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Bats of the temperate region of North America avoid winter by some combination of migration and hibernation at a location that provides the right conditions for minimizing energy expenditure over winter. Such optimal conditions are commonly found underground, and most of the best known hibernacula occur in caves or mines. Where winters are milder, some bat species hibernate in hollows in trees. Haida Gwaii, British Columbia, has the dual distinction of being relatively far north in terms of bat distribution, but with a relatively moderate oceanic climate. We hypothesized that because of the moderate winter temperatures, hibernating in trees could be an option for bats on Haida Gwaii. We used data loggers to monitor temperatures inside potential roost trees during 9 winters between 2002–2003 and 2012–2013. We found that mean winter temperature inside the trees ranged from 2.3–6.5°C, and in most years …