- Little is known about the fall and winter ecology of hibernating bats in western North America. Filling knowledge gaps for these populations has become more urgent with the westward spread of the white-nose syndrome, a disease that infects bats during hibernation. Due to the thermal requirements of the fungal pathogen that causes WNS, Pseudogymnoascus destructans, WNS infection is dependent on the physiological and habitat conditions that bats experience during hibernation. Knowledge of the life history of western bats in fall and winter, and how their overwintering tactics differ between species, populations, and demographics, will be necessary to understand disease potential and processes in western bat populations. I used radiotelemetry to track Myotis lucifugus and Myotis californicus from late-August to mid-December in 2021 and 2022 at Mount Rainier National Park in Washington State to gather information on fall and winter phenology, movements, and roost use. I captured bats at an M. lucifugus maternity colony and a mixed-species roosting site of male M. lucifugus and mixed-sex M. californicus. I telemetered 28 individuals and identified 38 roost locations in snags and buildings. I observed roost movements up to 13 km and bats using a single roost for up to 23 consecutive days. As the season progressed, all M. lucifugus were no longer detected in either study area, likely moving from transient fall roosts to hibernacula. Compared to the maternity colony, M. lucifugus left the all-male roost an average of 29 days later, suggesting site-level differences in hibernation phenology. All M. californicus remained in the study area, suggesting they over-winter locally. I observed a two-tiered pattern in the duration of roost occupancy for M. californicus in late fall, with short-term roost use (2-6 days) punctuating bouts of long-term roost occupancy (12-20 days). M. californicus were still moving between roosts through the end of telemetry effort in mid-December. To confirm if long-term roost occupancy indicates periods of hibernation by M. californicus, body temperature measurements of roosting bats would be necessary, potentially through temperature sensitive telemetry transmitters or thermal imaging. Tracking bats throughout winter would be necessary to determine if the roosting patterns we observed continue until spring. Observations of nocturnal activities would be necessary to determine if the male M. lucifugus population remained active longer compared to the maternity colony to maximize mating opportunities. Population sizes were small, particularly for M. californicus and from the all-male M. lucifugus roost. Additional studies are needed to determine if my observations are consistent with fall and winter behavior across multiple years, in other bat populations, and from different regions of western North America.
- KEYWORDS: western bats, fall roost, winter bat activity, Myotis lucifugus, little brown bats, snag roost, hibernation, Myotis californicus, Mount Rainier National Park, California myotis, transient roost