While Ontario has eight species of bats, only two types, the Little Brown Bat and the Big Brown bat, invade our attics. Both create maternity colonies during the summer months which are colonies of females. These maternal colonies have their young between mid-May to the first of July. Baby bats do not leave your attic for four weeks after being born.
If you find a bat in your house or you can hear them in your attic you most likely have a bat colony in your home as the only bats that invade your attic are bats that colonize. If you see a bat in your home during the winter months, then you almost certainly have a colony. Bats hibernate during the winter months, with the Little Brown Bat travelling to a winter hibernation areas which could be close to its summer home or a few hundred miles away. Little Brown Bats prefer to winter in caves and mines while the Big Brown Bat will often stay to hibernate within your attic. Therefore if you do see a bat in your house during the colder months, it is most likely a Big Brown Bat that has colonized with others in your attic and inadvertently been awakened from hibernation. Little Brown Bats Little brown bats weigh between 5 and 14 g. The length varies between 60 and 102 mm, and the wingspan between 222 and 269 mm. The forearm, including claw, measures 33 to 41 mm, and tail length measures 28 to 65 mm. The hind foot is between 8 and 10 mm in length, ears are 11 to 15.5 mm, and the tragus is 7 to 9 mm. Little brown bats fly at speeds as high as 35 km/hour and average 20 km/hour. Females are larger than males, especially during the winter.
Little brown bats are primarily nocturnal and emerge from their roosts at dusk. Primary activity occurs about two or three hours after dusk and secondary activity may occur before dawn; most individuals return to the roost by four or five o’clock in the morning. These bats usually enter daily torpor. During the winter, hibernation time depends on altitude and location of the roosts. It usually starts between September and November and ends in March to May. The young remain active longer in the fall to build fat deposits to last the winter. Myotis lucifugus does not migrate long distances for hibernation roosts. Individuals travel only up to 100 miles. This species does not show territoriality at roosts, and large colonies of as many as 300,000 bats have been reported in a single roost.
Big Brown Bats Total length of a big brown bat is 110-130 mm, of which the tail is about 38-50 mm. Forearm length is 41-50 mm; hindfoot length is 10-14 mm. Height of the ears from the notch is 16-20 mm. The wingspan is about 330 mm (13 inches). This species is sexually dimorphic in size, females being slightly larger than males.
The skull is comparatively large and contains 32 teeth. The teeth are sharp, heavy, and capable of causing severe bites. The bat’s nose is broad and the lips are fleshy; the eyes are large and bright. The ears are rounded and the tragus is broad with a rounded tip.
Big brown bats are primarily nocturnal and emerge from their roosts at dusk. Primary activity occurs about two or three hours after dusk and secondary activity may occur before dawn; most individuals return to the roost by four or five o’clock in the morning. These bats usually enter daily torpor. During the winter, hibernation time depends on altitude and location of the roosts. It usually starts between September and November and ends in March to May. The young remain active longer in the fall to build fat deposits to last the winter.