The Use of Bat Houses in the Management of Central Florida Bats

In central Florida, as in other areas, bats often become a nuisance in buildings. The two species most common in central Florida buildings are evening bats (Nycticeius humeralis) and Brazilian free-tailed bats (Tadarida brasiliensis cynocephala). They are often found roosting together. Fortunately, in Florida, bats have some protection as nongame wildlife, and there are no poisons or fumigants registered for use against them. Eviction is the only permanent solution to rid a building of bats, but once they are evicted there is often nowhere for them to go. In most cases the bats will attempt to move into a nearby building that provides a similar roosting area, and the cycle begins again.

As part of my thesis research, I have tested the feasibility of using bat houses as a management tool in situations where bats are to be evicted from a building. If bats would use the bat houses, rather than the buildings, the problem of nuisance bats could be solved.1 In my attempts to get bats to use bat houses, I tried three types of relocations. I "seeded" bat houses with live bats, relocated bats over a period of several days, and relocated an occupied bat house.

I made 13 attempts to "seed" bat houses with live bats. My hope was that bats would remain in the bat houses or at least scent the houses with guano and body oils, which might attract other bats in the future. During the early morning, I captured bats at nearby roosts and placed them in bat houses in groups of 14-115. They were not caged and were free to leave in the evening. None of the seeding experiments resulted in populated bat houses.2

Another relocation attempt was made when bats at a local community college were slated for eviction from the buildings in which they were living. Eight bat houses were placed on the college property, about 1/4 mile from the occupied buildings. Prior to and during eviction, bats were captured at the roost site and placed in the bat houses early in the morning. As in the seeding experiments, bats remained in the bat houses during the day but were free to leave at night. On average, 58 bats were moved each morning and placed in the bat houses in groups of no fewer than six. This process was repeated for eight mornings, but after the third morning we noticed that the bats were already occupying one of the bat houses. The relocation was working! However, within six weeks of occupancy, the plastic ("fiberglass") window screening that lined the roosting spaces deteriorated and began to hang out of the houses. This apparently forced the bats to abandon their new homes. After I removed the screen, we repeated the relocation and bats returned to the bat houses on their own after the second morning. Nearly two years later, six of these bat houses are still populated year-round, each with up to 400 bats.

The third relocation was attempted because bats that had been living in an awning and a nearby bat house were no longer welcome after the building was sold. The tenant removed the awning, which housed a maternity colony of evening bats and free-tails. Between 50 and 75 flightless evening bat pups fell to the ground as the adults flew to the nearby bat house. I was called, and after collecting all the pups I placed them into the bat house in hopes they would be reunited with their moms. However, the tenant now insisted that the bat house be removed from the property.

A few days later we removed the occupied bat house from the building. After we stapled screen mesh to the bottom to prevent the bats from escaping, we moved the bat house to a site roughly five miles to the northeast. Most of the evening bats left the house prior to the move, taking their pups with them. The remaining 10-15 evening bats and more than 100 free-tailed bats with very young (hairless) pups were trans-located. The evening bats were adults and pups old enough to fly. That night adult bats exited to forage, but only the evening bats returned. The free tails had left their pups behind! Thirty-nine freetail pups were in the bat house with 13 evening bats, and the abandoned pups began to starve. Unfortunately, despite rehydration and feeding attempts, only six survived. The evening bats remained at the new site for several months, moving between several additional bat houses I had provided. They left in mid-August, but I anticipate seeing them this year in May.

Bat houses have proven successful as a management tool in central Florida, though much remains to be learned. For example: Where do the evening bats go in late summer and winter, and why? I know they are here year-round, but it is common for them to change roost sites in late summer, returning in the early summer of the following year to form maternity colonies in the bat houses. The free-tailed bats, on the other hand, often stay with the same roost site throughout the year, leaving only on severely cold nights when temperatures drop below freezing.

We hope that land managers and pest control/nuisance wildlife companies will provide bat houses in the future when a roost site is slated for destruction or closure. The bat houses that have proven to be successful in this project are slightly modified versions of BCI’s small and large nursery house designs.

Laura Finn is an Honorary RA in Deltona, Florida. She has been working with bats and bat houses for 8 years, and 18 of her 60 bat houses were occupied in 1996. The techniques she describes pertain to exceptional circumstances, and need not be undertaken in most nuisance bat situations. Wildlife permits and a pre-exposure vaccination for rabies are required prior to capturing and handling bats.