Graduate Thesis Or Dissertation
 

Resource Selection and Space Use of Western Long-eared Myotis (Myotis evotis) in a Western Juniper (Juniperus occidentalis) Woodland of Central Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/bk128f573

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  • Identifying habitat and spatial requirements of wildlife species across multiple spatial scales is a challenging, yet crucial component of wildlife management. Habitat use of bats is particularly difficult to study, and managing habitat to conserve bats is especially challenging because bats are highly vagile organisms that exploit several different types of habitat across many spatio-temporal scales. The status and distribution of bat populations is determined by the spatio-temporal pattern of quality roost sites and foraging areas across the landscape. However, knowledge of these limiting resources for bats and their distribution on the landscape is poorly known in western juniper (Juniperus occidentalis ssp. occidentalis) woodlands, even though at least 16 species of bat occur in these habitats across the western United States. Identifying habitat use by bats in western juniper woodlands is especially important due to recent landscape-scale efforts to remove juniper trees to improve habitat for greater sage-grouse (Centrocercus urophasianus), a species of major conservation concern in shrub-steppe habitats. Thus, the urgent challenge for land management agencies in western North America is to identify bat day roost and foraging sites in order to develop management guidelines to conserve bats and their critical habitats. The specific objective of this study was to identify habitat characteristics that are important to western long-eared myotis (Myotis evotis) during the reproductive season in western juniper woodland of central Oregon. I used radio telemetry to find day roost sites and investigate selection criteria for these sites by lactating female and male bats. I studied day roost site selection at three spatial scales: roost, plot, and home range. I found that females prefer to roost in rocks rather than in trees, whereas males did not display a preference towards either type of roost substrate. Bats that roosted in trees used primarily pre-settlement junipers (> 150 years old) with at least one cavity, and bats that roosted in rocks used primarily formations consisting on multiple boulders. More available roost sites within 17.8 m of a tree roost site (or within 5 m of a rock roost site) was associated with an increased likelihood that a particular tree or rock roost site was selected. Males selected rock roosts that had greater area of pre-settlement woodlands than shrub-steppe within a 1 km radius. These results suggest that roost site selection differs between lactating females and males and occurs at multiple spatial scales. Land management practices that retain pre-settlement trees during juniper removal treatments and protect areas with high densities of roost sites near water sources are likely to conserve or restore bat populations. I also estimated home range size and the maximum foraging range of bats. Estimates of mean home range size were the largest ever reported for western long-eared myotis and among the largest for any Myotis species so far studied in North America. The mean 95% home range size for lactating females was 205.85 ha (SE = 47.94) and for males was 424.2 ha (SE = 187.2). The mean maximum foraging range for lactating females was 933 m (SE = 284.9) and males was 1522 m (SE = 532.8). Estimates of mean home range size and maximum foraging range did not differ between lactating females and males; however, low statistical power likely precluded detecting a difference. Lastly, I examined habitat selection at two spatial scales, (1) home range selection on the landscape scale and (2) foraging habitat selection within the home range. The probability of a location being selected by either lactating female or male bats decreased with increasing distance from day roost sites and water sources. Lactating females selected pre-settlement woodlands more than shrub-steppe habitat during foraging, but avoided areas with > 20% tree canopy cover more than areas with no canopy cover at the landscape scale. Males selected areas with 0.1% to 10% tree canopy cover more than areas with no canopy cover at the home range scale. To maintain foraging habitat for M. evotis in the study area, pre-settlement woodlands that are located near roost sites and water sources should be managed for variable tree densities.
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