O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
51 
recording returns of yearling and adult females to a maternity site each year for three years (thus 
emigration must be assumed to be negligible). Adult return rates were 70-80%, whereas yearlings 
returned at a rate of roughly 40 to 50%. Stable colony sizes were considered likely if recruitment 
of young was 50% the first year and survival of adults was 80% annually (Pearson et al., 1952). 
Pre-weaning mortality in this species is thought to be about four to five percent (Pearson et al., 
1952; Humphrey and Kunz, 1976). 
Survival analyses using modem analytical methods were carried out retrospectively on band¬ 
ed Townsend’s big-eared bats using three cave systems as hibemacula in Washington (Ellison, 
2010). Banding took place during 1964-1975 with 1,123 individuals banded and recaptures con¬ 
tinuing until 1980. Annual apparent survival estimates varied from 54% to 76% using model-aver¬ 
aging techniques, survival tended to be lower in males than in females, and estimates of capture 
probability ranged widely. The cave system with the largest sample size showed an upward trend 
in survival with time through 1980, but it had a negative trend in capture probabilities (Ellison, 
2010). Basic survival estimates were mostly lower than those calculated for other species of tem¬ 
perate zone bats with similar demographic traits that had stable or growing populations (O’Shea et 
al., 2011c). Banding at this site was known to cause injuries to this species, and banders thought 
that the associated disturbances may have had negative impacts (perhaps including permanent emi¬ 
gration) that were reflected in the estimates (Ellison, 2010). Newer efforts to conduct survival 
analysis on this species are underway in western Colorado, where over 600 individuals have been 
marked with PIT tags at a summer roost equipped with devices that automate the recording of bat 
presence and activity (Siemers and Neubaum, 2015). 
Townsend’s big-eared bats banded in California provided a published maximum longevity 
record for this species of 16.4 years (Paradiso and Greenhall 1967). 
Mortality Factors: Known mortality factors include incidental records of predation by gopher 
snakes (Pituophis melanoleucus ) in caves (Galen and Bonn, 1979), by black rats (Rattus rattus) in 
buildings (Fellers, 2000), and by domestic cats at entrances to gated caves occupied by Townsend’s 
and Virginia big-eared bats (Bagley and Jacobs, 1984; Jewel Cave National Monument, written 
commun.). Townsend’s big-eared bats are subject to deaths from rabies (for example, Constantine, 
1979, 1988; Mondul et al., 2003; Blanton et al., 2007). Ectoparasites and endoparasites have been 
described but not linked with mortality (for example, Jameson, 1959; Rausch, 1975, Reisen et al., 
1976; Ritzi et al., 2001; Sastre et al., 2016; for summary of earlier work see: Sparks and Choate, 
2000; Whitaker and Wilson, 1974). In their intensive study of this bat in California where over 
1,500 individuals were banded and subsequently searched for over several years, Pearson et al. 
(1952) suggested that disease and predation were unlikely to be factors limiting population size, 
but that the number of suitable winter roosting sites and summer roosts with adequate feeding areas 
were critical. 
Chemical residue surveys for contaminants have been carried out in guano and carcasses of 
the endangered subspecies of Townsend’s big-eared bats (Martin, 1992; Ryan et al., 1992), but 
deaths due to chemical contaminants are unknown. A colony of these bats was likely eliminated by 
mortality due to exposure to cyanide in drinking water from a gold-mining operation in California 
(Brown and Berry, 1991; Clark and Hothem, 1991). Potential absorption of radon was estimated 
for this species using caves and abandoned uranium mines at 7 micrograms per year during winter 
and 139 micrograms per year during summer, but the health effects of such exposure remain 
unknown (Schmidt, 2014). 
Blood samples from three individuals sampled from a cave in western Oklahoma during Feb¬ 
ruary of 2011 were negative for antibodies to Pseudogymnoascus destructans, the fungal agent of 
white-nose syndrome (Brennan et al., 2015). Although white-nose syndrome has been document- 
