A Garden and More: Bats Make Great Neighbors!
If you have visited CCUA's Urban Farm at Smith and Fay in the past year, you may have noticed an odd-looking pair of boxes on a pole in the northwest corner of the plot.
The boxes are bat houses. CCUA is trying to lure a colony of bats to the farm. But why?
Why bats need us:
The majority of bats species in the US already have endangered species status or are presently candidates. In Missouri this includes cave-dwelling Gray Bats and Indiana Bats, which use caves, hollow trees, and other sites. The once prevalent Little Brown Bat is also experiencing declines of population. Loss of habitat is a large factor, including disturbances by human beings in caves, the clearing of deadfall logs and hollow trees, and leveling of old barns, sheds and abandoned homes. So creating bat habitat balances an ecosystem suffering from the loss of these insect predators. In addition, hibernating bat populations are suffering the rapid spread of White Nose Syndrome, a disease rooted in fungal infection that can wipe out an entire colony of bats. (Learn more about White Nose Syndrome in this video produced for the USDA Forest Service.) In agricultural areas, heavy use of pesticides on crops reduces the numbers of bats’ natural prey and raises the levels of harmful toxins in bats’ diets. And as the use of wind turbines for power increases, more bats die from collisions with their propellers, which can spin at speeds of over 170 mph – a 2012 study estimates 600,000 bat deaths in addition to birds.
The benefits of bats:
Bats have a fascinating flight pattern, quite different from birds. They are incredibly agile, twisting and turning constantly when feeding, making short lunges and dives to catch mosquitos and other insects, swooping low to drink on the fly from open water, and reversing direction suddenly for landings. The YouTube channel SmarterEveryDay has published a seven minute video that illustrates and explains how different bat flight is from bird flight (and at the closing credits, even shows a bat swimming!). If you already enjoy seeing birds in your garden and other outdoor spaces, you will find bats equally entertaining.
And bats are extremely effective predators of insects, particularly mosquitoes. Over 60% of bats are insectivorous, including most Missouri bats. A single bat eats an average of 1,200 insects per hour, totaling between 6,000 and 8,000 insects in a single night of feeding! Pregnant and nursing bats eat even more, totaling as much as their own body weight in insects every night. Almost all insects moving at night are fair game for bats, including moths, gnats, flies, beetles, and wasps. Many insects eaten by bats are agricultural and garden pests, such as the highly destructive corn earworm moth. And everyone is aware of how unpleasant and dangerous mosquitos can be: we are lucky bats find them so scrumptious!
While small colonies are unlikely to result in a very large quantity of bat droppings, or ‘guano’, what does get dropped over your garden and landscape will be a tremendously effective, long-lasting fertilizer. Both the microbes and the chemical contents (nitrogen, phosphorus, and potassium) are a beneficial byproduct of bats' digestion. But in spite of its history as a valuable fertilizer and its availability as a commercially harvested resource, collecting guano is not recommended for home gardeners. Not only can it be disruptive to the bat colony, but collecting fresh guano also exposes human beings to a kind of spore that can be damaging to the lungs; it is best to just let the benefit fall where it will!
I’m convinced! What should I do to develop bat habitat?
Bat houses need a number of features, not only in their construction but also in placement. Bat Conservation International has published a book on the topic. You can find bat houses for sale as well as bat house plans and placement advice easily online; BatWorld.org provides examples of all of these at one location. You can also find bat houses for sale at local specialty retailers like Songbird Station in Columbia.
Select a site where the house can be placed at least fifteen feet above the ground: bats prefer to begin feeding from a height, and a high roost also provides some protection from certain predators. Bats are hunted by birds of prey like owls and hawks, which can find bats anywhere, but placing the bat house at least twenty feet away from tree branches will minimize their ability to snatch bats just emerging for the evening. In addition, some climbing animals hunt bats, including raccoons, foxes, the occasional cat, and snakes. So when placing a bat house, be sure not to mount it in a place that makes it easy for these predators to gain access to the opening while the bats are resting.
Place your bat house at least fifteen feet above ground level, preferably on a metal or semi-smooth wooden pole or other smooth surface, to foil predators.
Place the house where it will receive at least six hours daily of sun; in Missouri, even full sun all day is acceptable. If you are lucky enough to have females use the house as a nursery, they will need high temperatures in the house to keep the pups warm enough. But choose a place that is not lit with excessive artificial light (like a dusk-to-dawn light) -- contrary to common belief, bats are not blind, and they will prefer an location that doesn't require them to emerge at dusk in a bright area.
Be aware that you are most likely to have success with gaining bat neighbors if you have an open source of water within a mile of the house. Bats drink while flying low over water, so they will prefer areas with a lake or stream nearby rather than a place with only birdbaths within their hunting grounds.
The bat house itself needs several features for the best chance of success:
First, choose or build a house of an appropriate size. Bats prefer to live in large numbers, so aim for a house of a size that will house at least 100-300 individuals. The plans you choose or the labeling of the house you are considering purchasing should make clear how many bats the house will accommodate.
The house should provide an exterior landing area and interior surfaces with a rough texture, grooves, or tacked on screens that the bats can grip with their feet for roosting.
Ventilation is important. Be sure that the house has openings for ventilation and that you install it in a way that leaves the openings unobstructed.
A little brown bat snoozes in a cozy space. photo (c) Wisconsin DNR, located at http://dnr.wi.gov/topic/EndangeredResources/SpeciesPhotos.asp?SpecCode=AMACC01010&PhotoNum=15890
Worries about bats in the neighborhood:
I’ve worked hard to bring birds into my backyard and garden. Will bats compete with my favorite birds?
Because bats are primarily nocturnal, feeding at dusk and overnight, bats do not create competition for birds, even when they are eating the same sorts of insects (as is true with purple martins). Further, since bats enter their roosts from below, crawling up into crevices, under loose bark, or into framed bat houses, they do not compete with birds for nesting sites. Bats even drink water differently from most birds, swooping low over open water and drinking during flight rather than landing in birdbaths. So bird lovers need not worry about the results of bringing bats into the neighborhood.
If I put up a bat house, will bats decide to get into my home instead?
Perhaps, but if you don’t already have bats roosting in your home, adding a bat house is not likely to create that problem. If you do already have bats in your attic or eaves and you want to encourage migration to a more suitable site, either contract a professional or read very carefully about the best time of year and best ways to handle the eviction or 'exclusion' so as not to unintentionally kill the bats involved (especially pups), and be sure to place the new house several weeks in advance.
Will bats bite me (or my pets)? Can they pass on rabies or other illnesses?
Only three species of bats are so-called “vampire” bats, biting their prey and then licking up the droplets of blood that well to the surface. But these species are native to Central and South America, and are not found north of Mexico. And even bats of these species prefer to feed on exposed sleeping mammals, especially livestock; human beings sleeping indoors are usually not their prey. However, as the CDC (Centers for Disease Control) cautions, bats can contract rabies and other viruses. And even non-vampire bats will bite in response to perceived threats, like being captured, entangled, or approached too closely. A bat calmly resting in a low, easily reached space or acting unusual in other ways should be given wide berth, because it may be sick. Direct contact with bats – whether an actual bite or a confused bat colliding with a person – should be followed by medical attention, because bat saliva may carry diseases harmful to human beings. But since less than one percent of bats carry rabies, and since contact or bites with human beings are so rare, the chances of contracting rabies from a bat are extremely low. Especially when balanced with the high number of harmful insects eaten every night, the risks of inviting bats into the neighborhood is quite low!
Where can I find more information?
Besides the links included in this piece, one of the single best online resources for reading more about bats is the 1999 publication on bats by the Natural Resources Conservation Service. The article is slightly outdated in that the number of bat species discovered has increased in the last fifteen years to over 1,200, but the information is otherwise quite accurate and helpful. The Missouri Department of Conservation has also produced a pamphlet, “Missouri Animals of Conservation Concern,” which highlights the cases of Gray Bats and Indiana Bats in our state.