Foraging habitat drives the distribution of an endangered bat in an urbanizing boreal landscape

Abstract

The boreal forest is the largest intact forest in the world, and a refuge for species experiencing range retractions as a consequence of climate and landscape change. Yet, large tracts of the boreal forest are threatened by the cumulative impacts of climate change, natural resource extraction, agriculture, and urbanization, perhaps warranting a shift in focus from biodiversity conservation in intact wilderness to that in anthropologically modified landscapes. We investigated landscape features that influence the distribution of the endangered little brown bat (Myotis lucifugus) in an urbanizing boreal landscape at two spatial scales. We hypothesized that little brown bat activity would be influenced by proximity to available building roosts, because roosts are a potential limiting factor for boreal bats. Secondarily, we predicted that bats would use potential foraging habitat, such as waterbodies, and would avoid young, cluttered forests at the landscape scale. We conducted acoustic surveys of bat activity at 210 sites distributed across the study area in Yukon, Canada, within 1-km grid cells. We tested a priori hypotheses with a set of candidate regression models, accounting for spatial autocorrelation. Our hypothesis about the relative importance of anthropogenic roosts was not supported. Little brown bats were equally active in urban areas (high building density) and rural areas (low building density), perhaps because roosts were adequately available throughout the region. Instead, habitat use was driven by the distribution of potential foraging habitat, particularly waterbodies, which are important sources of aerial insect prey. Little brown bats also avoided young (≤100-yr-old) forest at the landscape scale (including areas regenerating after fire), which may have been poor foraging or roosting habitat, and used areas with a smaller agricultural and industrial footprint. Our results suggest that waterbodies and mature forest are important little brown bat habitats that should be protected from urban encroachment. Proactive conservation of important habitat for species at risk is still possible throughout much of the boreal forest, where human densities are comparatively low and the urban footprint is currently small.

Little brown bat activity patterns and conservation implications in agricultural landscapes in boreal Yukon, Canada

“…The patterns of habitat use that we recorded generally support the prevailing paradigm that little brown bats travel and feed most intensively at ponds and along riparian edges and do so less frequently along nonriparian edge habitats and in forest interiors (Nelson & Gillam, 2017; Thomas et al, 2021). We found this pattern repeatedly, with particularly high use by bats of the riparian edges of ponds in numerous settings, more moderate use of nonriparian field edges and forest interiors, and least use of open fields at a minimum of 140, 150, and 220 m (sites 2d, 7d, and 8a) from the field edge.…”

“…Thomas and Jung (2019) found that in rural Yukon, Canada, villages provided islands of bat roosting habitat within a forested landscape where roosting opportunities were presumed to be fewer. Working in essentially the same study areas as ours, Thomas et al (2021) predicted that some level of forest clearing, such as agriculture, would improve bat habitat by increasing habitat heterogeneity in a relatively homogeneous forested landscape. Instead, they found that acoustically recorded bat activity declined as extent of forest clearing increased from 1% to 50% of the area within 1 km of the recorder.…”

“…For fields, years since conversion from forest and crop type are described in Table 2. We focused particularly on different types of riparian edges around still water (“ponds”), given the documented relatively heavy use of these habitats by little brown bats (Grindal & Brigham, 1999; Thomas et al, 2021). Ponds ranged in size from approximately 0.1 to 1.4 ha, except for one oxbow pond at 10.1 ha.…”

“…Various studies have demonstrated a general pattern in the little brown bat's relative use of different habitat features in forested landscapes: the bats typically travel and feed most intensively at ponds and along riparian edges and do so less frequently along nonriparian edge habitats, and in forest interiors (Nelson & Gillam, 2017; Thomas et al, 2021). Slough and Jung (2008) used acoustic surveys to monitor bat activity in Yukon and found the greatest activity at edges of riparian and lacustrine habitats, including shorelines and overwater.…”

“…Although the greatest diversity of bats is in the southwest United States, the greatest proportion of bat species that are at risk occurs in eastern and northern North America, including the vast boreal forest (Hammerson et al, 2017). The boreal region, with its lower human population density and fewer associated developments, has been described as a refuge for wildlife species, including little brown bats, that were experiencing population declines and habitat losses, prior to the spread of white‐nose syndrome, in the more southern parts of their ranges (Berteaux et al, 2018; Thomas et al, 2021). Not all developments and habitat losses are locally driven, however.…”