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All 16 species of bats known to occur in western Colorado are found at Mesa Verde National Park (MVNP) in the southwestern United States. Since 1996, wildfires have burned more than 70% of MVNP (>15,000 ha), potentially altering food and roosting resources for bats. During the summers of 2006–2007, we investigated roost use by reproductive female western long-eared myotis (Myotis evotis). We located 33 bat roosts in rock crevices and 1 in a juniper snag. All but 2 of the roosts were in unburned habitat. Bats roosted alone or in small groups (≤3 individuals) and switched roosts frequently (1–7 roosts per bat, median = 1.5 roosts per bat, SE = 0.5 roosts per bat). We compared occupied roosts with randomly selected unoccupied crevices and used an information theoretic approach to determine which variables were most important in determining roost use at microhabitat and landscape scales. At the microhabitat scale, maternity roosts were higher above the ground and deeper than random, unoccupied rock c...

Understanding how environmental factors affect activity, number, and spatial distribution of bats in an area is necessary for interpreting capture rates and assessing abundance. Over a 34-year period, we examined the relationship between amounts of precipitation and activity of bats along a canyon floor in the San Mateo Mountains of New Mexico in the southwestern United States. For 1 night during each of 19 summers, we used identical sampling techniques to monitor this assemblage of insectivorous bats. Years included droughts with minimal surface water and wet years with abundant surface water in the canyon. Marked differences in available drinking water resulted in striking differences in yearly captures of bats, with a 30.8-fold difference between the fewest and most captures (6 versus 185 adults). Capture rates increased with less precipitation before sampling. In the 3-decadal period, precipitation accounted for 66% of the variation in capture rates, providing support that bats concentrate around accessible water to drink when surface water is scarce. Captures also were influenced by relative humidity on nights of sampling. From 1971 to 2005, we detected no change in species composition in this bat assemblage of 8 species, and after accounting for effects of precipitation, we detected no declines in population size for the 2 most common species, the long-eared myotis (Myotis evotis) and long-legged myotis (M. volans). Our study demonstrates the importance of long-term data sets to help elucidate patterns of variability in capture data and highlights the importance of how yearly variation in climate affects the behavior and ecology of bats.

We compared the external morphology of western long-eared myotis (Myotis evotis) living in mountain (cool, wet) and prairie (warm, dry) environments in southern Alberta to test whether flight permits genetic exchange between populations thereby limiting divergence in morphological traits. We measured size of the body (forearm length and mass), ears, and wings for males and females. Ears and wings were significantly larger for bats in the mountains, suggesting that there is limited gene flow between populations despite their geographic proximity, and adaptation to differences in aridity or foraging habitat. However, body size was similar between environments, suggesting that either M. evotis possesses an ecologically flexible body type or that differences in extremity size are the result of environmentally induced phenotypic plasticity. Within environments, females were larger than males for all morphometrics. However, the degree of dimorphism was similar for mountain and prairie populations, indicating that dimorphism is not the result of different thermoregulatory needs in these populations.

Ecomorphological analysis was used to evaluate ecological relationships between 2 species of bats, Myotis auriculus and M. evotis. We imaged jaws and skulls of 242 specimens from 20 localities within the range of both taxa, emphasizing their southwestern regional area of sympatry. Using traditional morphometric and geometric morphometric methods, values for characters taken from dentaries of both species were analyzed in detail. Both methods detected character displacement and allowed us to detect differences in jaw size and shape within both species. The morphological difference in jaw shape is more emphasized within sympatric populations of M. evotis than in M. auriculus. This may indicate that competitive selection acts more on M. evotis. At sympatric localities, M. evotis displayed a shift to a more specialized trophic state with a trophic architecture (more highly placed articular process and robust molars) likely better at capturing beetles, whereas M. auriculus may have a greater advantage for capturing soft-bodied prey such as moths. On the other hand, the articular process is located lower relative to the toothrow of the dentary in M. auriculus. Also the shape of the jaw in this species suggests a weaker bite, more shearing force, and wider gape. All shape differences in jaw morphology are emphasized in sympatry, confirming active competitive interactions between these 2 species.

Bat conservation is hindered by a lack of geographic-specific knowledge of characteristics of roost sites used by reproductive females. We examined roost selection by reproductive female Myotis evotis (long-eared myotis) in the Channeled Scablands of northeastern Washington. We used radiotelemetry to locate 35 roosts of reproductive female Myotis evotis. Habitat variables were measured for each roost itself and at a 0.1-ha microplot and 78-ha macroplot surrounding each roost. We measured habitat variables at random 0.1-ha microplots in the vicinity of each roost and at general random 0.1-ha microplots and 78-ha macroplots. Thirty-four roosts were found in crevices in small basalt rock formations. All radiomarked bats switched roosts at least once and roost switching apparently involved the entire colony. The average number of switches was 3.3 with an average of 2 days between roost switches. The distance traveled between day roosts averaged 148.9 m. Compared to random plots, roosts were in more open, rocky habitats, closer to edge of forest stands, and relatively distant from sources of permanent water.

Jaw and skull morphologies were analyzed in two morphologically distinct species of bats, Myotis evotis (substrate gleaner) and Myotis volans (aerial insectivore). Force vector analyses were performed on five major muscle-bone lever systems to compare the relative adductive forces produced at three functional points (the incisors, canines, and protoconids of the lower second molar) during jaw closure. Relative force produced by contraction of a given adductor was approximated using a modified muscle mass value. Seven angles of dentary position were analyzed for changes in mechanical advantage due to changing muscle fiber orientation. Results of the analyses suggest that M. evotis has a more forceful bite than M. volans , but only as the upswinging dentary approaches closure. Moreover, M. evotis has the potential for a quicker jaw closure than M. volans and the ability to produce series of rapid nipping motions. The masticatory apparatus of M. volans appears well suited for capture of insect prey using a wide gape followed by a forceful closure. These results are interpreted in view of available ecological data concerning the foraging behavior of the two species.

Two extremely similar insectivorous bats, Myotis evotis and M. auriculas , differ in food preferences when sympatric (Black, 1974). Myotis auriculus preys generally upon moths and some beetles, whereas M. evotis specializes on beetles. Does this specialization of M. evotis persist in allopatry, indicating that it has evolved as a food specialist, or in the absence of its close competitor, does it eat both moths and beetles without a strong preference? What sort of effect, if any, does M. evotis exert on the diet of M. auriculus in areas of sympatry? Both species were captured in areas of allopatry during the summer of 1972. Fecal samples were collected and analyzed using Black's (1974) technique. My results indicate that when in allopatry, M. evotis and M. auriculus have similar food habits. Thus, in sympatry, competition for food is avoided by changes in food preferences of M. evotis . Furthermore, each species exhibits sexual differences in foods taken in areas of allopatry, indicating that intraspecific niche subdivision occurs in each of these bats only in the absence of the potential competitor.

A new subspecies of Myotis thysanodes , possibly representing a disjunct population, is described from the Black Hills of South Dakota and Wyoming. The new race is compared with M. t. thysanodes and also with Myotis evotis evotis , which it superficially resembles.