January's snow-covered landscape and frigid air likely proabably don't inspire you to think about bats. We associate these fascinating mammals with warm summer nights, when they can be seen fluttering and diving for insects against the night sky. At BiodiversityWorks, however, we think about bats year-round. And we receive calls about bats in every season.
Like all wildlife, bats need food, water, and shelter. During the winter months, when these resources may not be available, bats (depending on species) can either migrate south to find food and shelter, or they can go into torpor. Torpor is a state of reduced physiological activity (lowered heart rate, respiration, and body temperature), which allows animals to conserve energy. When insect food declines and temperatures drop, the bats of Martha's Vineyard put these basic options into play with any of several strategies:
- find an opening to access an attic space with residual heat (big brown bat);
- migrate a short distance to a cave or mine on the mainland with stable temperatures above freezing and high humidity to over winter in torpor (little brown bat and Northern long-eared bat);
- access a damp crawlspace under a home, or an unfinished basement with cinderblock walls, where temperatures remain above freezing to overwinter in torpor (Northern long-eared bat);
- migrate a long-distance south where there is food and water throughout the winter months (silver-haired bat, red bat, and hoary bat).
Our winter calls for bats in or on homes vary as far as how the wayward bat entered the home. Though silver-haired bats are a species known to migrate south for the winter, we have had several calls to homes in December and January for silver-haired bats, and, as seen in our last eNews, a hoary bat too! It is possible these bats flew south to our island from Maine or Canada, and stopped here, taking a chance on overwintering on the island. Compared to Canada, Martha's Vineyard is a milder winter climate. However, when a cold snap occurs we have learned that silver-haired bats will often select a wood pile for shelter and go into torpor within it. Not surprisingly, homeowners are also heading to their wood pile, but to warm their homes. Eventually the two needs collide and a silver-haired bat may be carried into a home on wood where it wakes up later and seeks a way out. The northern long-eared bat, a bat species we research extensively, can overwinter in a cool, damp, crawlspace under a home or an unfinished basement with a bulkhead door. Often the homeowner won't even know that bats are there because bats never chew wood or wiring and because they do not leave much, if any, guano when they are in torpor. During a winter warm spell, however, these bats may become active and be noticed. Or they may accidently make their way into the main section of the house via a vent or chimney. If you have a colony of big brown bats in an attic during winter, one can sometimes find its way into the main house via an air vent or chimney too.
A silver-haired bat found in December inside a house under construction.
A silver-haired bat found on the ceiling of a home in Falmouth. Safely captured using a tupperware bin and a piece of cardboard.
No matter which bat you find in your home in winter, the first rule is never put a bat outside in the cold. For one thing, it is likely too cold outside for a bat out of torpor to survive. But also, people should not handle bats without proper training. You could hurt the bat, or get hurt yourself. Call a professional to help you and to help the bat. If a professional cannot help you, and you must capture the bat, MassWildlife offers guidance on page 5 of their homeowners guide to bats.
A colony of bats in your attic is a different issue from an isolated bat in winter, and it's something you should address at the appropriate time of year. A bat colony can and will occupy an attic year-round, which means urine and guano will build up and cause damage. The homeowners' guide to bats listed above is very helpful. BiodiversityWorks does respond to bats in homes, especially removing an individual bat from a home, but we do not evict colonies of bats. We do, though, maintain a list of trained professionals we can recommend to help you.
The rare and almost extinct northern long-eared bat is losing hibernation spaces beneath homes as people replace older homes with modern, energy-efficient structures. We don't know how many crawlspaces or unfinished basements with bulkhead doors host or have hosted overwintering bats, but we know they hibernate in small groups between sistered floor joists or other small places where they are difficult to see. They only use these spaces in winter. BiodiversityWorks is mitigating this loss of hibernation sites by building hibernacula in safe places for bats. If you find a bat in a basement or crawlspace, or during a demolition, please call us right away. They are likely Northern long-eared bats, and we can help them and you as we now have a safe place where they can continue hibernation. If you have had a bat in your basement during the winter in the last few years, please let us know because that information will help us decide where to build more winter hibernacula for bats.
If you find a bat in your home during winter, call BiodiversityWorks at 508-338-2939 during business hours and we will do our best to help with the situation. After hours, try leaving a message for Liz Olson or Luanne Johnson at (800) 690-0993; our voicemail system will forward your recording as an email.
The outside of our artificial hibernacula at the BiodiversityWorks HQ.
