Now that you are an expert on bat houses, please see our bat house shoot out. Make sure any box you consider for purchase or build as a kit is certified by the North American Bat House Research Project, part of Bat Conservation International!
This bat house at the left is large, which is good. Bats seem to like larger structures over tiny "bird house sized" boxes being offered today in hardware, nature, garden, and science stores. Though large, this box with it's 1''-2'' interior baffle spacing (too wide), lack of landing plate, and shady placement on a tree all contribute to it's failure. This box can be upgraded to a degree with the addition of a landing plate, a fresh round of sealant, and a sunny location. The fixing the all-important interior crevices would require total disassembly, time better spent creating a new box with a new design.
All bat houses are not created equal
Few box manufacturers promote their products with photographs of bats actually using their boxes. While it is a little tricky to get great shots of bats in or emerging from bat houses, more likely the problem lies with bats simply refusing to use them. Fortunately with the invention of the internet, it is now possible to compare proven products with those that are more intended for decoration.
Bat houses found in most shopping mall nature stores, mail order catalogs, nationwide hardware stores, and birdhouse websites may be from antiquated plans. Usually they are designed to be fast and inexpensive to make. For several years now we have been teaching the bat house building segment at the annual BCI Bat Conservation and Management Pennsylvania Workshop. Participants are always surprised to learn all the details that go into a successful bat house. We teach that bat houses will fail because of three reasons:
Common bat house design and construction problems
Bad bat house designs are simply flawed from the start. They are often too small overall and contain crevices too large. Sometimes a critical detail is omitted, such as a landing plate. Usually these boxes cannot compete with a modern design, even after being upgraded by a creative hobbyist. Bad construction is a different matter, usually the box can be successful after some paint, caulk, extra screws, and extra roughening.
One of many experimental bat boxes built in Pennsylvania. This design is mildly successful but can get too hot internally due to the lack of overall height of the box. The bottom door must be kept closed to keep stray light from driving off bats. This same door allows guano and parasites to build up. Tall, open bottom BCM boxes give bats a temperature gradient and are self-cleaning.
Common placement mistakes
The greatest bat house in the world will never contain a bat unless it is placed properly in the field. In cool climates it is best to avoid shady locations at all costs. Often this limits the mounting options to strategically placed new posts or sunny chimneys. Bad placement includes the following:
Why do Some Bat Houses Fail?
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