Bats in the Fall

Bats function on a strict yearly cycle. They go into hibernation in the winter, they emerge in the spring to ovulate and give birth, they raise their young and wean them in the summer and spend the rest of summer and the fall fattening up for the hibernation in the winter. They stick to this yearly schedule and it is necessary to understand this process in order to be able to successfully handle a bat infestation.

What are bats doing in the fall?

By mid to late September, bats are preparing to start their migration to their winter hibernation sites. They have been feeding all summer long and have built up the fat stores that they need to survive the harsh winters of Michigan. They will save as much of these fat stores as possible and keep within a few miles of their home range to find a suitable hibernation site.  Bats do not have to travel for thousands of miles to reach these sites. It is more likely for them to stay close to where they spend their summer. Some bats, like the big brown bats native to Michigan, may remain at the same roosting sites where they had their pups.

What triggers them to hibernate?

Cool nights and a decrease in insect activity are the triggers for the bats to begin their search for good hibernation sites. The big brown bats prefer to hibernate above ground and have found that attics and inside the walls of homes are great areas for their hibernation needs. These areas provide stable temperatures that are suited to what it is they require for a healthy hibernation. These areas make it possible for them to slow down their metabolism just enough to make their fat stores last but not too cold to where they are going to freeze.

How should people handle a fall infestation?

If people notice that they are having a bat problem and it is the fall, they need to act quickly. By late October, middle of November at the very latest (if there was a warm spell), bats are making their way into their hibernation sites.  If it is not dealt with by the time winter hits, they are going to have to wait until spring in order to remove the bats from their home. Bats are not going to fly out of their hibernation roosts in the winter and their flight patterns are necessary for successful exclusion.

Exclusion is a process that any certified local professional is able to assist with. It involves a homeowner observing where the bats are coming and going from so that they know where the weak parts of the structure are. Then homeowners, or their local professionals, will come in to install one-way doors so that the bats are able to get out but not get back in. Finally, the homeowner will need to make sure that the access points where the bats were coming and going out of are closed up properly and securely. When this process is conducted correctly, a home will not have bats return to turn the attic into their hibernation site again.


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