Search

We examined intra- and interspecific patterns of roost-site selection by females of three species of forest-dwelling bats (silver-haired, Lasionycteris noctivagans; big brown, Eptesicus fuscus; and California, Myotis californicus) in the Pend d’Oreille Valley in southern British Columbia. Roost-sites were located by outfitting reproductive and non-reproductive female bats with radio-transmitters and tracking them during the daytime. The tree and site characteristics of roost trees used by each bat species were then compared to those of randomly available trees with cavities, as well as to each other, using logistic regression. All three bat species selected roosts that were taller than cavity trees, and the majority of roost trees were emergent or canopy trees. In addition, tree species and the type of cavity were important predictors of whether trees were used as roosts in both intra- and interspecific analyses. The majority of silver-haired and big brown bat roost trees were in hollows in live trembling aspen trees (Populus tremuloides), but both species used small numbers of roosts on conifer snags. In contrast, the majority of California bat roosts were beneath loose bark on conifer snags, particularly Douglas-fir (Pseudotsuga menziesii), in intermediate stages of decay. In general, site characteristics were only weak predictors of differences between roost and random trees, and roost trees used by the three bat species, but roost trees were found in patches with lower percent canopy closure and greater density of available trees. These results suggest that while all three species of forest-dwelling bats use large trees, within this restricted range of trees there is considerable variation among species in the types of cavities and the tree species used. Maintaining stands containing mature trembling aspen is necessary to provide silver-haired and big brown bats with suitable roosting opportunities, but to meet the needs of California bats, areas rich in conifer snags must be protected. Thus, unique management strategies or silvicultural practices may be required to maintain suitable habitat for all bat species in a given area.

1. 1. Nine of eleven species of desert bats tested demonstrated the ability to initiate and maintain flight at reduced body temperatures. This ability is associated with periodic activity throughout the winter. 2. 2. Of the two species studied most intensively, Pipistrellus hesperus demonstrated a stronger relationship between ambient and body temperatures than did Myotis californicus . It is hypothesized that differences in total body insulation are responsible for the difference in this relationship. 3. 3. Pipistrellus hesperus shows seasonal shifts in actual flight body temperature with a difference of 8–10°C between summer and winter. Spring and fall represent transition periods where the body temperature responds more directly to ambient temperature. Myotis californicus shows the same patterns only to a lesser extent. 4. 4. Low temperature flight appears to be an inherent physiological mechanism with no significant differences observed during laboratory experiments on a sexual or seasonal basis. 5. 5. Some variability is observed which appears to reflect the body condition and caloric and water balance. 6. 6. It is proposed that low temperature flight associated with winter activity is a mechanism adaptive for maintenance of water balance; but only incidentally of value as a feeding strategy.

An examination of the annual changes in brown fat deposits of Pipistrellus hesperus and Myotis californicus reveals: 1. 1. P. hesperus reaches peak brown fat levels in January and February, declining rapidly through March and April, then increases gradually through the remainder of the year. 2. 2. M. californicus , on the other hand, maintains peak levels of brown fat from December through February, decreasing gradually through August, then increasing rapidly in the fall. 3. 3.The major brown fat deposits for both species are interscapular, jugular, squamooccipitocervical and carotid bodies. 4. 4.The interscapular deposit (which accounts for 50–70% of all brown fat) appears to be a good index of brown fat dynamics. 5. 5.Brown fat appears to be important in maintaining body temperature during night at cold ambient temperatures.

An examination of warming rates of chest muscle in relation to rectal temperature and subsequent thermal mapping of selected tissues in active bats has shown the following trends: 1. 1. During arousal, chest muscle warms slightly faster than rectal temperature in Pipistrellus hesperus , Antrozous pallidus, Myotis californicus, M. thysanodes. Eptesicus fuscus , and Tadarida brasiliensis , whereas in Plecotus townsendii chest muscle warms twice as fast as rectal. 2. 2. Bats that warmed sufficiently to initiate flight in the laboratory had interscapular temperatures that were higher than rectal, brain, or adjacent flight muscles. 3. 3. Field data, however, indicate interscapular temperatures to be lower than flight muscle temperature, especially following periods of sustained flight. 4. 4. Both laboratory and field data show that certain bats are capable of coordinated and sustained flight at tissue temperatures well below recognized homeothermic levels.