There are eight different species of bats that live in Ontario - the most common of these is the "little brown bat."  Bats normally roost in trees or caves but due to urbanization bats can often be found roosting in man-made structures, especially attics. This is the primary reason that bats come into conflict with people. The bats living in Ontario migrate or hibernate during the winter months. Due to the small size of bats they are able to gain entry to an attic or other spaces through a hole as small as a half-inch. This can make it difficult to find all possible entry/exit sites used by the bat(s), but it is important to investigate thoroughly and find all the access points if possible.  Excluding bats from your home is difficult and definitely requires professional consultation.