Graduate Thesis Or Dissertation
 

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

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  • Measuring habitat selection by bats is complicated by their intricate life cycle. Scaling habitat measurements to reflect a hierarchal habitat selection process can help to 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 of eight days per bat, July through August of 1993, 1994, and 1995 in two drainages in the central Oregon Cascades (Quentin Creek and Lookout Creek) to locate day roost structures. 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 was 40 m (SE=2.5). The average dbh for all snags and trees used as day roosts was 100 cm (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 most commonly 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 multiple day roosts within discrete roost areas. The area which encompassed one night roost and all known day roosts covered 3,258 ha in the Quentin Creek drainage and 6,391 ha in Lookout Creek. I compared physical characteristics and habitat within 20 meters of 33 roost snags with 66 randomly selected snags. The odds that a snag is used as a day roost is associated with roost height; given height, the odds of use is associated with the height of the stand within 20 meters of the snag. There is some indication that the presence of an open canopy around the snag, and the percentage of bark on the snag also could be factors that influence the selection of snags as day roosts. The frequency of occurrence of roost structures within young and late seral stands did not differ from what was expected to occur by chance in these two stand conditions. Roosts did not occur in stands with a harvest history vs. stands without a harvest history disproportionate to availability. I compared the distance to class I (largest) through class IV (smallest) streams between 34 day roosts and 102 randomly selected points. Day roosts were located closer to streams than randomly selected locations in both Lookout and Quentin Creek drainages with 1 exception (Lookout class III). In two cases day roosts were significantly closer to streams than randomly selected locations. Day roosts tended to be closer to streams where night roosts were located than did randomly selected points, regardless of stream class.
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