Last updated: January 19, 2023
Article
Where Furry, Flying Friends Forage
The Best Coastal Dining Spots for Bats in Southcentral Alaska
NPS/Tim Mullet
Despite the existing research on bats in Alaska (Blejwas 2014, Shively and Barboza 2017, Blejwas et al. 2021), there remains a significant gap in our understanding of their ecological relationships in coastal ecosystems along the northern Gulf of Alaska (Parker et al. 1997, Burger 2020, Mullet et al. 2021). These data are increasingly important as climate change alters subarctic environments and Pseudogymnoascus destructans (Pd), the fungus that causes white-nose syndrome (WNS), continues to spread across the Pacific Northwest (Jung et al. 2014).
The intentions of this study were to (1) determine the species-habitat relationships of foraging bats throughout the coastal regions of Kenai Fjords National Park and (2) model and predict those relationships across the greater Kenai Peninsula to serve as a decision tool to develop more concentrated and oriented studies. We focused our efforts within six dominant landcover classes (alpine, conifer forest, herbaceous, non-vegetated, subalpine shrub, and water) of the coastal zone, including all landscape attributes that occur from the mean high-water line up to 200 m above sea level (Figure 1; Crossland et al. 2005).
NPS/Tim Mullet
Methods
We systematically selected and sampled 25 representative sites throughout the major fjord systems of Kenai Fjords National Park where we deployed SM4BAT full-spectrum Song MetersTM and SMM-U2TM omnidirectional microphones (Wildlife Acoustics, Inc., Maynard, MA) to detect bat echolocation foraging calls, indicated by feeding buzzes. We assigned at least one sample site within a 25-km2 NABat quadrant (Loeb et al. 2015).
We used TreeNet stochastic gradient boosting classification to model the spatial relationships between the point location of presence or absence of bat feeding buzzes and their Euclidean distance to our six landcover classes. We determined our model predictions to be sufficient if the Area under the ROC curve (AUROC) was ≥0.80 and misclassification was <0.15. We then mapped the predicted species-habitat relationships of foraging bats produced by our model within the park to the broader, unsampled, coastal zone of the Kenai Peninsula.
Results
We sampled 1,332 nights and acquired 24,058 recordings of bat vocalizations from June-September between 2018 and 2022 at 23 of 24 spatially explicit locations (one site could not be retrieved). Nineteen sites (79%) had the presence of feeding buzzes. We generally detected little brown myotis (Myotis lucifugus), but a handful of recordings are currently under review for two other species only known to southeast Alaska. Our model performed relatively well with a prediction efficacy of 87.5% (AUROC) and a misclassification rate of 13.5%. The top four most important habitat variables predicting bat foraging behavior were distance to coast, slope, aspect, and distance to conifer forests. Our model revealed that bats foraged within and up to 250 m of conifer forests between 0 and 350 m from the coastline, with southwestern to northern aspects, and moderately sloped terrain <20 degrees.
Kenai Fjords National Park did not possess large or continuous areas of connected high-probability foraging habitat. High-probability foraging habitats generally occurred in patches of old growth conifer forests in areas where glaciers had long receded from the coast. This was also true for high-probability foraging habitat predicted across the coastal Kenai Peninsula. However, larger and more continuous foraging habitat was predicted in the forested coves and deglaciated valleys of the southwestern tip of the Kenai Peninsula adjacent to Alaska Native villages and state lands. Small patches of high-probability habitat were also predicted along the coastlines of some of the larger islands off the southern and east coast of the Kenai Peninsula (Figure 2).
Discussion
On the Kenai Peninsula, little brown myotis are known to use conifer forest habitats (Loeb and Winters 2014), as well as forage over marine nearshore ecosystems off the coast of protected coves and shorelines (Mullet et al. 2021). We found that offshore bat foraging locations in this region averaged 2.25 km from predicted high-probability foraging terrestrial habitats, well within the range of known little brown myotis foraging distances (Henry et al. 2002, Randall 2014). According to our current knowledge, bats that inhabit the coastal zone of the eastern Kenai Peninsula forage along an ecotone of terrestrial and marine habitats ranging from old-growth forests with freshwater streams or ponds to saltwater foraging areas above the open ocean’s nearshore zone.
Our model provides a focused orientation of probable coastal bat foraging habitats with a measure of accuracy (87.5%). These predictions indicate that bats are likely present in many more areas and distributed across a much larger extent than the park alone. Because some of the larger patches of predicted habitat are within areas near Alaska Native villages and state lands, we strongly recommend extending federal, state, and Alaska Native partnerships to survey and monitor these predicted areas with an emphasis on costewardship. These results present a benefit to reducing the information gap on coastal bat ecology in this region as preemptive baseline measure to addressing the risks of climate change and white-nose syndrome to bats in Alaska.
NPS/Tim Mullet
Literature Cited
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