447 ± 0.07 (SE), and over- 
