Use of Conifer Snags as Roosts by Female Bats in Western Oregon

Abstract

Forest management activities influence habitat suitability for bats, and knowledge of the roosting ecology of bats is fundamental to developing strategies for conserving bats in managed forests. Information on use of roosts by multiple species of bats in a given area may provide insight into interspecific ecological patterns and could improve management prescriptions to provide habitat for bats through time across diverse ownerships and over multiple spatial scales. We investigated use of conifer snags as roosts by females of 3 species of forest‐dwelling bats in Douglas‐fir (Pseudotsuga menzesii) forests in the western Oregon Cascade Range. We radiotagged 29 female big brown bats (Eptesicus fuscus), 55 long‐legged myotis (Myotis volans), and 27 long‐eared myotis (Myotis evotis) and located 42, 105, and 24 snag roosts for the 3 species, respectively. All 3 species most frequently used Douglas‐fir snags and in similar proportions to their availability. Big brown bats and long‐legged myotis rarely roosted in stands <40 years old but age of stands used by female long‐eared myotis did not differ from those randomly available. Odds of a snag being used as a roost by big brown bats increased with diameter at breast height and decreased with distance from the capture site. Diameter of snags used for roosting and the number of small (10–50 cm dbh) snags within the 20‐m radius plot were variables in the best model for roost use by long‐legged myotis. The best model for long‐eared myotis included distance to the capture site. Odds of a snag being used by female long‐eared myotis decreased with increasing distance from the capture site. There was considerable overlap in structural characteristics and the physical context of roost snags among the 3 species, but the types of roosts used among landscapes with differing densities of snags differed among the 3 species. Although big brown bats and long‐legged myotis used only snags and live trees as roosts, long‐eared myotis used a diversity of structures and the frequency of use of these structures differed with density of snags in the landscape. Relative to other roost types, frequency of use of snags by long‐eared myotis was nearly twice as high in landscapes with high densities of snags as in those with low densities. We found that some species of bats alter selection of roosts depending on landscape context and availability of different types of roosts. Our findings demonstrate that forest managers must consider the needs of multiple bat species and the distribution of roosts in the landscape, especially where densities of snags are low and at low elevations in intensively managed landscapes.

Insectivorous Bats and Silviculture: Balancing Timber Production and Bat Conservation

“…This approach has been recommended in published studies (Loeb and Waldrop 2008;; however, other sources report both stand and landscape metrics in North America and Europe to be important in selection of activity areas of bats (Loeb and O'Keefe 2006;Yates and Muzika 2006;FuentesMontemayor et al 2013), with tri-coloured bats, P. subflavus, and eastern red bats, L. borealis, most affected by local stand structure, northern long-eared bats, M. septentrionalis, negatively affected by forest edge, and Indiana bats, M. sodalis, positively affected by dead tree density and non-forested land cover. Other studies corroborate that selection of roosting sites in both bark-and cavity-roosting and foliage-roosting bat species is strongly influenced by landscape-scale metrics in both eastern and western forests of North America (Limpert et al 2007;Arnett and Hayes 2009;Lacki et al 2010). …”

“…In Australia, deadwood removal has been confined to plantations, though recognition of the importance of specifically retaining old trees with hollows in managed forests originated in the 1980s. A preference for roosts in dead and dying trees has been noted for Barbastella and Nyctalus species in Europe (Russo et al 2004;Ruczyński and Bogdanowicz 2008;Hillen et al 2010), and high densities of dead trees appear to be strongly correlated with the presence of roosts of bark and cavity-roosting bats in forested ecosystems across North America (Mattson et al 1996;Sasse and Pekins 1996;Rabe et al 1998;Waldien et al 2000;Cryan et al 2001;Bernardos et al 2004;Broders and Forbes 2004;Miles et al 2006;Arnett and Hayes 2009). …”

Roost Selection by Rafinesque's Big-Eared Bats (Corynorhinus rafinesquii) in a Pristine Habitat at Three Spatial Scales

“…However, roost selection may vary considerably within species based on roost availability. For example, the diversity of roost types used by long-eared myotis (Myotis evotis) increases as the availability of snags on the landscape decreases (Arnett and Hayes, 2009) and niche breadth of roost sites of Nyctalus noctula and N. leiseri increase in managed areas compared to more pristine habitats (Ruczyński et al, 2010). In areas where natural roosts are lacking Rafinesque's big-eared bats are more likely to use a variety of artificial roosts (Trousdale et al, 2008).…”

Roost site selection of western long‐eared myotis in a western juniper woodland

“…Despite the propensity of reproductive females to select rock roost sites when they are available, the flexible roosting behavior of this species allows it to occupy areas where rock roost sites are presumably limited (Vonhof and Barclay , Waldien et al , Arnett and Hayes ). For example, in piñon‐juniper woodlands of New Mexico, female western long‐eared myotis exclusively selected live and dead juniper species as roosts (Chung‐MacCoubrey ).…”

“…For example, in piñon‐juniper woodlands of New Mexico, female western long‐eared myotis exclusively selected live and dead juniper species as roosts (Chung‐MacCoubrey ). Furthermore, in managed conifer forests in the Pacific Northwest, western long‐eared myotis used several types of roosts, and selection was strongly associated with the availability of snags, live trees, stumps, and downed logs (Waldien et al , Arnett and Hayes ). Bats in the present study primarily selected pre‐settlement juniper trees with ≥1 cavity, even though snags, stumps, downed logs, and bark roost sites were available.…”