Bat Houses and Placement Strategies

I have invested a fair amount of time researching bats the last month or so trying to learn more about the fascinating creatures sharing my yard this summer.

After last week’s blog about my recent success with bats a few customers had questions.

One customer asked “why do you think you have more bats this year. What did you do to encourage them”? The fact is I’ve done nothing different and I wish I knew why we have this surge in numbers. The bat house has been in the same place for several years. The only thing about the “Rocket” style house that’s different is Downy woodpeckers have pecked a couple of holes in it ranging in size from about 1 ½” to 3” in diameter. I hardly think that would increase the chances of a box being used.

Bats have to find new roosts on their own. They investigate new roosting opportunities while foraging at night, and they are expert at detecting crevices, cracks, and nooks and crannies that offer shelter from the elements and predators. Bats are not blind as the saying goes but in fact have sharp eye sight.

BCI (Bat Conservation International) indicates 90 percent of occupied bat houses were used within two years (with 50 percent occupancy in the first year). The rest needed three to five years for bats to move in. So, perhaps it was just time needed for bats to locate my house. Now that I’ve attracted bats to this house I am planning on putting up at least one more before next spring.

There's a lot of information about success rates of various types of bat houses and, perhaps more importantly, how they are presented. I am merely going to summarize some of the more pertinent information and would encourage you to visit www.batcon.org if you want to learn more or have enough interest to construct, or buy, a bat house to install in your yard.

Below are some basics of presenting a bat house.

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Three chamber bat house.

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Rocket style bat house.

Facts, Tips and Suggestions

Bat houses installed on buildings or poles are easier for bats to locate, have greater occupancy rates and are occupied two and a half times faster than those mounted on trees.

Tall designs like the multi-chamber (nursery) and rocket-style houses perform best

Occupancy in rural areas is over 60 percent, compared to 50 percent for urban and suburban areas.

According to BCI maintaining proper roost temperatures is probably the single most important factor for a successful bat house. They say interior temperatures should be warm and as stable as possible (ideally 80º F to 100º F in summer) for mother bats to raise their young. Some species, such as the Big Brown bat, prefer temperatures below 95º F, while others, such as the Little Brown bat, tolerate temperatures in excess of 100º F. This is very interesting because we always think of bats in relation to the coolness of caves but this is mostly during the hibernation months, fall through winter.

Bat house temperatures are influenced directly by the exterior color and direction faced. East-, southeast-, or south-facing are generally good bets. My Rocket house is, as you have seen, a darker color. Bat houses we sell are almost always a plain western cedar. From now on I will suggest staining the box a darker color.

Avoid placing bat houses directly above windows, doors, decks or walkways. Bat urine and guano would fall directly down to whatever is below. The urine is known to stain some finishes.

For more information about constructing, painting, installing and maintaining your bat house, please see:

The Bat House Builder's Handbook

Single chamber bat house plans

Four-chamber nursery house plans

Rocket box bat house plans

My Summer Bats

Bats have been of particular interest to me this summer as I’ve had great success with a “Rocket” style bat house. This box has been on a 10’ post in my yard for several years and seen only minimal success.

Most evenings my wife and I settle in to watch the bats emerge from the box which is situated in a clearing surrounded by trees. We’ve been able to count over one hundred several times. Only recently have I come to the conclusion they are the species, the Little Brown Bat, perhaps the most common, widely distributed in the U.S. They measure less than 4” in length and vary in color from olive-brown to a yellow-brown. The wings consist of naked skin, which are attached alongside the feet.

There are several bat species that are very similar in appearance, so we are still observing for more details and clues that will help definitively identify them.

During summer Little Browns often inhabit buildings, usually in hot environments like attics, where females form nursing colonies of hundreds or even thousands of individuals. Not much is known about where the males are at this time but they are likely solitary and scattered in a variety of roost situations. Colonies are often close to a lake or stream. This species seems to prefer to forage over water, but also forages among trees in open areas. Little Browns may repeat a set hunting pattern around houses or trees. Little Brown bats eat a variety of insects, including gnats, crane flies, beetles, wasps, and moths. Here is a very interesting thing I did not know about bats. Insects are usually captured with a wing tip, transferred into a scoop formed by the forwardly curled tail, and then grasped with the teeth. Because we don’t get to see them working in slow motion we would never see this action.

After doing a little more research on Southeastern bats, I learned some very interesting facts about these fascinating little nocturnal mammals. For instance, did you know that at certain times of the year we can have up to fifteen different species of bats in the southeastern United States? Or that all bats in the eastern United States feed exclusively on insects? They are the only major predator of night flying insects and may eat more than 50% of their body weight each night. Unfortunately, the amount of mosquitos they consume is not as great as once thought.

In late fall and winter the Little Brown Bat usually hibernates in caves and mines. Bats return from migration and awaken from hibernation as early as mid-March and they will be abundant throughout the summer and into early fall. By mid-October most will have migrated to more southerly states, or are going into hibernation. For more information about bats in our area please visit: www.tnbwg.org the Tennessee Bat Working Group website.