As white-nose syndrome and other threats have decimated bat populations in North America, the need to understand bat roosting affinities and population dynamics becomes more critical. Our knowledge of bats’ roosting habitat has been biased by what locations are easily accessible to humans, such as caves, mines, and anthropogenic structures. A citizen science project, Climbers for Bat Conservation, is using recreational climbers to identify bat roosting habitat that is typically outside of human reach. Started in 2014, CBC has developed collaborations with some of the largest climbing advocacy and conservation groups in the world, including Access Fund, American Alpine Club, The Climbing Initiative, and Petzl. CBC has nearly 300 records of bats along cliffs and rocks from U.S., Bulgaria, Italy, Norway, and Kenya. Passively-collected observations continue to feed CBC’s database, but active climbing surveys are now being implemented to look for bats and identify roosts. Utilizing recreational citizen-science data CBC is opening new avenues to investigate bat habitat and locate bat populations.

Mitigation for the loss of bat habitat is often a requirement under the California Environmental Quality Act. However, artificial habitat does not always maintain the same habitat value as previously available habitat, particularly for habitat specialist species like the Townsend’s big-eared bat (Corynorhinus townsendii) or habitat that supports maternity roosting bat colonies. From 2015 to 2023 the Midpeninsula Regional Open Space District, with technical expertise from H.T. Harvey and Associates, worked to develop and implement a bat exclusion and habitat replacement plan to address a loss of habitat due to the demolition of buildings found within Bear Creek Redwoods Open Space Preserve, in Santa Clara County, California. This work included the construction of two new freestanding structures, as well as the modification of an existing structure specifically to attract and support Townsend’s big eared bats, a California State Species of Special Concern, as well as a variety of more common crevice roosting species. The new and modified structures were monitored for bat activity by conducting annual emergence surveys during the maternity roosting season, as well as opportunistic daytime surveys during non-sensitive seasons. In-situ temperature probes were also utilized to determine annual thermal characteristics of the interior of the structures to determine habitat suitability and inform management decisions. Surveys have documented an increase in bat use through time, as well as confirmed maternity roosts of common bat species, at each of the replacement habitat structures. Townsend’s big-eared bat have been documented utilizing the interior of the modified existing structure as a presumed bachelor roost. Exterior bat boxes on all structures support the majority of individual bats on-site and are utilized by four common species of bats. The habitat use, number of individual bats, as well as species composition on-site is similar to what was documented by surveys prior to the demolition project. Habitat value at these structures is dynamic as exterior boxes degrade and require replacement, vandalization of structures requires ongoing maintenance and modification, and new crevice roosting habitat becomes available as the structures shift and degrade through time. The findings from this project can inform bat mitigation and monitoring work, particularly for Townsend’s big-eared bat, and offer strategies for improved outcomes.

Insectivorous bats are considered indicators of ecosystem health due to their ability to occupy a wide variety of habitats as well as differing thermal niches. Therefore, investigating how insectivorous bats respond to habitat variability in an area that has not only long been susceptible to wildfires, but has been managed for fires through fire suppression, gives insight to population persistence not only for bats but for a variety of other small mammals. In 2020, Sequoia and Kings National Parks experienced a wildfire that spanned 3636 ha within park boundaries. We tracked eight California myotis bats (Myotis californicus) to 22 roost sites from June – August 2021 in an area with unburned to severely burnt habitat. The majority of M. californicus roosts (21 out of 22) were positioned within or <5 m from the burn mosaic, although unburned habitat was easily accessible. However, M. californicus showed preference for roosts located in low-severity burn areas, rather than severely burnt habitat. This study demonstrates that while wildfire may be beneficial for certain bat species, severe wildfire could be detrimental to some bats in summer by reducing canopy cover and altering or destroying preferred roost trees.

Culverts are sometimes mentioned in the context of anthropogenic structures providing bat roosting habitat; however, there is a paucity of available information about these roosts. Data collected throughout Southern California over a 15-year period show that at least eleven bat species roost in various culvert types; these include concrete box, arch, and pipe culverts as well as corrugated metal pipe culverts. Occupied culverts are found in a variety of habitats, including heavily urbanized landscapes, and bats have been observed day roosting (including maternity roosting), night roosting, and even mating within culvert structures. Features used by bats in culverts vary widely and can include overlap joints, expansion joints, manhole access shafts, drainage pipes, open surfaces, and bird nests. Misconceptions about what constitutes suitable roosting habitat in culverts can result in these structures being overlooked during environmental review, and consequently impacts to bats roosting in culverts are often not adequately mitigated. Bats roosting in these structures are also vulnerable to disturbance from human entry, vandalism, and increases in artificial light at night (ALAN) in adjacent areas. Because roosting habitat is a limited and declining resource for bats, overlooking culverts or less-commonly encountered features in culverts as roosts can have profound conservation implications.