Big Brown Bats have emerged from hibernation and have been active for several weeks. It is in the spring that a female Big Brown Bat becomes fertilized with sperm she has stored in her uterus over the winter. Reproductive female Big Brown Bats collectively form a maternity roost at this time of year and each bat typically gives birth to a single pup in June, after about a 60-day gestation period.
While both Little and Big Brown Bats were affected by the fungus causing White Nose Syndrome, the Big Brown Bat population has not been decimated like the Little Brown Bat population. In some locations, Big Brown Bats have even thrived, taking over summer roosting spots formerly occupied by Little Brown Bats.
Big Brown Bats, one of the most widespread mammals of North America, are one of the last species of bat to be seen flying in the fall. A relatively hardy species, the Big Brown Bat can tolerate conditions that other bats can’t. However, once cold weather arrives in the late fall and the nighttime temperatures dip down into the 30’s, they go into hibernation.
Both the Big Brown Bat and the endangered Little Brown Bat are considered “house bats,” because they are the most common bats found in houses in both summer and winter. During October, November and December, Big Brown Bats seek out caves, buildings and mines in which to hibernate. Some may migrate short distances to find an appropriate location for hibernating, but many find hibernacula close to their summer residence. Individuals often become active for brief periods during the winter months, sometimes even changing hibernation sites. Big Brown Bats can live up to 18-20 years in the wild but, unfortunately, most Big Brown Bats die during their first winter because they did not store enough fat to survive through their entire hibernation period.
New England is home to both the Little Brown Bat and the Big Brown Bat. While the Big Brown Bat’s wingspan is a bit larger than the Little Brown Bat’s, the physical differences between the two species are quite subtle. If you can get a close look at the face of either one, you stand a good chance of being able to identify it by the shape of its nose and the presence or absence of fur on its face. The nose of the Little Brown Bat is short (and looks as if it has been squished) and it is almost entirely covered with fur, while the Big Brown Bat’s nose is relatively long and there is very little fur between its ear lobes and the tip of its nose.