BROADCASTER ARCHIVES

Bats on your Farm: The Benefits of Order Chiroptera
By Heather Kaarakka

This article was printed in the May/June 2010 issue of the Organic Broadcaster, published by the Midwest Organic and Sustainable Education Service.

Spring means growing season is starting and the field work begins, but it also means the return of the bats. Bats in the Midwest have either been hibernating or overwintering in the south, and the return of warm weather and long days brings the bats out of hibernation to do what they do best: eat insects.

Bats have been feared for many centuries because of myths and misunderstandings, but in recent years researchers have shown bats to be an integral part of almost every ecosystem. There are over 1,100 species of bats in the world, and 45 in the United States. Most of the bats in the US are insect eaters and use echolocation to navigate and capture prey. Bats are members of the order Chiroptera, not rodents as many people think. They have slow population growth rates because they usually only give birth to one young per year, and they have some of the longest life spans for a mammal of their size: some bats live to be over 20 years old.

As many organic growers are already aware, bats can be an amazing form of organic pest control. A single little brown bat can catch and eat 1,200 mosquitoes sized insect in one hour, and a nursing mother can eat more than her own body weight, up to 4,500 insects in a single night! 1 But bats don’t stop at mosquitoes. Most bats are generalists, and will eat anything from moths to flies to beetles, including agricultural pests such as rootworm, cutworm, earworm and leafhoppers. A colony of 150 big brown bats can protect local farmers from 33 million rootworms each summer 2.  Bats are so efficient that one researcher estimated that Brazilian free-tailed bats in the southwest prevented 1-2 pesticide applications per year resulting in a savings of $100,000 per 4000 ha of farmland 3. Not only do bats perform pest control by simply eating insects, it is apparent that their presence also has an effect on insects in the area. It has been documented that moths often listen for bat echolocation and will avoid an area if they hear bat calls 4.

A farmer in Oregon all but eliminated his use of pesticides by attracting bats and birds. By building suitable bat houses and mounting them in the correct place, he encouraged 600 bats to take up residence on his farm, and went from spraying pesticides 13 times a year to only twice after the birds and bats leave in the fall 5.

Putting up bat boxes or other roost structures is a great way to encourage bats to take up residence and reap the benefits of having them in your area. Depending on where you live, you may get the little brown bat, the big brown bat, the evening bat, or the endangered Indiana bat residing in your bat boxes. Research has shown that organically managed farms support higher levels of biodiversity, including high diversity of bats, so your farms will likely get several species of bats. Other bat species that may visit your farm, but not necessarily live on it, are the northern long-eared bat, the hoary bat, the red bat, the silver bat and the Eastern pipistrelle. These bats prefer to roost in trees, but love to visit farms with all sorts of prey items to eat. By farming organically you are encouraging multiple species of bats to feed on your agricultural pests.

After you start getting bats roosting in your bat boxes, harvest the guano and use it as a fertilizer; plants love it. Its chemical content has been reported to be 10% nitrogen, 3% phosphorus and 1% potassium 6. This is a great combination, benefiting all sorts of plants. Bat guano is good at rebuilding soil, and it doesn’t leach out of the soil as fast as artificial fertilizers 7.

Unfortunately, like many animals in the US, bats are becoming endangered at an alarming rate. In 2006 an unprecedented disease called White-Nose Syndrome was discovered to affect bats in the Northeastern states as they hibernate in winter. It is caused by a fungus called Geomyces destructans and has a mortality rate of 90-100% in infected hibernacula. It is currently spreading south and west, and could reach the Midwest in as little as a year. It is not yet clear how the fungus kills the bats, but it is apparent that it wakes them from torpor causing them to burn valuable fat reserves as they wake.

Little research has been done to assess the impact of an area experiencing a 90% reduction in bat pest control in a single year, but it is possible there will be a sharp increase in spending to combat agricultural pests in the years following a drastic drop in bat population.   

In response to this devastating disease, Wisconsin Department of Natural Resources has created a Bat Roost Monitoring Program in an effort to monitor known bat roosts in Wisconsin and the Midwest region. From the data collected, research scientist from the DNR’s Endangered Resources program are creating baseline inventories of species distribution, counts of bats roosting, and phenology of when the bats return and leave the roosts in the spring and fall before White Nose Syndrome occurs in the area.

Wisconsin Department of Natural Resources Bat Monitoring Program is sending out a call for the locations of known roosting sites. These may be bat boxes, old buildings, bridges, or other man-made structures. If your farm has bats roosting in it, we would like to know, especially if you live in Wisconsin. If you are not aware of any bats roosting on your property, but would like to provide roost opportunities for attracting bats to your area, installing an appropriately designed bat house is a great way to encourage them. Bats like specific designs of houses mounted in sunny south-facing sites.

Contact John Paul White: John.White@wisconsin.gov or Heather Kaarakka: Heather.Kaarakka@wisconsin.gov of the Wisconsin Bat Monitoring Program for more information on bat houses, and to report roosting sites.

Citations
1, 2. Bat Conservation International. www.batcon.org. 2010
3. Cleveland et al. 2006. Economic Value of the Pest Control Service Provided by Brazilian Free-tailed Bats in South-central Texas. Front Ecol Environ 4(5): 238-243.
4. Kiser, M., S. Kiser. 2002. Bat Houses for Integrated Pest Management Benefits for Bats and Organic Farmers: Phase I. Organic Farming Research Foundation: Santa Cruz, Ca.
5. Murphy, M. 1993. Bats: A Farmer’s Best Friend. Bats 11(1).
6,7. Keleher, S. 1996. Guano: Bat’s Gift to Gardeners. Bats 14(1).

Heather Kaarakka works for the Wisconsin Bat Monitoring Program of Wisconsin Department of Natural Resources.