In permaculture, we look for opportunities to expand on biodiversity, as well as take advantage of functions that can occur naturally or with minimal inputs from us. While often this takes the form of rotationally grazing domesticated animals, including them in waste cycles, and using them for pest control (a la not a slug problem but a duck shortage), we are also inclined to make the most of wild fauna as well.
Utilizing wildlife happens in many ways. We create good habitat for predatory insects with piles of logs and layers of mulch, for frogs with small ponds, for lizards and snakes with rockeries, and for birds with hedges. We attract bees and butterflies with particular flowers. We cultivate populations of earthworms and black soldier flies. In return, they control pest populations, add fertility, spread seeds, and create compost.
Why Bats Are So Useful
Bats, too, are wonderfully useful wildlife. In fact, their collective functional value is quite high when compared to other animals.
Like predatory insects, frogs, and lizards, some bats are skillful pest eliminators, and this is particularly useful in that they are doing it in the air (rather than relatively stationary) and at night, when other animals are often sleeping. They are also particularly linked to eating pests that are problematic for crop favorites, like corn, tomatoes, and beans, to name but a few.
Like birds, bats are founts (for want of a perfect word) of fertility, and some of them, also like birds, are great cultivators of seeds. Guano is used in many product fertilizers and is likely the most profitable of all animal excrement. Obviously, as is the case with birds, when bats eat fruit and dispose of the seeds, they do so in beautiful capsules of richness, helping new fruit plants get their start.
Like bees and butterflies, other bats are actually pollinators, known to consummate the love of over 700 plants, such as mangoes and avocadoes. These bats are nectar-eaters, and they dart around from flower to flower, spreading pollen as they feed, much the same way bees and butterflies do.
As is now apparent, bats bring a huge element of biodiversity to a farm as well. Not only are they a productive animal to the ecosystem, often filling nighttime niches that other animals won’t, but also they are the second largest (rodents are first) mammalian families, with over 1300 species. Different species of bats, too, are very different in their habits, as some hunt down insects, others—the biggest—eat fruit, and still others pollinate. Luckily for us, just about any permaculture site would likely provide for bats, and they undoubtedly would pay that favor back to the farm.
Where Bats Like to Be
When working in Panama, I was trimming some banana leaves down to allow some sunlight into an area, and as I passed through with my machete ablaze, I whacked the wrong leaf. Suddenly, in mid-morning, five or six bats were circling in the understory until finally settling back, again as a group, under a new leaf. From then on, I would see them daily, huddled on the underside of banana leaves. It’s the perfect bat home.
Funnily enough, at the same site, we later discovered a small group of bats that would spend their days on the underside of a mango tree, which again makes perfect sense for a bat hangout. In the evening, these bats would spread out over the two acres and beyond, but during the day, they would cuddle up and hang out high in the shade.
Prior to that, I’d known bats as somewhat problematic fruit eaters. I’d worked on a farm in Guatemala where they’d munch down on the occasional bunch of bananas growing, and more so, they’d leave little marks on the avocadoes. On that same farm, I watched the owner gleefully show off a pile of guano when he discovered some bats living under the siding, on the sun-facing side, near the top of his A-frame house. Again, it was the perfect bat home.
While we often think of caves, bats live in many places. We also find them under the eaves of our houses and in the crevices of buildings. They are particular, like most animals, to specific conditions. They like the darkness, and they like tight spaces, such as perched along the spine of huge banana leaf. They like to be high and safe from predators, such as on the underside of a huge mango tree with tufts of leaves obscuring them. They like to be warm, such as under the siding of a house being bathed in sunlight. These are natural conditions that might attract bats to your garden.
How Bat Houses Work
The other option, perhaps a tad more accommodating, would be making bat houses, and those can come with some extra perks, too.
Bat houses are simple to build. More or less, they are thin boxes, about 60 centimeters by 60 centimeters but only about two centimeters deep. They need a good roof, and the box itself should be sealed except for the bottom. The back panel of the box should be a little longer (reaching about 5-10 cm lower) than the front panel, giving bats a landing platform, and reaching a little higher than the front panel, giving the roof a pitch. The back panel should also have enough texture for bats to get traction for climbing in. Low on the front panel, especially in warmer climates, some ventilation is good, either about a one centimeter slit or a line of drilled holes about ten centimeters from the bottom.
Once the box is put together, it needs to mounted onto something that is high and steady, such as a tree, post, or wall. The recommended height for bat houses is about four to five meters high, in order to keep them safe from predators. Additionally, and somewhat surprisingly, the boxes should be placed in a sunny spot, not for the light but for the warmth. If there are plenty of posts or scrap boards around, those can be used to place bat houses exactly where you want them. Then, it’s a waiting game, but if bats are around (and they usually are), they will find the boxes. (Obviously, different species will have different preferences, so a little research may go a long way in attract the right bats.)
While there are many designs and considerations for bat houses, including large-scale domed roofs that could double as shelter for straw or something else that needs to be kept dry, the basic box described above can most likely be put together with scrap material or a repurposed pallet. Multiple boxes can also be mounted around the garden, and these can double as strategically placed nutrient deposits, knowing that guano will drop below the houses. The guano can either be caught in a well-placed container to be used where needed, or there can be garden beds or irrigation ponds catching it below, spreading the nutrient with no additional effort required.
Header: Bracken Cave Bats (Courtesy of Daniel Spiess)