[Annual Wildlife Control Issue] A Bat Habit

Features - Annual Wildlife Control Issue

Bat experts discuss the biology, behavior and potential new regs protecting this beneficial mammal.

September 24, 2013
Anne Nagro

Editor’s note: This article originally appeared in the Pest Control Canada e-newsletter, sponsored by Univar Environmental Sciences. To receive this e-newsletter, email jdorsch@giemedia.com with the subject line “subscribe Canada.”

The United States has 47 species of bats. Three commonly roost in structures. Three experts — Dr. Brock Fenton, University of Western Ontario, Bat Conservation International Outreach Associate Dianne Odegard and Ann Froschauer, U.S. Fish and Wildlife Service — offered a look at this fascinating animal:

Common Tenants.
Bats roosting in attics or eaves often are the little brown myotis, big brown bat and Mexican free-tailed bat, said Odegard. Most bats weigh between 4 and 20 grams.

Long Lifespan. Bats usually bear one pup a year, though big brown bats have twins. Mating occurs in August–September. Females store sperm through the winter and get pregnant in April. Young are independent by August. A bat found roosting on the outside of a building around this time is likely a lost young. Adult bats live a long time: The oldest little brown myotis on record is 34 years in the wild. In Europe, it is 45 years.

Hibernation Hideaways. When weather turns cold, some bat species migrate south or to different habitats within their summer range, said Odegard. The little brown myotis stays local and hibernates in abandoned mines and caves. The big brown bat may overwinter in the walls of structures where the temperature stays just above freezing. Mexican free-tailed bats enter a state of torpor when insects become unavailable in cold weather. While hibernating bats go the entire winter without food, bats in torpor need food and drink after 10 to 14 days, Odegard explained.

Hot Property. In the spring, females leave hibernation sites to find hot places, such as attics or eaves, to raise their pups, said Fenton. Hot babies grow faster that cold babies, and hot females produce more milk than cold females. Bats congregate in these spots. The biggest colony Fenton saw was 3,000 little brown bats in an old farmhouse north of Kingston, Ontario. Don’t perform exclusion while females have dependent young. Having females outside while dependent young inside starve to death “is not a good combination,” said Fenton.

Insect Eaters. All bats eat insects and the odd spider. They have a voracious appetite and high metabolic rate: A typical male eats half his body weight in insects every summer night. A lactating female eats 120 percent of her body weight.

Rabies Warning. Bats are susceptible to rabies, which can be transmitted to humans by bite. Do not handle bats unless you’re specially trained and have had your rabies shots.

New Endangered Species? Nearly 7 million bats in North America have died from white-nose syndrome, a rapidly spreading fungal disease found in 19 states and 4 Canadian provinces.

In response, the federal government is assessing all bats threatened by the disease and is considering listing the northern long-eared bat, eastern small-footed myotis and little brown myotis as endangered species, said Ann Froschauer, national White-Nose Syndrome communications leader for the U.S. Fish and Wildlife Service.

Rulings on the Northern long-eared bat and Eastern small-footed myotis are expected in 2013, she said. A decision on the little brown myotis may take longer given its widespread range across the U.S.

Massachusetts and Vermont already have listed threatened bats as endangered. Pennsylvania is considering the move, and more states may follow.

In Canada, the little brown myotis, northern long eared bat, and tri-colored bat are being considered for federal endangered status. A similar request was made in the province of Ontario.

Bats in the Belfry? It’s likely one of these three species:

1) Little brown myotis
(Myotis lucifugus)
This bat has long, glossy fur colored pale tan to dark brown. It’s found in wooded areas throughout Canada and the northern United States. In summer, females form nursery colonies in buildings, tree hollows, rock crevices and under bridges. In winter, they hibernate in caves and mines.

2) Big brown bat
(Eptesicus fuscus)
Relatively large, this bat has a broad nose and fur colored light rust to dark brown. It lives throughout Canada and the U.S., except for central Texas and extreme southern Florida. Females form nursery colonies in buildings or hollow trees; males live alone or in small bachelor colonies. They hibernate singly or in groups up to 100 in caves, buildings and abandoned mines.

3) Mexican free-tailed bat
(Tadarida brasiliensis)
This medium size bat has dark brown to gray fur. The largest U.S. populations live in the West, with the densest concentrations found in Texas. Maternity colonies in limestone caves, abandoned mines, under bridges, and in buildings can number in the hundreds of thousands to millions. Researchers estimate 100 million Mexican free-tailed bats in Central Texas eat 1,000 tons of agricultural pests each night.

More info: Bat Conservation International - www.batcon.org

Photo credits: Little brown myotis (Rinus Baak | Dreamstime.com ), Big brown bat (Ann Froschauer/USFWS) and Mexican free-tailed bat. (USFWS/Ann Froschauer)


If a species like little brown myotis is deemed at risk, bat exclusion will become “more complicated,” said Fenton. A special permit may be required to work with these species, said Froschauer.

Endangered species cannot be denied critical habitat, which includes where females have their young, reminded Fenton. Still, exclusion likely can be done in a way that won’t “put you outside the law,” like performing it from November to March when the little brown myotis is hibernating underground, he explained. Or, home or business owners could apply for an exemption.

“We would never put somebody’s health and wellbeing at risk if they had bats in their home,” said Froschauer.

Stay tuned.


Anne Nagro is a PCT contributing writer. Dr. BrockFenton of the University of Western Ontario is one of Canada’s leading experts on the behavior and ecology of bats. Founded in 1982, Bat Conservation International is devoted to conservation, education and research initiatives involving bats and the ecosystems they serve.


Bat Exclusion: Expertise Required

Bat exclusion is a big ticket, complex service. Here are tips for success. 

By Anne Nagro

Bats are beneficial, threatened and legally protected. They’re small – weighing a mere .16 to .70 ounces – and easily find their way into structures through 1/2- to 1/4-inch gaps. They’re also loyal. Randy Hobbs, VP of Bedford, Nova Scotia-based Braemer Services, recalled a client’s century-old house where bats had been returning to roost for 60 years. “They had thousands of bats. They had droppings in the attic between four-and-a-half and five feet deep.”

The only way to prevent bats from roosting in structures is exclusion, which is not a simple process. To help you succeed, experts shared these tips:

Assess the colony.
Watch bats leave the structure in the evening to determine how many there are and key entry/exit points. If possible, identify the species.

Install artificial roosts. Before exclusion work begins, put up bat houses to give bats a new place to roost, said Dianne Odegard, outreach associate at Bat Conservation International. This will give displaced bats shelter, protect them from predators and possibly prevent them from settling in neighbors’ attics. Exclusion at a Texas sports stadium caused thousands of Mexican free-tailed bats to seek shelter at nearby homes. Bat houses must be properly constructed and sited.

Exclude at the right time. Hobbs waits until bats have migrated in fall or before they return in spring to perform exclusion work. Don’t exclude them while females have dependent young or the pups may starve to death inside, explained Dr. Brock Fenton of the University of Western Ontario. Young are independent by late August, but the roosting site should be empty by late fall. Bats hibernating in a structure should not be excluded until spring when food and temperatures are favorable. Don’t go into the colony, catch or handle bats unless you’re specially trained and have had rabies shots.

Find all holes. Bats don’t have the teeth or claws to make their own holes; they use existing openings to get inside. Finding these access points is a challenge on older structures, where warping wood and wear and tear can cause many gaps. Look for holes where cable and pipe enter a building and where the roof joins the walls. Other areas include: chimney, soffits, loose shingles/tiles, loose flashing and areas where siding forms corners or meets doors or windows. In stadiums and parking garages, bats may roost in expansion joints between concrete beams. Look for black or brown stains caused by bats’ body oils or droppings around cracks and crevices.

Seal gaps. While bats roost during the day, seal the entire structure using screen and caulk except for those holes where bats freely come and go. If bats are getting into the living space, work with the homeowner to identify and seal interior gaps and install attic and basement door guards.

Install one-way valves. Where bats come and go freely, install one-way valves to ensure they get out but not back in. Common devices are made from tubes, plastic sheeting and polypropylene netting. See Bat Conservation International’s instructions on building and installing these devices (see www.batcon.org/pdfs/education/fof_ug.pdf). Traps and relocation are not approved exclusion techniques, except when capturing a single bat for species identification or removing a bat from an indoor living or work space.

Monitor and remove. Visit the structure on a night without rain to determine if bats are freely leaving the one-way doors and that you haven’t missed any entry points, said Hobbs. He learned this the hard way: At the century-old house job, returning bats tried to gain entry through the chimney, which didn’t lead to the attic but to the living room. “We spent a few days chasing thousands of bats out from inside the home.” Leave the valves in place for 5 to 7 days. Once you’re comfortable all bats have gotten out, remove these devices and seal the holes.


7 Million Bats (and counting) Succumb to White-Nose Syndrome

Nearly 7 million bats have died from White- Nose Syndrome in North America, according to the U.S. Fish and Wildlife Service. First documented in New York in 2006, the fast-spreading disease has been found in 19 states and 4 provinces.

Caused by the fungus Geomyces destructans, the disease attacks hibernating bats. Most noticeable is the white mold-like growth on bats’ faces and wings, but infected bats also exhibit unusual behavior, like flying outside during the day and clustering near the entrances of caves and mines when they should be hibernating. Mortality rates are approaching 100 percent at some caves.

The little brown myotis, once the most common bat in the northeastern United States, has taken “a terrible hit” with more lost than any other species, said Bat Conservation International Outreach Associate Dianne Odegard. “It’s frightening to think that a plentiful, common species can actually be at the point of regional extinction in a period of five or six years.”

Scientists expect the disease to continue to spread, said Ann Froschauer, national White-Nose Syndrome communications leader for the U.S. Fish and Wildlife Service. The fungus likely was transported accidently by humans on gear or shoes from a cave in Europe.

More info: http://whitenosesyndrome.org


Clean up. In addition to exclusion, Braemar Services cleans up droppings, removes contaminated insulation and installs new insulation. Proper safety gear, including a respirator, is necessary.

Set expectations. Missing a key entry point is a very real possibility. When the bats find their way back in, customers can get grumpy. Take time to set expectations for service, follow up and the time frame for completing the job.

Note: Before undertaking bat exclusion, make sure you have the proper training and licenses.


Visit “online extras” on the PCT Online home-page for a listing of bat-related websites and a list of bat experts and resources.