We monitored pre-construction bat acoustic activity from 2007 to 2010 at 4 wind energy sites in northeastern British Columbia to determine nightly and seasonal activity patterns, relative detection rates of different species groups, and the implications for potential fatalities at northern wind facilities. Mean activity rates (August to September) ranged from 2.4 to 79.4 passes per detector-night at the 4 study areas. Activity differed between years for 3 study areas with multi-year data. Nightly variation in activity was pronounced, with wind speed and temperature recorded at meteorological towers explaining 47 to 61% of the variation in nightly activity. Detections were predominantly (60 to 96%) of Myotis bats. Only 1 to 18% of passes recorded at study areas were low-frequency bats (Big Brown Bat, Eptesicus fuscus; Silver-haired Bat, Lasionycteris noctivagans; Hoary Bat, Lasiurus cinereus), with L. cinereus accounting for <1% of the low-frequency passes. No Eastern Red Bats (Lasiurus borealis) were detected. Seasonal activity of low-frequency bats showed no evidence of an influx of spring migrants, but single-night activity spikes in late August and early September were suggestive of autumn migration. Activity of Myotis bats was highest in August and early September, a pattern consistent with resident populations. Results suggest that Myotis species may form a larger proportion of fatalities at northern wind energy facilities than at sites in more temperate regions.