R.S.Hines DVM PhD 4/21/06 bat house bathouse

Letter to a client:

Good bat house plans are available through Bat Conservation International in Austin, Texas: http://www.batcon.org/.
An excellent publication, Fact Sheets ENY-272 & 268 on the subject is available from the University of Florida’s Cooperative Extension Service, Gainesville, FL, 32611. I generally make my bat houses from 3/8” x 6” Florida cypress planks that I obtain free at a fencing company. They are rough-cut so the bats can scurry up them and need no preservatives. I line them with plastic lanai screen (screen-porch screen) that I staple onto the cedar. A screen or carpet “skirt” hangs below the bottom opening to assist the bats in entering. Be sure that the entrance crack is no wider than ¾ inch, or English sparrows will take up residence. I place them under the eves of existing buildings or on poles that are a minimum of 20’ tall. Others place them in trees.
I currently keep a colony of about 250 Egyptian bats. But I have rehabilitated large numbers of native insect-eating American bats - mostly, free-tailed (Tadarida) and evening bats (Nycticeius), which are the great colony nesters in the Southern United States including Florida. Our Wagner's mastiff bats live farther south than Sarasota - if any are left. The guano for-attraction-idea your Dad was thinking of sounds great but it was tried before on a large scale on the Florida Keys - with no success and by me locally – with no success. I have seeded every conceivable size and shape of bat house with guano and even bats - but this seems to have no effect on whether they stay or leave.

Most homemade, successfully occupied bat houses are raised within 100-700 feet of existing bat colonies. I have moved colonies of several hundred bats to bat houses near their old colony sites by sealing off their entrances into Condominium roofs during the night with “bat exclusion cones”. These are slippery windsock funnels that allow the bats to leave but not re-enter. But when, months later, I transport these vibrant colonies to a new location several miles away (elevated to the same prior height, and in similar shade/sun conditions and north-south alignment) the bats usually only stay for a few weeks and then drift off. No one understands why bats pick one location over another. I am also a beekeeper. With bees, I understand where and why they choose colony locations. Bat, however, are much harder to fathom. I have seen large colonies in the attics of a single house in “cookie-cutter” subdivisions where all houses are identical - yet the bats remain in only one attic and colonies that hover in the attic above a particular condominium and not the ones that adjoin it on either side! Perhaps it is the temperature that the house thermostat is set at or some other unfathomable lure, or perhaps it is a random accident. No one knows. Bat house color seems unimportant. Bats do like a ramp, shelf or shingle roof to land on before scurrying into the hole that leads into the attic, tree or other structure they call home. In the attics, they are never more than one foot farther in than the soffit extension (the load-bearing exterior wall). They do seem to have a preference for acute corners.
It’s my observation, that at the end of the breeding season, a portion of the young bats born that year, look for new nesting sites. This is why all the bats brought to me which have invaded rooms or homes recently are young-of-the-year bats. They can live about 12 years and never seem inclined to move on their own. Some colonies must have alternative roosts because some weeks they do not return to a given location. And then, a few days later, the whole colony is back. Florida Free-tail colonies appear to swell in population in the winter. Perhaps additional bats migrate to these colonies from more northern States. When bat excluders are used, the colony moves to the nearest available nitch. The successful relocation of bats at Gainesville by Mr. Ken Glover, to a specifically dedicated barn-like shingled “house” on telephone poles, occurred only after he had chased them out and sealed all openings on all campus building over a two-year period. Bats are stubborn and perfidious. The closest full-time bat rehabilitator to me is Cindy Marks. You can get her e-mail address from Amanda Loller through her Bat World web-page: http://www.batworld.org . They are located in Mineral Wells Texas. Ms. Loller knows more about hands-on work with colony bats than anyone else in the world. Perhaps she knows some secrets that I don’t that will help your Dad.

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