Big Brown Bat (Eptesicus fuscus)

(Thank-you to Dr. Merlin Tuttle, Bat Conservation International for use of this picture)

The big brown bat is one of the most common bats in Canada. These bats are one of the larger bats, weighing on average 15 grams (53 oz's), with a recorded high of 21.9 grams (77 oz's). Their wing span is about 33 cm (13 inches). Fur colour ranges from pale to dark brown, with an oily texture. Flight membranes and ears are black. They seem to prefer schools, houses, barns and churches as roosting sites, making it one of the more commonly encountered bat. Big browns have a solid, heavy jaw which allows them to eat hard shelled beetles. They seem to prefer to travel less than 80 km to locate their hibernaculum, but some have been found as far as 300 km from their summer roosts. Big brown bats are the only Alberta bats to hibernate in human buildings - not always successfully. Interestingly, there are more big brown bats in Edmonton in the winter than there are in the summer! They are hardy individuals, able to sustain temperatures as low as -10˚C, but preferring temperatures in the 0˚C to -4˚C. They will typically lose 25% of their body weight while hibernating! They live up to 20 years. This species of bat, is widespread in North America. There are many things not understood about bats, but with this particular species, it is unknown why the eastern version of big brown bats often deliver twin pups, but the western version delivers only single pups!