Bats and Barns

Originally published in the Fall 2003 issue of the Iowa Barn Foundation Magazine.
Written by Bruce Ehresman, Wildlife Diversity Biologist, Iowa Department of Natural Resources.

I grew up on a farm in eastern Iowa (Jones County) and have always held an appreciation for barns. I not only learned the usefulness of barns for the welfare of our different farm animals, but I enjoyed the various kinds of wildlife that inhabited the barns, too. One particular animal that seemed to live in the barn in large numbers was the bat. I especially noticed the bats during the summertime, when I was up in the haymow stacking freshly made hay bales. I would hear squeaking noises coming from the roof rafters above me. Usually, I could not find the animals that were making the sounds, and I assumed that they were hidden in those dark spaces where the sheeting boards were gapped above the roof rafters. But once in awhile, when the hay was piled up high enough for me to get a good look at the barn loft ceiling, I would spot several of the little critters hanging upside down from the ridge rafter at the barn's peak. I remember it being incredibly hot up there, and I was amazed that any warm-blooded creature would choose to be in that spot (if they didn't have to be). It would be many years later before I learned that some bats actually prefer to roost where the temperature exceeds 100 degrees Fahrenheit.

Another thing I remember about those barn bats is that there were a lot of them. In the evening when it was just starting to get dark, the bats would emerge by the hundreds. It was an especially dramatic sight when the large hay mow door was open and the bats could fly out en masse. I grew to appreciate bats on the farm, for I soon learned that they are great catchers of mosquitoes. We didn't have air conditioning in the house when I was younger, and on hot summer nights I often slept out under the stars in our backyard where the air temperature was cooler than inside. As mosquitoes started to buzz about my head, I noticed that bats started to show up too. I soon realized that the bats were feeding on the mosquitoes that were honing in on me. I now know that a bat can eat at least half of its body weight in insects each night. That translates into a lot of mosquitoes!

General Bat Information

Before I go further, I should provide you more information about bats. Bats are a very diverse group of animals and make up about one-fourth of all mammals in the world. Approximately 1,000 species of bats inhabit the earth in a large variety of habitats. There are 45 species of bats in the United States, while only nine species are regularly found in Iowa. Two of these species, the Big Brown Bat and Little Brown Bat, often inhabit buildings, and these are the two bats that you are most likely to find in your barns.

Although many of the tropical bats are fruit and nectar eaters and are important pollinators of such things as bananas, figs, and cashews, Iowa's bats are all insect eaters. The Little Brown Bat, in particular, can eat about 1,200 small insects (including mosquitoes) in an hour, and a nursing mother can eat more than her own body weight nightly. The larger Big Brown Bat eats bigger insects, like beetles, leafhoppers, and moths, and can consume a large volume of agricultural and horticultural insect pests. Just 150 Big Brown Bats can eat so many cucumber beetles each summer that they protect farmers from 33 million of these beetles' root worm larvae, pests that cost American farmers an estimated one billion dollars each year.

Most of bats' insect catching is done on the wing. Even though they can see well, it is their sense of hearing that is most developed and allows them to catch prey in total darkness. While in flight, a bat utters a series of high-pitched squeaks (higher pitched than most humans can hear). These sound waves echo off nearby objects, like barns, tree branches, and insects, and bounce back to the bat's ears into a specialized portion of the brain. This information is processed so fast that it allows the bat to quickly change flight direction to avoid obstacles or catch its darting insect prey.

Bat Biology

While most Iowa bats migrate south in the fall, some spend the winter hibernating in caves (particularly in eastern Iowa). The Big Brown Bat is the only Iowa bat that sometimes is found hibernating in heated buildings, and no bats can survive in places that routinely reach temperatures below freezing. Most bats mate in early fall, just before hibernation, but the female typically will not become pregnant before spring. Young are usually born between late May and late June, soon after females return to their summer roosting areas. Colonial species, like Big and Little Brown Bats, form nurseries of 50 to 1,000 or more individuals in a variety of locations, including tree hollows, under loose tree bark, and in barns and other buildings. The Little Brown Bat has one young each year, and the Big Brown Bat usually has two. Returning mothers recognize their own young within the colony by odor or sound. Young bats grow rapidly and are able to fly at three weeks of age. They become independent of their mothers shortly thereafter and can join the fall migration when less than two months old.

Surprisingly, Little Brown Bats can sometimes be long-lived, reaching an age of 33 or 34 years. The oldest individual known from Iowa was a pregnant Little Brown Bat that was captured at the Manchester Fish Hatchery 23 years after it had been banded (on its wing).

The Value of Barns to Bats

So - how important are barns to Iowa's Big Brown and Little Brown Bats? According to the leading bat protection organization in the world, Bat Conservation International (BCI), the most important threat to bats is loss of roost sites. To my knowledge, no one has quantified barn use by bats in Iowa, but recent studies in other places indicate that barns are very important roost and nursery sites for bats. In one extensive study in Hertfordshire, England, Patty Briggs found that 89% of the barns with suitable roosting features supported bats. As Iowa continues to lose its wonderful old wooden barns, it also is losing valuable homes for bats.

Some of you might now be asking, "Why should we care if bats disappear?" Well, for one thing, they are part of the natural ecosystem in which we both exist. I firmly believe that everything alive exists for a reason, and it seems arrogant of us to assume that we can eliminate species, communities, and even ecosystems without, us or our descendants, experiencing negative repercussions. On the practical side, loss of bats can increase the demand for chemical pesticides, upset natural cycles, and harm human economies.

The argument that bats are harmful because they give humans rabies does not hold water with me. In more than 40 years of record keeping in this country, only 16 people are believed to have died from bat-borne rabies. The chance of dying by lightning strike is far greater than the chance that you will be exposed to rabies from a bat bite.

Getting back to the subject of bats and barns - it seems to me that another good reason for preserving Iowa's barns is to benefit our bats. While building and putting up bat houses is a noble gesture to create homes for bats, preserving a grand old barn that houses the same species that use these bat houses seems an even nobler gesture. And if you want to provide even more homes for bats, you can always attach bat houses to the side of your barn.

Although I still have much to learn about bats, I find that the more I get to know them, the more I appreciate them. I believe that they have their place in nature and that they deserve to be here, too. Perhaps you too will appreciate bats more the next time you notice bats on mosquito patrol in your own backyard or barnyard!

For more information about bats or bat houses, please contact Bat Conservation International, P.O. Box 162603, Austin, Texas 78716.