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House Bat Management


Artificial Bat Roosts

If batproofing is effective bats will be displaced and the excluded colony will reestablish in an alternate roost. If none is available will the bats utilize artificial roosts?

Alternate Roosts

The following incident described by Cope (1959) will illustrate the vagaries of batproofing and poses the question of where do dispossessed bats go:

A friend has been studying the life history of bats and was anxious to set up a breeding colony in the attic of his garage. Because a breeding colony of bats (species not mentioned) in the neighborhood was about to be destroyed, a duplicate of the habitat of this colony was made by my friend - the rafters designed the same, the opening was similar, and some bat guano was even put on the floor. Then about 50 bats were liberated from the established colony into this artificial colony. The bats at first seemed quite at home. They clung to the rafters and found crawl spaces and hideaway places. The bats were liberated in the daytime; the next day not one bat was back at the new location. But in the old location were many bats which had been liberated in the new one. In a week or so, a second roof was built and all cracks and crannies were blocked off so the bats could not get into the house. Then and only then, they were forced to abandon the long-established breeding site. Did they go to the new colony established a short distance from the old site? No. Where they moved, no one knows.

It is known that bats have alternate roosts, which is probably where they go according to D. G. Constantine (personal communication). M. D. Tuttle (personal communication), in agreement, believes that bats require a nearby foraging habitat as well.

Bat Towers

The usefulness of bats as insect feeders and the value of their guano led to several attempts to encourage Mexican free-tailed bats to occupy artificial bat towers (Greenhall and Paradiso 1968: Fig. 3. Campbell (1925) spent his life working on such a structure. He built a tower but the bats living in an old hunting lodge a few miles away refused to move into the tower. Campbell reasoned that the bats depended on their delicate sense of hearing and perhaps some sounds would have a repellent effect. A brass band with cornets, clarinets, piccolos, axophones, trombones, drums, and cymbals, provided a variety of noises. Finally, Campbell found that the only music the bats could not stand was the waltz, "Cascade of Roses," as played by the Mexico City Police Band. He wrote: "With the sound of the very first measures, a great uneasiness and shifting of the bats was observed, but with the first fortissimo, they began leaving; first in singles, then pairs, then tens and hundreds in one continual stream, until they had all left. Their time of emergence in that month, August, was always about 6:30 o'clock; now they left one and a half hours before their accustomed time." The bats moved into the tower and during the following 6 years, never returned to their old home. The strategy was successfully repeated when a clergyman wished to get rid of some bats lodging in his room. Having heard of the "concert" experiment, he purchased a phonograph, a few records, and won the battle in 1 day.

The fact that the artificial roost was satisfactory warrants further study. R. A. Raschig, inspired by Campbell's efforts, built a bat tower in Eagle River, Wisconsin, which attracted bats (personal communication). In the fall of 1979 a woman "saw bats come out of the roost by the hundreds. I have not seen a permanent colony but have reason to believe that the bats use this roost as a stopping off place in their migrations in the spring and fall. At times there are hawks and owls roosting on top of the bat roost presumably waiting to get a dinner when the bats emerge."

Bat Houses or Boxes

During the past 50 years the natural holes in trees have been reduced in numbers by removal of dead and dying trees which provided cavities for many animals, including bats. In Europe bird boxes have been used for about a century. Since the late 1930's, European bat biologists have provided a variety of boxes and houses for bats. The success of these artificial bat roosts has encouraged English and American investigators to experiment further (Fig. 17). The English bat biologist, Stebbings (1974), stated that "Although insufficient knowledge is known about the critical roost requirements of bats, they can be attracted to roosting boxes attached to trees. These boxes simulate tree holes (like bird boxes) and can be used by large numbers of bats of most species. One box of about 10 cm cube can hold up to 50 bats." Krzanowski (1955) has had excellent results with bat boxes in Poland.

Since the use of bat houses or boxes is new in the United States there is much to be learned. The two models (Fig. 21) have been used successfully in Europe. Suggestions for building bat houses and attracting bats are provided by Tuttle (n. d.). Size and shape do not appear important but the width of the entry space should not exceed 2.5 cm (1 in.). All inner surfaces must be roughened so that the bats can easily climb. Because inside house temperatures should not exceed 32° C (90° F) the box should be insulated by covering the top and sides with tarpaper, styrofoam, or even painted black to absorb the heat from the sun and provide a suitable temperature at night, especially for a maternity colony. Bat houses should be securely fastened to the side of a building or tree trunk 3-5 m (12-15 ft) above the ground and protected against birds and squirrels.

GIF -- Bat houses.
Fig. 21.  European bat houses. (Courtesy of Merlin D. Tuttle)

Food supplies must be adequate and bat boxes should be located near some water where insect populations are abundant. Sometimes a bat house may be occupied within weeks after it is erected, preferably by early April, or it may take a year or more for bats to find, approve, and move into a bat house. A well-insulated box located near water, securely fastened, and protected against wind, predators, and direct sunlight increases the chances of early occupancy.

The Missouri Department of Conservation reported that some private citizens designed and built a large structure called a "bat refuge" (Fig. 22) that was attractive to little brown bats and quickly occupied (LaVal and LaVal 1980). This artificial bat roost is located at Tea Lakes Wildlife Area, near Rosebud, Gasconade County. It was erected during the spring of 1979 and was used later by a maternity colony of at least 78 little brown bats during the summer of 1979. The colony originally occupied a picnic shelter close to where the artificial roost was built (note the picnic shelter in the background of the photograph). The picnic shelter caretaker gradually stopped up holes and cracks to encourage the bats to move. It is not known why the bats moved but it is believed that they were possibly attracted to the refuge by spraying it with a guano solution. R. K. LaVal (personal communication) suggested that the roost (Fig. 23) be modified by reducing the spaces at the bottom between the dividers to less than 2.5 cm (1 in.), making slit openings into the air space under the roof which should make the roost more suitable for maternity use by the bats, and by raising the structure to reduce disturbance from people, dogs, and other organisms.

JPG -- An Artificial bat roost.
Fig. 22.  Artificial bat roost built by private citizens at Tea Lakes Wildlife Refuge Area near Rosebud, Missouri. (Photo by Richard K. LaVal)

JPG -- An Artificial bat refuge.
Fig. 23.  Artificial bat refuge (bottom) at Tea Lakes Wildlife Area near Rosebud, Missouri. (Photo by Richard K. LaVal)

Plans based on this successful but experimental bat house were developed by the Missouri Department of Conservation (G. T. Maupin, personal communication). The Department is currently implementing plans to design, build, and field test additional bat refuge structures, to be able to offer a viable alternative to the extermination or exclusion problem of bats in buildings (LaVal and LaVal 1980).

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