Big Brown Bat by Chris Burney

Bats: Chiroptera

Appearance:

Bats belong to the mammal order Chiroptera, which means "hand-wing." They are the only mammals that can truly fly. Florida has 13 resident bat species External Website. Contrary to popular belief, bats are not blind, and many species see quite well. Because they are active at night, bats are adapted for seeing in dim light. Even in complete darkness, bats are agile, highly maneuverable fliers because they use echolocation to guide themselves. Echolocation is the use of sound waves to detect objects. Bats emit high-pitched sounds and listen for them to echo back. The length of time it takes the echo to return tells a bat how far away it is from an object. This helps bats to be very skillful flyers in the dark and to hunt successfully for food. Bats are more comfortable in darkness and often are reluctant to fly in the daytime, even when disturbed.

The wings of bats are supported by the bones of the arms, as well as bones of the hands and fingers.  Some bats have long, narrow wings, while others have shorter, but broader, wings. Wing membranes are very thin, but are living tissue.  Wing membranes usually extend down along the bats’ sides and are connected to their hind legs and at least part of the tail. Bats' feet are small and not very good for crawling, but they are uniquely adapted for grasping structures in a way that allows the bats to hang upside down.

Most small mammals have short life spans.  But bats, for their size, have the longest life spans of any mammal. Some bats can live for more than 30 years.

Habitat:

Bats live in many different habitats across Florida. They can be found in dry, upland pine forests, in the hardwood forests along the banks of rivers, and most habitats in-between. You can probably even find them flying around in your neighborhood! For bats, one of the most important parts of their habitat is a place to roost. Some bats, like the Brazilian free-tailed bat, the evening bat, and the big brown bat are colonial, meaning they gather together in a colony to roost during the day. Other species, like the Seminole bat and the tricolored bat, are solitary, meaning that they roost by themselves. In Florida, natural roosting sites can be caves, in cracks, crevices, or hollows of trees, under dead fronds of palm trees, and in Spanish moss. Bats also use manmade structures including buildings, bridges, culverts, tile roofs, and bat houses.

Behavior:

Florida's native bats are insectivorous, meaning they eat insects including beetles, mosquitoes, moths, and other agriculture and garden pests. In fact, bats do a great job of helping to control insects because a single bat can eat hundreds of insects in a night!

In Florida, bats mostly mate in the fall and winter. But female bats usually do not give birth until the spring when insect populations increase. Most female bats give birth to only one baby bat, called a pup, each year. For their size, bats are the slowest reproducing mammals. Bats do not build nests. Pregnant females of some species will gather together in nursery colonies when they are ready to have their pups. They normally give birth from mid-April through July, and their young begin to fly within 3 to 6 weeks. The young bats are usually weaned from their mothers by mid-August, when the juveniles are able to fly and search for food on their own. Bats will not reach reproductive maturity until they are about 1 year old. This is considerably longer than most small mammals.

 

Bats and People

Bats, like many other wildlife species, have lost a great deal of natural habitat to development. And bat populations are declining in size in many areas. One reason for that is the loss of roosting sites such as trees and caves. Some bat species have been able to adapt to the loss of natural roosting sites by roosting in buildings and other man-made structures where they are more likely to become a nuisance for people. Bats of some species will roost together in large colonies, especially females when they form nursery colonies. The possibility of causing disturbance or harm to large numbers of bats that are roosting in buildings means those bat populations can be particularly vulnerable to people’s actions. The use of pesticides to control insects may have unseen impacts on bat populations, by taking away the food they eat, or sometimes poisoning the bats themselves if not applied well.

These unique mammals are of little threat to people.  But, because bats often have been sensationalized in the news and horror movies, they create a great deal of anxiety among many people. Fear of rabid bats has caused mass destruction of bat populations for decades even though bats seldom pose public health problems. Rabies, a virus usually transmitted from a bite, affects a very small portion of bats – perhaps only one among every few hundred bats across all of the bat populations in Florida. Histoplasmosis, a respiratory illness caused by a fungus, is rare, but is another health concern that people sometimes associate with bats. This fungus is found in soil that is enriched with bat or bird feces. This fungus is sometimes found on chicken farms or in caves. According to the Florida Bat Conservancy, "this illness has been associated with bats in Florida in only a few cases, all of which involved visits to bat caves." Attics and other spaces in buildings are normally dry areas that do not provide the proper conditions for this fungus to survive.

People should not handle sick, injured, or dead bats.  For more information about bats and rabies or histoplasmosis, including what to do if a person makes contact with a bat, contact your county health department, the Florida Department of Health, or the Centers for Disease Control and Prevention (CDC).

Report sick, unusually behaving or dead bats

 

White Nose Syndrome

White Nose Syndrome (WNS) is named for a white fungus that has been found covering the muzzles and wings of hibernating bats in the eastern part of the United States.  More than a million bats with WNS have died, but fortunately no cases of WNS have been found in Florida. WNS is spreading and biologists now know that both bats and people can carry the spores of the fungus between sites. There is no indication that people have been affected by WNS from exposure to the fungus or affected bats.

Learn more about White Nose Syndrome

 

Legal Protection for Bats

It is illegal to kill bats in Florida in accordance with Florida Administrative Code rule 68A-4.001 General Prohibitions.  Since bats are particularly vulnerable to disturbance and harm when they are roosting in buildings and other man-made structures, protections for bats in structures are also included in rule 68A-9.010 Taking Nuisance Wildlife. This rule does not allow the use of pesticides or poisons for the purpose of harming, killing, or deterring bats.  There is one legal, registered repellent that can be used for bats: naphthalene (also known as moth balls). Unfortunately, moth balls are rarely effective or practical in repelling bats from a structure.  This nuisance wildlife rule also states the minimum requirements that need to be followed if someone is going to remove bats from buildings and other structures.

 

When Bats are Living in Buildings and Other Structures 

When bats take up residence in a structure where they are not wanted, the legal, safest, and most effective technique for getting rid of them is a process known as "exclusion." Excluding bats from their roost sites involves the use of a one-way exclusion device that allows them to exit the structure, but prevents them from returning. After the bats are gone, the device is removed and the entrance holes into the building are sealed.  Prior to excluding the bats, any other potential openings the bats might use should be sealed, which includes openings as narrow as ½ inch. Bat-proofing for most structures often requires nothing more than simple improvements that make buildings more energy-efficient, such as applying caulking and weather stripping.

When bats are present in a building, it is a legal requirement in Florida that one-way exclusion devices must be used for four consecutive nights, to ensure that all bats have left before the openings are sealed.  There is a further legal requirement that bat exclusions cannot be conducted if the National Weather Service forecasts four consecutive nights in which the minimum temperature is below 50 degrees Fahrenheit. This is to keep inactive bats from being trapped inside a structure.

Another legal requirement in Florida is that bat exclusions cannot be conducted between April 15 and August 15 because that is when young bats are born, and the babies are not able to fly or feed themselves for several weeks.  During that time, if the mothers fly out of a building and can't return, they are separated from their flightless young, leaving the young bats trapped in buildings where they will die.  No permit is required to exclude bats from a structure between August 15 and April 15.

The minimum legal requirements apply to bats statewide, but additional precautions are often recommended to help prevent the possibility of having dead bats in buildings.  The additional precautions are based on experience showing that because of weather conditions and differences between the north and south part of the state in temperature, species of bats, and bat behavior, the minimum requirements sometimes don’t protect all bats.

We recommend that exclusion devices be left in place at least 5-7 days whenever possible. That is especially important when outside temperatures drop below 60 degrees Fahrenheit, or there is rain. During cold weather, bats often become inactive and may not exit the structure.  Rainy weather also can cause bats to be inactive and not emerge.  These recommendations will help make sure that all the bats have left before the building is sealed, so that bats don’t die in the building, or enter interior rooms, which could cause health concerns for people inside the building.

 

Summary Table of Legal and Recommended Exclusion Practices

 

 

Legal Requirement

Recommended Safest Practice

Season

Only between August 15 and April 15

Only between August 15 and April 15.

But, in South Florida, additional caution should be taken because the Florida bonneted bat, is found there. This is a Threatened species and the maternity season for this bat is not well understood. So additional caution should be taken in that area, even in winter months. If young bats are found, they should be reported to FWC. 

Temperature

Temperatures above 50°F

Temperatures above 60°F

Duration

4 nights (all above 50°F)

5 to 7 nights, especially if there is rainy weather or the outside temperature drops below 60°F.  Exclusion devices should stay up until building repairs are started. 

Method

One-way physical barrier known as an exclusion device

Exclusion devices are safest when monitored regularly and carefully installed following the Exclusion Process guidance below. 

 

Exclusion Process 

If a bat exclusion is going to be done on a building, it is important to make sure the exclusion is done properly to avoid having bats die inside the building or die as a result of becoming trapped in the exclusion materials.  A good first step for an exclusion is to make sure that the bats cannot get from their roost area to rooms inside of the building after the exterior openings are closed off.  Then, before doing anything else, watch at dusk to identify the exit areas where the bats leave the building. The next step is to close up all cracks, crevices, or similar openings on the exterior of the building, except the exit areas the bats are using.  Use caulking, flashing, or heavy-duty plastic mesh to bat-proof all the openings, away from the exit areas. 

At the bats’ exit areas, carefully install one-way exclusion devices over each of those remaining openings.  Exclusion devices must be installed correctly to be effective at allowing bats to leave, but not re-enter.  Once installed, exclusion devices should be checked 1-2 times per day to make sure bats have not become stuck and are able to exit safely. 

One-way exclusion devices can be either curtain-style, constructed from heavy-duty plastic mesh, or tube-style, constructed from flexible plastic tubing.  Exclusion tubes should be about 2 inches in diameter and about 10 inches long.  The one-way exclusion tubes can be made from flexible PVC pipe or flexible plastic tubing.  Empty caulking tubes also can work well but only after the caps and tip have been cut away and the tubes have been thoroughly cleaned. The important detail is that bats must be unable to cling to the smooth inside surface of these tubes.  

If flexible plastic mesh is used to construct a curtain-style exclusion device, the mesh should have openings about 3/16 inch to 1/4 inch in size. Heavier gauge, or heavy duty plastic mesh is usually preferred. The plastic mesh can be used to form a one-way exclusion device over narrow openings in exterior walls, or attic louvers. Securely attach the top of the plastic mesh material above the opening. Then securely attach the sides of the mesh and have it extend 18 to 24 inches below the bottom of the opening.  It is important to leave the bottom of the mesh unattached, but hanging loosely against the wall so that bats are able to crawl down and out, but not able to crawl back up under the mesh. It’s extremely important to have the sides and top of the mesh securely attached with water-based caulk, or something similar.  Small nails or staples can be used in some situations to attach the exclusion device, as long as they can’t injure the bats.  Duct tape usually is not a good choice because it frequently becomes unattached from the wall. If using caulk, be sure to allow enough time for the caulk to dry before dusk when bats emerge.

During the exclusion process, some bats may return to their exit areas at dawn, find them blocked, and hang onto netting material or the structure, even in an exposed area.  This is not unusual and is not something to be alarmed about. 

Exclusion devices can stay up longer than 7 days, if necessary because repairs can’t be completed before dusk or can’t be scheduled immediately.  It is very important to complete the work needed to repair openings in the structure immediately – the same day – that the exclusion materials are removed so that bats are prevented from re-entering the structure. 

More details on how to conduct a bat exclusion and the equipment needed to do that are available from Bat Conservation International External Website and the Florida Bat Conservancy External Website.  Exclusion devices can sometimes be constructed and installed by someone who has basic handyman skills.  However, if you want contact information for experienced companies who can conduct a bat exclusion for you, contact your closest FWC Regional Office.

 

How You Can Help Protect Bats

  • Avoid disturbing maternity colonies or entering caves where bats are roosting.
  • Never shoot, poison, or otherwise harm bats.
  • Be cautious when using insecticides.
  • Use caution when trimming trees and Spanish moss to avoid disturbing roosting bats.
  • Do not try to handle bats.
    • In general, you shouldn’t try to handle bats without experience or the assistance of a professional.
    • Bats are very delicate creatures and are easily injured if handled.
    • Handling bats increases the chance that you might be bitten.
    • Seek medical help if bitten by a bat.
  • Construct a Bat House
    • Bats are so effective at controlling insects that some people attempt to attract bats with bat houses. You can find information on constructing or purchasing a bat house at Bat Conservation International External Website and Florida Bat Conservancy External Website.
    • Bats are a very important natural resource for Florida because each bat can eat hundreds of insects per night, including mosquitoes and agriculture pests.
    • Bat guano (feces) has been used for centuries as a nutrient rich fertilizer and is still highly prized by gardeners.
  • Support Bat Conservation!
    • There are many bat organizations that need more volunteers and support. Links to some bat conservation organizations are listed below.

 

Additional Information:

If a Bat has Gotten Inside Your House

Bats that are Found in Florida

Bat Conservation Organizations

Health of Bats


Image Credit: Chris Burney



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