At Bat Free LLC we have heard many customers say that bats fly south for the winter. Is that true? It is not true of all bat species. In the upper midwest, Little brown bats and big brown bats tend to winter in human structures. Here they enter a state of mental and physical inactivity called torpor. In this state, they experience a metabolic shutdown that slows their heartbeat from 400 beats per minute to 25 beats per minute.
Bats may hibernate for as long as 83 days, slowly metabolizing the body fat they stored up in the fall. In the spring as the sun gets higher in the sky and daytime temperatures begin to rise, bats wake from torpor and become active. Our clients begin to hear them chirping, scratching, and hissing. Should the nighttime temp cool sufficiently, the bats go back into a deep sleep(torpor) until the temperatures rise again. The bats will begin their nightly process of leaving the structure to forage for food when the overnight temperatures stay above 50 degrees for 5 nights in a row.