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Bats in our belfry

April 10-12, 1999

Well, actually we don't really have a belfry at the Farmhouse. But you never hear anyone use the term "bats in your attic", or "bats in your carriage house". "Bats in your belfry" just sounds better. 

According to the former tenants, bats have been returning to the Farmhouse every spring for several years. They roost in the attic, the top of the carriage house, in the top of the barn, and in my future den - the little room over the kitchen on the southwest side of the house. They get into this room through holes in the wall, from the carriage house and attic. This room has already been dubbed "the Bat Room" and will probably retain that name so long as we live here, although it might get modified to "Al's Bat Room"

In all these places, the bats have left visible evidence of their stay - accumulations of bat guano were everywhere when we cleaned out the second floor of the carriage house (see previous journal entries - Going to the dump and Carriage House Restoration Begins). We've not yet tackled the clean out of the attic nor the bat room - we're saving some fun chores for later! 

The annual return of the bats to the Farmhouse doesn't evoke the same poetic image of the swallows returning to San Juan Capistrano, or the annual visit of the Monarch butterflies to Santa Cruz. The spring emergence of the black flies and mosquitoes is a seasonal marker in New England, and is also a herald that the bats will soon return. When the food supply appears, the predators will not be far behind. 

All winter the bats have been in hibernation in caves and old mines, mainly in western Maine. Someone tried to draw a parallel between the spring bat migration and the summer migration of tourists to Maine, but it is a little weak, I think. In the first place, tourists don't eat many bugs (at least willingly), and secondly, many of them don't hibernate in caves over winter but can be seen out and about in their winter lairs. And, tourists don't usually foul your attics with their droppings. So, whomever made that negative comparison was probably a bit mean spirited and should be ignored. 

Big Brown Bats and Little Brown Bats

We have two species of brown bats in our area of Maine - the big brown bat (Eptesicus fuscus) and the little brown bat (Myotis lucifugus). Both are insectivorous, consuming 30-50% of their body weight in mosquitoes, moths, spiders, beetles, mayflies, caddis flies and midges every night. The bats scoop up their insect prey in their tail and wing membranes (the patagium) and then transfer them to their mouths. Little brown bats have been observed catching mosquitoes at the rate of 10 per minute, and one bat can catch up to 3,000 mosquitoes in a single evening. Bats use echolocation rather than sight to locate their prey, and hunt for 2 to 3 hours in the early evening. 

Little Brown Bat
photo by Brock Fenton

Little brown bats have a wing span of 6 to 8 inches, are about 3.5 inches long, and weigh about 1/8 to 1/2 ounce. The big brown bat, as the name implies, is slightly longer (4 to 5 inches) and heavier (1/2 to 5/8 ounce). Both bats have glossy brown hair, with dark brown to blackish ears, feet and faces. They have a life span of 18 to 20 years. 

Both species are colonial in nature. In April or May, the females leave their hibernacula in caves and old mines, and migrate to attics and barns for the summer. There they gather in colonies of often several hundred to raise their young. Each female gives birth to one or two babies, usually around the middle of June. After the first day or two when the mother carries them everywhere, the babies are left in the roost each night when the mothers go out to forage. They return to nurse their babies until the young bats start to fly by the age of 18 days. Full growth is reached at 8 weeks. The bats prefer the heat of summertime attics and other building roosts. 

The adult males do not live in the nursery colonies with the females and babies, probably roosting alone or in small groups in cracks and crevices. Early in August, the adult males make nightly visits to the caves and mines that will serve as hibernation sites. As August progresses, more and more adult females and young join the males, and by September the population of hibernating bats builds up at these hibernacula. 

Bat Proofing the Farmhouse

On this trip to the Farmhouse, Paul and I sealed up cracks and crevices under the eaves of the carriage house, holes in the attic walls and eaves, and a big hole at the north peak of the main house, where bats have been coming and going. We wanted to seal off these entrances before the bats returned to their old roosting spots. The holes were covered with hardware cloth, plywood, and/or filled with expandable foam. The loose metal roofing on the carriage house was screwed down. 

Big brown bats only need an opening about 1 1/4 by 1/2 inch to enter a building, and a little brown bat can get through a 5/8 by 7/8 inch hole. We tried to close them all, and will have to see how successful we were when the bats return in a few weeks. 

We want the bats to stay around and help keep the bugs down - we just didn't want to have them spending their summer in the attic! To give the bats a place to roost, we made two large bat houses. 

Paul assembling a bat house
in the office

We used 1x12 pine boards, unplaned on one side to provide a rough surface for the bats to attach to. The boxes are 48 inches tall with three chambers 11x24 inside. They should be large enough for up to 250 bats each. We lined the inside of two of the chambers with hardware cloth to give the bats something additionally secure to hook into when they roost. We made a vertical "landing pad" at the bottom of the box, also covered with hardware cloth, to give them an easy spot to land before entering the bat house. 

One of our unfinished bat houses
showing the roosting chambers

One box was mounted on the north side of the house near the attic, and the other on the east side of the house up at the eaves. Both were mounted about 20 feet off the ground, and well away from any trees or branches.

Wes Smith, from the Maine Pesticide Control Board, came by on Friday (April 16, 1999) to inspect our work and offer advice on how thorough a job we've done. He said that the job to close off entry holes looks OK, but the test will come when the bats return. They will go directly to the entry holes they've used in the past, so there will be no question about whether we've gotten all of them. Paul has taken up an evening bat watch to see when they return.

We mounted one bat box
up under the eaves

Wes also said that we need to move the box on the north side of the house - it is shaded by trees, and won't get enough sun. Mother bats like a hot place for summer roosting and young rearing. Paul will move it to the east side of the barn, on the pasture side, once Derek (Son and wife Jim and Alison's 17 year-old) arrives on Sunday to help with some of the work. Wes suggested that the space we've made for the chambers in the houses is a bit too wide, so Paul will add a third board in the bat house he moves. This will create a fourth chamber, and reduce the chamber widths to about 1 3/4 inches each.

Thank you, Wes, for your time and advice. (I've listed his name at the bottom of this journal entry, if anyone wants to contact him.)

We'll monitor the bats' comings and goings when they return in the next week or two, to see which of the two houses they prefer. If they don't like one, we'll move it in the same orientation as the favored one. After the bats leave for the summer in August/September, we'll stain and seal the houses with two coats of polyurethane, and then remount them. 

For further information on bats, check these sources:

Wes Smith, Maine Pesticides Control Board, 28 State House Street, Augusta, ME 04333-0028, (207) 287-2731. 
Fenton, M.B., Bats Minister of the Environment,Canada. 
Snyder, Ellen, Little Brown Bat, UNH Cooperative Extension. 
Bat Research,Oregon Public Broadcasting. 
The truth...about bat boxes, Quest Solutions. 
Bats in buildingsUniversity of Florida. 

In other updates on the restoration, Paul finished the steps and ramp to the entryway. He replaced the siding so the whole south face of the carriage house now looks real fine. The shipping room is next. I've also gotten bids for installing a whole house cable system for the phones, LAN and video systems - that'll be sometime in the next month or so if I can work out the details. 

Allen and Penny Crabtree

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Last updated April 17, 1999