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Climate change is predicted to create increasingly arid deserts with fewer and smaller water sources. Because free water is already limiting for arid-adapted animals, reductions in water likely will impact desert species and how they compete for this limited resource. Our objective was to examine how the size of water sources influenced competition between 2 ecologically similar bats, Parastrellus hesperus and Myotis californicus, in the American Southwest. Bats are a highly successful taxon in deserts, although many rely upon access to free water. We examined bat activity observationally over 35 different-sized water sources throughout the Mojave Desert in southwestern Utah, United States, and experimentally reduced the surface area of 2 water sources. Parastrellus hesperus and M. californicus typically occurred at the same water sources, but both species temporally partitioned their use of shared water sources regardless of the surface area of the water. Experimentally reducing surface area of water sources negatively affected drinking behaviors of both species and resulted in higher overall activity, but temporal partitioning still occurred. While loss of water may influence some competitive interactions, mechanisms such as temporal partitioning can potentially allow continued co-use of limited resources by competing species.

The California myotis, Myotis californicus, and western small-footed myotis, Myotis ciliolabrum, are 2 morphologically similar bats which have had a complex taxonomic history due to intraspecific geographic variation across their sympatric distribution in western North America. Despite several published differences, field identification remains problematic in the southwestern United States. Mitochondrial cytochrome-b and control region fragments were amplified from tissue samples (n ¼ 20) from Texas, Oklahoma, New Mexico, Arizona, Utah, and California to examine species boundaries and phylogenetic relationships. DNA sequences (1,184 bp) were used in parsimony and maximum-likelihood analyses. To corroborate species identification, cranial measurements from all specimens included in the molecular analysis along with additional specimens were analyzed statistically using principal components analysis (PCA). Individuals were designated either as M. californicus or M. ciliolabrum. Molecular analysis placed M. leibii within clades containing both M. californicus and M. ciliolabrum. In addition, sequence divergence and phylogenetic results do not recover distinct lineages for each species (M. californicus and M. ciliolabrum) as recognized by morphology. Our results suggest that these species have recently diverged, or alternatively that they are 1 phenotypically variable species. Based on network estimation of cytochrome-b haplotypes, phylogeographic structure is minimally represented between haplotypes with an east-west separation in the southwestern United States.

The observation of a perceived 4-mm tail extension beyond the border of the interfemoral membrane of the western small-footed myotis, Myotis ciliolabrum , and the absence of the free tail in the California myotis, Myotis californicus , stimulated a quantitative study to determine if the tail character could be verified as a consistent external criterion to differentiate these similar species. Existing study skins were unsuitable for this purpose, because the tail character had been destroyed or distorted by replacement of the tail vertebrae with wire. Twenty-three ciliolabrum and 22 californicus were collected in the Mojave Desert of California and prepared as study skins with tail vertebrae in situ. Examination of these specimens, identified by conventional methods, confirmed that the exserted tail was characteristic of ciliolabrum . Original descriptions, usually based on specimens preserved in alcohol, indicated that the tail character was recognized in ciliolabrum over a century ago.

We followed nine radiotagged female California bats ( Myotis californicus ) to 19 roosts in trees at two study sites in southcentral British Columbia. Bats regularly switched roosts and the number of bats emerging from known roosts fluctuated widely. Logistic-regression analysis showed that reproductively active females preferred trees further away from other trees of the same height or greater, and closer to neighboring trees, relative to available trees in the immediate vicinity of the roost. Diameter at breast height and distance to the nearest tree of the same or greater height explained significant proportions of the variation between roost and available trees found in other areas of the same forest stand. Roost trees had significantly larger diameters and were further away from trees of the same or greater height. Percentage of canopy closure also explained a significant proportion of the variation between roost and available trees, such that roost trees were situated in areas with lower canopy closure than available trees in other areas of the same stand. Roost and available trees were classified correctly >70% of the time based on the above tree characteristics. However, roost trees were only correctly classified 39% of the time in the analysis of site characteristics. Our results, combined with those from other recent studies, lead to the general hypothesis that forest-roosting bats require a number of large dead trees of specific species, in specific stages of decay, and that project above the canopy in relatively open areas. For management and conservation reasons, there should be a strong incentive to evaluate this hypothesis for a variety of species in a variety of locations to test its generality.

Bats were netted at a desert spring in southern Nevada for a total of 70 nights covering each month of the year. Two species, Pipistrellus hesperus and Myotis californicus, were active throughout the year with peaks of seasonal activity during the warmer months. Antrozous pallidus was netted in all seasons of the year. Air temperature was a major factor affecting seasonal and nightly activity with more bats being netted at higher temperatures. However, both M. californicus and P. hesperus were active at air temperatures between −8° and 31 °C. During the warmer months, when air temperatures remained above 15°C for the entire night, both species sustained activity throughout much of the night, but in winter months, they were active only shortly after dusk and activity ceased when air temperatures dropped. Evidence for foraging and insect activity during the winter is presented. The hypothesis of continued year-round activity of bats in warmer areas of the southwest is presented as an alternative to hibernation or migration.

The 0. P. Silliman collection of mammals came to the Museum of Vertebrate Zoology as a gift from Mr. Robert L. Rudd. Most of the specimens were collected and prepared by J. C. von Bloeker and R. L. Rudd. Identifications on the labels are in the handwriting of von Bloeker. Recently, while arranging the collection for cataloging, I examined the specimens upon which the name Myotis ruddi Silliman and von Bloeker (Proc. Biol. Soc. Washington, 51: 167, 1938) was based. All these, except two already in the Museum of Vertebrate Zoology collection, were present in the Silliman collection and with the name Myotis ruddi on the labels. I found that these specimens actually included four species, and that Myotis ruddi is a synonym of Myotis volans longicrus (True). Errors in the technique of labelling and preparing skulls and in identification were evident. All specimens assigned to ruddi were melanistic or nearly so. Six, including the type, are M. volans longicrus, one is Myotis yumanensis saturatus, two are skins of Myotis lucifugus alascensis of which one is accompanied by a skull of Myotis yumanensis and the other by a skull of Myotis californicus. The specimens originally in the Silliman collection were from Monterey County, California. The describers also included one in the collection of the Museum of Vertebrate Zoology from San Benito County, California. Taking the specimens in the order listed in the original description the specimen numbers are now as follows: Lake Espinosa, 50 feet elevation, Salinas Valley, Monterey County: orig. no. 6895, J. C. von Bloeker; 87, 0. P. Silliman; 107900, Mus. Vert. Zool. This specimen is represented by the skin of an immature Myotis lucifugus alascensis. It agrees with other skins of this species from the same locality except that it is slightly darker than the darkest (also an immature) of the other specimens. This series of sixteen specimens exhibits a considerable amount of variation in color. The paler specimens had been labeled Myotis yumanensis sociabilis and the darker ones, except for the one referred to ruddi, correctly assigned to Myotis lucifugus alascensis. The skull accompanying this skin represents an adult Myotis californicus. Fading of the writing on the original skull label may have been the cause for the error since the original label shows that the original number had been retraced, mistakenly, after the skull and label had gone through the cleaning process. It is also evident that some error had been made in recording measurement data on the skin label for some of the measurements had been written over and now are larger than those recorded in the field catalogue of the collector. Chews Ridge, 5000 feet elevation, Santa Lucia Mountains, Monterey County: orig. no. 6457, J. C. von Bloeker; 88, 0. P. Silliman; 107893, Mus. Vert. Zool. This specimen includes a skin of an immature Myotis lucifugus alascensis which had been badly damaged when the bat was shot. The skull associated with the skin is that of an adult Myotis yumanensis. Complete evidence that it is not to be correctly associated with the skin is that the skull is perfect and undamaged 48 Vol.30, No. 1