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Bats of South Florida1
Frank J. Mazzotti and Laura A. Brandt2Background
Bats, like snakes, sharks and spiders, seem to evoke feelings of fear and loathing beyond the harm that they may cause people. Bats are especially harmless; being primarily insect, fruit or nectar eaters. In reality, bats are very shy and not at all aggressive. It is true that many photographs of bats depict a snarling, grimacing expression; however, we guarantee that most humans, prodded awake and harassed with bright lights, would not respond more graciously.Bats are the only flying (rather than gliding as "flying" squirrels do) mammal. Their flight is characterized by wonderful acrobatics as they dip and dart after their insect prey. The most notable structures of a bat are its wings, which are essentially the same as our arms and hands, thus the scientific name Chiroptera or handwing. ( Figure 1 ). The bones of the hand and finger are elongated and serve to support and move the wing. The hind limbs of bats are modified for landing and hanging upside-down.
Figure 1. Major external features of the big brown bat (Eptesicus fuscus). Description
Habitat
Bats are common throughout the United States. Five species from 2 families of bat occur in South Florida (Table 1 ). Most species of bat are more abundant in northern counties (there also are more species in northern counties). They are most frequently observed on warm evenings; feeding over bodies of water, along buildings or forest edges, or around lights. Many species are attracted by water, and a quick stop for a drink after emerging from a roost is a common behavior. In the daytime bats seek shelter in a wide variety of dark, secluded places.Roosts can be found in buildings, caves, crevices and even in the foliage and branches of trees. In south Florida tree cavities, snags, and especially unpruned cabbage palm trees are important roost sites. Window shutters, drain pipes, billboards, and various other nooks and crannies also house bats.
During the day the body temperature of bats approaches that of the surrounding environment, and their metabolism is at a reduced level. Bats are relatively inactive during periods of cool temperatures, but on warm days the entire group may be noisy and active. As evening approaches bats become more active and vocal, leaving the roost shortly after dark.
Diet
After their evening drink, taken in flight, bats feed for about an hour or so; resting once their stomachs are filled. They may feed again just before dawn, returning to their roost by daybreak or shortly after.Around the world bats feed on many types of food: insects, blood, fish, mice, lizards, fruit and nectar. All Florida bats eat insects. Bats locate flying insects with a sophisticated sonar system (echolocation). They emit supersonic sounds and listen for echoes indicating prey. Insects are captured with the mouth, wings and tail membrane. Bats can eat small insects in flight, but must land to devour large ones.
Offspring
Although most bat species mate during the fall or winter, fertilization does not take place until spring with birth occurring in late spring or summer. The litter size is usually one or two young. Most species gather in nursery colonies. Very young bats remain attached to the female during the day, but are left behind when the female leaves to feed at night. Mothers periodically return during the night to nurse their young. Most bats can fly when they are three weeks old. As they learn to obtain their own food and become less dependent on the mother, the nursery colonies disperse.Hibernation
Most bats hibernate during cold weather. In south Florida bats become less active during the dry season (December to April or May), not only as a result of cooler weather, but also because of low food (insect) supply. Bats survive these periods of low activity by using deposits of fat stored when food was abundant.Costs and Benefits of Bats
Bats suffer from bad public relations. Everyone is familiar with Hollywood's portrayal of huge vampire bats sucking blood from the necks of young women. Aside from movie directors using rubber bats the size of small hang-gliders, the directors also are inaccurate about their feeding location and feeding method.Vampire bats are mis-portrayed. Of the three species of vampire bat none are the size of small hang-gliders, all inhabit Central America, and they all feed by lapping the blood from small incisions made with their teeth. And, the vampire bats' prey, usually livestock, hardly seems to notice the little mammal licking at its fetlocks.
Bats are more helpful to humans than harmful. A single bat can eat thousands of insects each night. Fruit-eating bats are essential for dispersal of seeds in tropical forests, and nectar eating bats are necessary for the pollination of countless tropical plants. In some countries bat guano (feces) is a valuable fertilizer.
Bats are not prominent disease carriers. One of the most widespread misconceptions about bats is that they commonly carry diseases, especially rabies. Only a fraction of one percent of bats have rabies, and infected bats very seldom become aggressive as other mammals do. You are more likely to die from food poisoning contracted at a church picnic than from getting rabies from a bat. Learn to leave bats alone; they will return the favor.
The genuine nuisance. A genuine nuisance occurs when bats roost in large numbers in human dwellings. The rapid and smelly accumulation of guano is unpleasant, and any accumulation of animal waste is unhealthy. This problem can be dealt with by carefully sealing the entrance holes after the bats have been excluded. Don't leave this step out, it is absolutely essential. If you omit it, the smell of decomposing bat corpses will long remind you of your error.
Conservation and Management of Bats
Bat Population Declines
Bat populations are on the decline throughout the United States. Exact causes of decline are unknown in many cases. In others, loss of habitat by disturbance to roost caves or harvesting of roost trees is certainly a major factor. Insect prey also may have been reduced by enthusiastic use of insecticides.Bats are not abundant in south Florida and their numbers are decreasing in urban areas, so any decline of bat populations is a cause for concern. These declines are largely a result of active and persistent persecution of bats at their roosts by people who are not aware of this creature's gentle nature and beneficial activities.
Until recently, Wagner's Mastiff bat (the only Florida bat found exclusively in south Florida, and also the Caribbean) had not been seen in south Florida for 10 years. Loss of habitat due to changes in architectural design (fewer Spanish tile roofs and fewer chimneys), development of upland forest habitat, and spraying of insecticides are all possible reasons for decreasing observations of this rare species.
Wagner's Mastiff bat sightings should be reported to the Florida Game and Fresh Water Fish Commission by calling (561) 640-6100.
Bat Conservation
Build roosting habitats. You can help bat populations directly by providing them with roosting habitats. To do this you can build a bat house according to the accompanying directions (see Figure 2 ). Bat houses work best (become occupied most quickly) in areas of known bat activity.Use creative landscaping for habitats. Snags, uncut woodlots, and viable wetlands with open water are important bat habitats. Creating your own wildlife habitat through creative landscaping with native plants can also benefit bats. Cabbage palms are a popular landscape tree that is tremendously valuable as a home to bats and other wildlife when left unpruned.
Figure 2. Bat house designed by Bat Conservation Internat'l. How to Build a Bat House
A bat house designed by Bat Conservation International ( Figure 2 ) combines relative ease of construction and temperature buffering features with the varied crevice sizes most often used by American bats. Western red cedar is recommended for its ability to withstand outdoor exposure, though many other woods are suitable. Six feet of 1x12in board and 10ftt of 1x10in board are sufficient for construction. (Sizes mentioned are traditional; actual board sizes normally are about 3/4x9-1/4in.)Overall dimensions may be varied to allow for slight differences in board widths or personal preferences, but spacing between partitions should remain approximately the same. Use rough lumber and turn the rough sides of the roof, front, back and sides inward. The rough side of the ceiling should face down. Cut 1/16-inch horizontal grooves at 1/2in intervals on the smooth sides of all partitions. This will enable bats to climb and roost. Apply a bead of silicon single house costs is less than $20 for materials and caulk along each exterior joint to prevent heat loss. A may become home to 100 or more bats.
Construction Notes:
- Use wood with rough surfaces.
- The space between inner partitions should not exceed 1 inch.
- Hang the completed house 12 to 15ft above the ground on a tree trunk or side of a building facing south or southeast so it catches the morning sun, but is in the shade during mid-day.
Habitat Notes:
Please remember the most important thing any of us can do for bats is to understand them more and fear them less.
- Provide a watering station or locate your bat house near a natural water source to increase your chance of attracting bats.
- Do not use insecticides. Bats eat insects by night, and birds feed on insects by day.
Control Measures for Bats
Although bats are beneficial, they can be a nuisance if they are roosting in your home. The first step in removing bats is to determine where they are entering and exiting the building. Since bats usually leave their roost shortly after sunset, you should watch the outside of your house from 30 minutes before sunset until 30 minutes after.Bats may enter and exit through an unscreened attic vent, a chimney, and cracks or openings along eaves, windowsills, and siding. Once all entrances have been located, seal all but the primary entrance. Next, install a one-way door (bat excluder) over the last entrance. Wait three or four nights, and if you no longer see bats leaving your home then seal the remaining hole.
Although there are repellents on the market, they are generally ineffective and offer only a temporary solution. Poisons are not recommended as they pose a serious health hazard to humans, pets, and wildlife.
Enclose top and sides of entrances to bat colony with nylon netting or wire screening, with an opening 2 feet below entrance (see Figure 3 ).
References
Bats of America. The Univ. Press of Kentucky, Lexington, KY 40506Bat Booklet. Bacardi Imports Inc., Miami, FL 33126
Table 1. Species Accounts of South Florida Bats
Roost Habitat
Status Statewide
Status in South Florida
Identification
Family Vespertilionidae
Twilight bats: The most frequently observed bats in Florida. The tail reaches to the edge of the interfemoral (tail) membrane, but not noticeably beyond.
Eastern Yellow Bat ( Lasiurus intermedius)
Wooded Areas Common
Rare
A large, pale, yellowish-brown bat. Total length from tip of nose to tip of tail = 4.5-5", 11.5-13.0cm. Outer two-thirds of tail is bare. Mostly solitary, but may be seen in groups.
Seminole Bat ( Lasiurus seminolus)
Trees Common
Rare
A medium sized, mahogany brown bat. May have dorsal hairs tipped with white (silver). Found singly or in small groups.
Evening Bat ( Nycticeius humeralis)
Buildings and trees
Common
Common
A smaller bat with dark brown fur, black membranes and a wide blunt tragus. (see Figure 1 )
Family Molossidae
Freetail Bats -- All members of this family have tails extending well beyond the edge of the tail membrane.
Mexican Free-tailed Bat ( Tadarida brasiliensis)
Buildings and other man-made
structures
Common
Common
A medium sized, dark brown or gray bat. Ears are not joined at the base. Total length = 3.5-4.1", 9.0-10.5cm.
Wagner's Mastiff Bat ( Eumops galucinus)
Buildings and trees
Rare
Rare A large cinnamon to yellowish brown bat with the ears joined at the base. Total length = 5.1", 13.0 cm.
Figure 3. Enclose entrance top and sides with nylon netting or wire screening, and drop the material 24" below the entrance.
Footnotes
1. This document is WEC-10, one of a series of the Wildlife Ecology and Conservation Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date December, 1990. Revised September, 2002. Reviewed September, 2202. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.2. Frank J. Mazzotti, Ph.D., associate professor, Wildlife Ecology and Conservation department, University of Florida, Everglades REC, Belle Glade, FL 33430, and Laura A. Brandt, former research assistaant, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.
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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
Copyright Information
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