A few big brown bats hibernate in caves and mines in winter, usually near the entrance in small numbers.
It is not clear why Indiana myotis continue to do so well at Wyandotte Cave when the temperature in the areas where the bats hibernate is about 10[degrees] C, whereas their preferred hibernating temperature is about 2-6[degrees] (Hall 1962).
Through the winter of 2001-2002 there were guided tours through the cave, and these tours went directly under one of the main areas (Washington Avenue) where the bats hibernate. Thus, data from this cave suggest that the non-visitation policy is not necessary to conserve energy for successful hibernation, as the bats have continued to increase even in the face of regularly occurring visits, often several per day.
More bats apparently hibernate in the cave because of gating changes that improved airflow and are more bat-friendly.
We used Ibutton Thermocron data loggers (Dallas Semiconductor Corp., Dallas, Texas) to monitor temperatures in crevices or hollows and under the bark of potential bat roost trees to determine if it was feasible for bats to hibernate in trees on Haida Gwaii.
In 2005-2006, 2010-2011, 2011-2012, and 2012-2013 we placed data loggers both inside and under the outer bark of 1 of the study trees (SI #1) to assess whether a bat could hibernate under the bark.
To further explore the feasibility of bats hibernating in hollows or crevices in trees on Haida Gwaii, we used the formulas of Humphries and others (2006) to determine how much fat would be required for a Little Brown Myotis to hibernate in trees, with one exception.
Using the temperatures recorded in our experimental trees we calculated the amount of fat required for a 6 g bat, the approximate mass of Little Brown Myotis in summer on Haida Gwaii (Buries and others 2009), to hibernate in each of our study trees from 1 November to 30 April the following spring.
Our assumption was that by September bats would be congregating near where they were going to hibernate and we might be able to track them to their hibemacula.
Both the results of our monitoring of potential hibernation sites and the temperature data obtained from the Sandspit airport support our hypothesis that it would be feasible for bats to hibernate in trees on Haida Gwaii.
The results of our calculations of energy requirements also support our hypothesis that a bat could hibernate inside our study trees.
comm.), possibly suggesting that they migrate somewhere on or off the islands to hibernate.