Selection of day roosts by female long-legged myotis (Myotis volans) in forests of the Central Oregon Cascades

Measuring habitat selection by bats is complicated by their intricate life cycle.Scaling habitat measurements to reflect a hierarchal habitat selection process can helpto define habitat associations of bats. I assessed day roost habitat of female long-legged myotis at four scales: the roost structure, micro-habitat surrounding the roost,the stand level, and landscape level.
I radio-tracked 16 female long-legged myotis (Myotis volans) for an average ofeight days per bat, July through August of 1993, 1994, and 1995 in two drainages inthe central Oregon Cascades (Quentin Creek and Lookout Creek) to locate day rooststructures. Forty-one day roost structures were identified, of which 1 was a rock face,4 were green trees, and 36 were snags. The average height of all roost structures was40 m (SE=2.5). The average dbh for all snags and trees used as day roosts was 100cm (SE=6.1). Large snags including partially live, hollow western redcedar trees(Thuja plicata) averaging 97 cm dbh (SE=6.6) and 38 m (SE=2.8) high were the mostcommonly used roost structures.
Individuals radio-marked at the same night roost did not use one common day roost.Individual bats were found roosting in one roost for several days, or using multipleday roosts within discrete roost areas. The area which encompassed one night roostand all known day roosts covered 3,258 ha in the Quentin Creek drainage and 6,391ha in Lookout Creek.
I compared physical characteristics and habitat within 20 meters of 33 roost snagswith 66 randomly selected snags. The odds that a snag is used as a day roost isassociated with roost height; given height, the odds of use is associated with the heightof the stand within 20 meters of the snag. There is some indication that the presenceof an open canopy around the snag, and the percentage of bark on the snag also couldbe factors that influence the selection of snags as day roosts.
The frequency of occurrence of roost structures within young and late seral standsdid not differ from what was expected to occur by chance in these two standconditions. Roosts did not occur in stands with a harvest history vs. stands without aharvest history disproportionate to availability.
I compared the distance to class I (largest) through class IV (smallest) streamsbetween 34 day roosts and 102 randomly selected points. Day roosts were locatedcloser to streams than randomly selected locations in both Lookout and Quentin Creekdrainages with 1 exception (Lookout class III). In two cases day roosts weresignificantly closer to streams than randomly selected locations. Day roosts tended tobe closer to streams where night roosts were located than did randomly selectedpoints, regardless of stream class.
Maintaining large diameter, tall, solitary snags and patches of snags across all seralstages would be a reasonable step toward providing day roost habitat for long-leggedmyotis in managed landscapes. Managing for specific roost structures and the areaaround the roost structure may be desirable under some circumstances.
Further research and monitoring should include testing methods for aerialmeasurements of roost structure and canopy characteristics. More detailed analysis ofroost structure characteristics such as bark, and stand characteristics such as numbersand types of snags present would increase the level of precision for characterizing dayroost habitat. Further study of fidelity to roost areas and the influence of microclimaticconditions in and near different types of roosts would provide insight to the functionof roosts and roost areas. Studies on the association of day roosts, night roosts, andforaging areas would provide a more complete picture of habitat utilization.