Photograph by Scott Altenbach
Endangered species found roosting in OBC bat house!
by Susan Christiansen-Trokey

It all started about six years ago, when I first met Cyndi Marks at a program she was conducting at the Sanibel-Captiva Conservation Foundation. At the end of the evening, she allowed me to spend more time with a big brown bat named Charlotte. When the bat began to purr, I knew I was hooked.

About 4 years ago I got an OBC bat house from the Florida Bat Center, and my husband Greg put it up in our yard, after a bat had moved into our woodpecker house. He placed the house on a 16' 4X4 with a metal pole extension to raise the base of the house 17' high. He added approximately 4 feet of flashing to prevent predators from entering the house. The house was faced in a south/south/easterly direction with a small lake directly behind the house.

Almost immediately bats moved in. That year we had about 20 bats. The following year over 70 bats were living in our single-chambered bat house.

The major nightly event at our home was watching the bats come out in the evening and then return just before sunrise. We loved sitting out at night and really enjoyed that we were never bothered by mosquitoes. However, by August the number of bats began to decline, and by September all of them had left. Our family really missed watching the bats and worried about them. Cyndi told us that we probably had a maternity roost that year, and that really excited us to know that we may have played a small role in helping the bat population of SW Florida. To our dismay, there were no bats in our bat house last year. Unfortunately, we had lots of mosquitoes (not a good thing with the advent of West Nile disease in Florida).

In February of this year, my 16-year-old son, Victor Young, began hearing bats and then noticed them flying out of the bat house one evening. The bats looked a little bigger than the previous bats and one of them appeared to be white. We asked Cyndi and George to come to the house to identify what species we had. They came over with the hope that these large bats could be Wagner’s mastiff bats, a state listed endangered species. They set up their Anabat system, a computerized bat detector, and were able to tell us that we had some Brazilian free-tailed bats and several other "unrecognizable" bats. The calls seemed too high in frequency to be mastiff bats. Several weeks later they came back, this time with a mist net to catch and identify the mystery bats. Somehow the first bat made it over or around the net, but the second one was trapped moments later, just as I heard George say, "That was low," meaning the frequency at which the bat was echolocating. Almost immediately I heard Cyndi say, "You have the endangered bat." While Cyndi was removing the bat from the net, George lowered it so that no more would be trapped. Once out of the net, we got to get a good look at it. It was a rather large compared to other Florida bats, with big ears, brown fur and a white underbelly. We took measurements, photographed the bat and released it, recording its calls as it flew away.

It thrilled us all to have found this species living in our bat house, especially since it had been sighted in Florida only a handful of times in the past 20 years, with none of the sightings being in a bat house. I later learned that the U. S. Fish and Wildlife Service had recently commissioned a study to determine the status of these bats, and since I work for the Service, I contacted Laura Finn of Fly-by-Night, Inc., the organization performing the study. Laura and her assistant Kelli also came to our home and together with George and Cyndi recorded the bats with their Anabat systems and on night vision video cameras.

We are still seeing the white bat, but have realized that it is not merely white on the belly, it is completely white, wings and all. We do not want to attempt netting it since it is now maternity season and we do not want the bats feeling that our home is not a safe place for them to raise their young.

It will be a truly unique find if we not only have state endangered bats living in the house, but have an albino one as well. I plan to keep everyone posted as we learn more about this endangered species.

Year-by-year details of the OBC bat house occupancy

2000: An OBC single chamber bat house was erected on a 4 by 4 wooden pole, with a metal extension, making it a total of 17 feet high. Four feet of flashing was attached to prevent predation. The bat house faced southeast with a small lake approximately 20 feet in the rear. This single chamber bat house measures 24 inches high by 14 inches wide and is 1 1/2 inches deep. The total roosting space inside the bat house is 16 inches by 12 inches. The bat house has a predator guard, creating an opening of 3/4 of an inch for the bats to enter.

2000: One month after the OBC bat house was positioned, approximately 20 bats, probably Brazilian free-tailed bats (Tadarida brasiliensis), occupied the house.

2001: 70 bats found living in the OBC single chamber bat house.

2002: Bat house vacated.

2003: In February, bats were again observed flying out of the bat house. Owner noticed the bats looked larger than the previous residents, and included an albino bat. These bats were identified as the Florida bonneted bat. Twelve bonneted bats, including the albino, were documented. Owner then placed up an OBC triple celled bat house measuring 24 inches high, 14 inches wide, with a 12 by 12 inch interior. The triple chamber bat house has roosting chambers of 3/4 to 7/8 of an inch. Brazilian free-tailed bats immediately occupied the triple celled bat house.

2004: Brazilian free-tailed bats moved out of the triple chambered bat house. Florida bonneted bats still occupied the single
chamber.

2005: The triple chamber bat house was taken down and a second OBC single chamber bat house was placed up. That spring the
second OBC bat house was found to house several Florida bonneted bats. The albino bat has been seen regularly at the bat house since 2003.

2005: This summer, the total number of bats that occupied the two bat houses ranged from14 to 16, including at least three young.

Background on the Florida bonneted bat

The Florida bonneted bat (Eumops floridanus), formally known as the Wagner’s mastiff bat (Eumops glaucinus floridanus), is an endangered species found in the southern portion of the Florida peninsula.

This species has rarely been observed over the past four decades, with no roosts reported since 1979.

A colony consisting of at least one male and several females has taken up residence in a bat house in a North Fort Myers, FL (Lee County) suburban backyard. The colony moved into a single chamber bat house, built by the Organization for Bat Conservation (OBC), in December 2002. This is the first record of Eumops floridanus using bat houses. Other bat house styles have been tested over the last three years and none have successfully attracted the Florida bonneted bat.

The colony has ranged from 8 to 14 individuals, including an albino. Offspring have been observed in the roost. The colony has maintaned constant residence in the bat house through major Florida storms, including Hurricane Charley in 2004.