There are nine species of bats in the Northeast, but these are the only two
that commonly roost in buildings.
Size:
Little brown: 3–4 inches long. 1/16–1/2 ounce. 9" wingspan.
New York's most abundant species of bat.
Big brown: 4–5 inches long. 3/8–5/8 ounce. 12" wingspan.
The Indiana bat, Myotis sodalis, an endangered species found in New
York State, can be confused for the little brown bat. (Remember, an endangered
species cannot be harassed, collected, harmed, or killed without a federal permit,
and your chances of winning the lottery are much better than your chances of
getting a permit to do that.) Of course, an Indiana bat is not likely to be
found in a house. It's not easy to tell them apart, but here's how:
Little brown bat:
Indiana bat:
Brownish nose
Pink nose
Long hairs on toes.
Hairs stick out beyond end of toes
Short, unremarkable toe hairs
Calcar* usually lacks keel, or only has weak keel
Calcar has prominent keel
* The calcar is the bone that juts back from the anklebone to support the tail
membrane. It's "keeled" if there's a flat ridge of skin sticking off
its side that looks like the keel of a boat.
Signs of their presence:
At dawn or dusk, may see bats entering or leaving the building. This is
easiest to see at dawn, because bats swarm and fly around the entrance hole
a few times before entering the roost.
Sounds: Bats can see, but they use ultrasonic pulses to guide their flight
and locate insects (called "echolocation"). Roosting bats may squeak
or scurry when disturbed.
Scat: Piles of black, dry, guano usually found under the main exit hole
in the attic. Can be found scattered throughout an area, particularly in roosts
where bats enter and fly about, but roost in a specific area such as a wall
void or the intersection of the beams and rafters. May also see scat on the
side of the house, usually below a hole or crack. Large piles of guano are
usually found beneath areas that are used often, or by large numbers of bats.
Individual droppings for the little brown bat are about the size of a grain
of rice. The scat of the big brown are about twice that size, and are typically
chunkier, due to the types of insects they eat, such as beetles. Bat droppings
look like mouse droppings, but mouse scat isn't found in large piles, and
is also a little smaller. Also, bat droppings will crumble into powdery dust
but mouse droppings won't. You may see pieces of insect wings, or their reflections,
in bat scat.
Rub marks along the edges of exit holes: Slight brown discoloration that's
a mix of body oils and dirt.
Roosts: During the summer, they'll use different roosts during the day and
night. The daytime roost is usually in an attic, barn, garage, soffit, cave,
underneath shutters or roof shingles, in wall voids, or behind siding or chimneys.
At night, they'll rest in a breezeway, under an awning, or in a garage or
similar areas. In the winter, both species hibernate in colonies in caves,
mines, and deep rock crevices. Big brown bats are more likely to hibernate
in buildings, often in the attic or in wall voids.
Diet:
Entirely insects. A colony of 100 little brown bats can eat hundreds of thousands
of insects each summer. They eat many insects that damage crops and ornamental
plants, such as moths and flies.
Typical activity patterns:
Social style: Females of both species are
colonial, while the males are usually solitary or found in small bachelor groups.
Females roost together to raise their young. Pregnant females look for a hot
niche within the roost that will serve as an incubator. These maternity colonies
are often found in attics, soffits, wall voids, behind chimneys, in barns, tree
cavities, rock crevices, and caves.
Daily activity: Nocturnal, with peak feeding
at dusk and dawn (crepuscular). After feeding in the early morning, they'll
return to the daytime roost and hang out, in a slightly dormant state. After
their evening feeding, they'll usually rest. Females return to the roost often
to nurse their young.
Hibernator?Both bats hibernate in colonies in caves, mines, and deep
rock crevices. Big browns will also hibernate in buildings. The body temperatures
of both species drops to within several degrees of the "room temperature."
Big brown bats can tolerate below-freezing temperatures for short periods, which
is why they are often found roosting in buildings. Their heart rates also drop
dramatically. The little brown's will fall below 20 beats/minute and the big
brown's to 42–62 beats/minute. Compare that to their heart rates during the
rest of the year: 250–450 beats/minute for bats when they're resting, 800+ beats/minute
when they're flying.
Migrates? Both species will migrate locally. Their hiberancula are usually
within several hundred miles of their summer roost, but some big brown bats
will hibernate in their summer roost. (Some of the other species of bats found
in New York, the "forest bats," may migrate far to the south like
birds.)
Where found:
Distribution in NY and the Northeast: Everywhere.
Habitat: Forests and forest edges, areas with lakes and ponds, parks, orchards,
fields, suburbs, cities.
Territory and home range: The maternity colonies begin to disband shortly after
the young are capable of flying, typically in late July. Depending on the weather,
females will remain together through early October. From late July through early
September, bats actively explore new roosts and often show up in locations where
they weren't seen earlier in the year.
Breeding habits:
Pair bonding style: Polygamous. Females raise
young by themselves (although they share the roost with other females and their
young).
Breeding dates: Bats have an unusual habit. They mate during the fall, but
the females store the sperm in their bodies for months. Fertilization doesn't
take place until the late winter or early spring, when the bats emerge from
hibernation or return from the south. Gestation: 50–60 days.
Birthing period: Late May through early July (births are typically staggered
over a 2–3 week period).
Litter size: Little brown: 1 pup; big brown: 2 pups.
Weaning dates: Young begin flying at 3–4 weeks old. In late July, they begin
to leave the roost with their mothers.
Amount of time young remain with parents beyond weaning date: Not well-studied
yet. Some scientists believe that the young probably follow their mothers back
to the hibernacula. Some of the young probably return to the roost in which
they were born.
Common nuisance situations:
Time of year: Peaks from the third week of July through the first week of August,
although there may be calls any time of year.
What are they doing?
Females may roost in colonies in buildings to raise their young. Their scat
and urine can damage insulation and household goods and attract other pests.
Sometimes, a lone bat enters the house and flies around. This usually happens
in July and August, when the young are learning to fly.
During an extreme heat wave, several bats may enter the living quarters,
seeking a cooler roost. This is when they'll show up in places they normally
don't use.
Big brown bats will hibernate in buildings (little browns don't seem to.)
In the winter, a big brown bat may leave its roost in the attic and fly around
in the living spaces. This usually happens when the temperature of the attic
roost changes dramatically, disturbing their hibernation—during a thaw,
or during the very coldest part of the winter, if the attic is much colder
than the rest of the house.
Disease risks: Rabies, histoplasmosis. In New York, bats are a rabies vector
species.
De-bunking myths about bats:
There's an epidemic of rabies in bats. Wrong. The incidence of rabies in
wild bats is very low, and outbreaks in colonies appear to be rare. The Dep't.
of Health has been tracking the percentage of rabid bats in New York since
1965, and the number has remained remarkably constant. They believe it's no
more than 3–4% of the overall statewide bat population—and probably
much less. ("Probably much less," you ask? The Dep't. of Health
knows exactly how many bats
they've examined for rabies and exactly how
many of them were rabid: 3–4%. But theirs is not a random sampling of
bats, as you know. Think about it. In general, bats that are submitted for
rabies testing either exposed a person or pet, or looked sick. Yet, of these
"sick" bats, only a small fraction actually had rabies. So the chances
are good that in the overall population, even fewer carry the virus).
If one bat in a colony is rabid, they're all sick. Wrong
again.
Not all grounded bats are sick! Young pups sometimes become grounded when
they're learning to fly.
Overwhelming fear of contracting rabies from a bat. This is a tricky one.
Although your chances of being exposed to a rabid bat are very low (see above),
it is true that most Americans who died from rabies in the past decade did
have the bat strain. There are probably several explanations. Most people
notice if they've tangled with a skunk, raccoon, or fox. And most people are
smart enough to go right to the doctor if they think they've been exposed
to rabies, so even if they were, they receive treatment and they don't die.
But many people encounter bats at night, while they're drowsy (and not thinking
clearly) or even while they're sleeping. They may not realize they were scratched
or bitten, or may not remember the encounter by the time they wake. So they
see no reason to go to the doctor. Unfortunately, that means that if they
did get infected with the virus, by the time they realize it, it's too late.
The bottom line: this is a fatal disease, so even though
it's unlikely, don't take chances. However, if someone's so terrified
that it's causing problems, try to help that person understand this risk more
clearly.
Bats almost never attack people (they will bite in self-defense).
They are not hair stylists. They don't aim for a person's hair. And bats
are excellent fliers. They may swoop close to a person's face, but if you
don't thrash about, they won't fly into you.
The bats that live in New York eat insects. They don't suck blood. (The
common vampire bat, found in the tropics and sub-tropics, does feed on blood—from
livestock, mostly—but it will bite people.)
Bats don't chew holes in buildings.
Legal status in New York:
Both the little and big brown bat are unprotected. Bats are rabies vector species,
so you may need to consult with the county health department and follow their
guidelines for disposing of the animal.
Best practices
If there's a possibility that a person, pet, or livestock has been exposed
to rabies, you are legally required to follow the directions of the county
health department, no matter what your customer requests. Humanely capture
any bat that had direct contact with a person, was in a room with a sleeping
person, was around an unattended child, or was in a room with a mentally-disabled
or impaired (i.e., intoxicated) person. Call the county health department.
Do not release or discard the bat without talking to a county health person
first!
There's one way in which bats are quite different from many of the other
nuisance species you'll deal with: for most of those animals, removing one
nest site won't affect the local population. But bats have so few young that
the destruction of one maternal colony can probably hurt local bat populations.
Please try to persuade your customers to accept an approach using nonlethal
techniques. They are highly effective for bats.
Safety tips (for contact with bats or their droppings)
Wear leather gloves, disposable Tyvek™ coveralls, goggles, and a
proper respirator.
Ventilate the area, if possible.
Don't stir up dust. The dust could contain the spores of the fungus that
causes histoplasmosis, which can be inhaled. Don't sweep or vacuum, unless
using a commercial vacuum intended for this purpose, and then follow the manufacturer's
instructions.
Instead, thoroughly wet the materials with a household or commercial disinfectant.
Wipe up with a damp sponge. Play it safe and don't use a bleach solution,
because bat guano contains ammonia. Although the concentration of ammonia
in their droppings isn't as strong as it is in bird droppings, there could
be a lot of guano. Do NOT mix bleach with ammonia because the fumes are toxic.
Spray dead bats and their droppings with disinfectant, then double-bag for
disposal.
Be aware of potential pesticide residues in the attic from previous control
attempts.
For more information, refer to chapter four and the resource list.
If one bat has accidentally flown into the house:
Remove any pets from the room, then seal the room. Shut the doors and place
a towel under the door. Close any heat registers. Close all but one window
(which should be screened). Then turn on a dim light. You want just enough
light to see—if you make the room too bright, you'll disturb the bat,
and it will probably try to hide in the most remote, darkest place it can
find. (In a large, cluttered room, searching for a tiny bat is not fun.)
Stay quietly nearby and wait. The bat should calm down in 10–15 minutes.
The air flow from the window should attract the bat, so it should land on
the screen. When it lands, you can capture it by covering it with a plastic
container and slipping a piece of cardboard underneath. If there's definitely
no concern about possible rabies exposure (see above) the bat can be taken
outside and released. (Or you could remove the screen from the window and
let the bat fly out on its own.) If the bat doesn't calm down quickly enough,
leave the room sealed. Return the next day, at dusk. The bat should be calm.
Repeat the dim light-window capture process.
Don't worry about it flying at you, and don't chase or swat at it because
that will only panic the bat. When indoors, bats normally fly around the room
a few times until they find the exit. They make steep, banking turns, flying
up as they approach a wall, and swooping down as they near the center of the
room.
Check the windows, especially if there's an air conditioner in the window.
Gaps between the upper and lower window, or around a storm window, should
be sealed.
Timing of bat-proofing is critical
April through early May (may be in the roost, but no young
yet): complete bat-proofing—with use of checkvalve—is OK
Mid-May through early August (when there are young in the roost): ONLY limited bat-proofing
Late August through November (after the young have left
the roost, and before the weather causes dangerous roof condition): complete
bat-proofing—with use of checkvalve—is OK again
Limited bat-proofing (mid-May through early Aug.):
This approach allows you to protect both the people and the bats. Seal potential
points of entry into the living quarters (most important step); then work on
unused cracks and holes on the outside of the building. There are probably many
of them, because bats can enter a building through a crack that's only 1/4"
wide by 1 1/2" long, about the size of a stick of gum or a stubby pencil.
Do NOT seal the primary hole, and don't separate the mothers from their pups.
You must let the females enter and exit the building freely.
Complete bat-proofing (April through early May,
then again from late-August through November):
First step: Find their entrances. Inspect the house for signs of warped, shrunken,
or loose materials, especially at joints. Pay special attention to roof drip
edges, dormer tie-ins, roof corners, ridge caps, vents, and deteriorated walls,
roofs, and eaves. In the attic, cover the windows, then turn off the lights.
Look for light peeping through gaps, cracks, and holes. Then use a flashlight
to take a better look at these potential entry points.
Second step: Determine which entrance is the primary exit hole. Here are few
ways to do that. Look around for piles of guano, which may accumulate beneath
the primary exit hole, or stick to the wall near the hole. Rub marks are typically
seen on the wall if there's guano stuck to the wall. Or stage a "bat watch."
At dawn or dusk, stand outside the building and watch where the bats enter or
leave. Why bother? Because if you seal this hole while there are still bats
inside, they'll probably panic and fly into the living spaces as they frantically
seek a way out of the building. There's an easy way to avoid this problem: install
a "checkvalve" (one-way door) over the main exit hole (see below).
Using a one-way door (checkvalve) to exclude bats:
This will allow the bats to leave on their own, but they won't be able
to get back inside. Here's how it works. Bats exit at bottom, but when they
attempt to return, their sense of smell guides them back to the hole. They
land on the mesh near the hole—and stay there, sniffing around. They
just don't crawl down the mesh. (Good thing: if they did, they would be able
to slip back underneath the mesh, crawl up the building, and find their hole.
But don't worry about that. They trust their noses.)
You can use a commercial checkvalve or make your own, following this design
developed by Dr. Stephen Frantz, NYS Dep't. of Health: Place 1/4" or
1/2" polypropylene mesh or screening over the entrance holes, forming
a long sleeve or tent. The screening should cover the hole and extend about
3 feet below the hole. It also should stick out about 3–5 inches from
the wall, so the bats can crawl beneath the screen to leave. Secure the screening
at the top and sides with duct tape or staples; leave the bottom open. Leave
the screening in place for 3–5 days and check that all the bats have
left. Then you can remove the one-way door and permanently seal the hole.
If there are no young present, or this is a preventive action, you can:
Install a one-way door to allow any bats that are still inside to leave
the building.
Seal all cracks that are larger than 1/4" wide by 1 1/2" long
and holes that are larger than 1/2" × 1/2". Bats can wriggle
through very small holes! Bats can't chew through exclusion materials the
way rodents do, so you have many choices for materials: caulk; expanding foam;
"Stuf-Fit,™" a knitted copper mesh that's like steel wool,
only it doesn't rust; window screening; bird netting; or "flash-band,"
a self-adhesive aluminum-faced sealant. Some NWCOs seal cracks with expanding
foam using the Todol™ foam gun, and then finish with a bead of silicone
over that. The mesh size of screening or netting shouldn't be larger than
1/2" × 1/2" or the bats will be able to crawl through it.
Screen chimney flues and caps with mesh that's 1/2" or smaller. (Remember
to check local fire codes for information about covering chimneys.)
Seal any gaps in the flashing around the chimney, and where the chimney
cap meets the chimney.
Screen vent pipes with 1/4" mesh.
If the bats are roosting behind shutters, remove the shutter or space it
further away from the wall by installing small blocks between the shutter
and wall.
There are two ways to change an attic that may make it less attractive to
the bats. Neither has been well-studied. It's also possible that the bats
will simply move into another area without leaving the building. But here
they are: 1) Increase the ventilation and decrease the temperature of the
roost area, so it's not as attractive an incubator. In attics, install fans,
windows, ridge or soffit vents, or insulation in the walls. 2) If you can't
seal all of the holes, install a few floodlights or fluorescent bulbs in the
roosting area. The lights should be left on all day and all night for several
weeks. In later years, turn the lights on during the spring or summer occasionally,
to discourage the bats from recolonizing the site. Leaving the lights on for
so long could increase the risk of an electrical fire.
If young are present:
Wait until they're old enough to fly—usually by mid-August. Then,
install a one-way door over the entry hole. They'll leave but won't be able
to re-enter.
Trapping strategies:
Live traps:
A resting bat can be captured with a plastic container or a butterfly net
(wear leather gloves). If you can reach it, cover the bat with the container,
then slip a piece of stiff cardboard between the container and the wall. To
release the bat, hold the container on its side on a secure place, such as
against a tree, or on a ledge. Then remove the cardboard.
One-way doors. See previous description of use in the section on complete
bat-proofing.
Multiple-capture traps. There are several different types and sizes of
multiple-capture traps for bats. The Batrap™ consists of a tube that
leads the bats through a one-way baffle into a chamber, in which they're confined.
Like a one-way door, this trap allows the bats to leave the building but keeps
them from re-entering at that spot. (Of course, you'd still need to bat-proof
to make sure the bats can't enter the building in other places.)
Multiple-capture traps are a bit trickier to use than a one-way door. If you're
inexperienced with this tool, try to learn its proper use from a skilled NWCO.
For example, it's important to correctly estimate the number of bats in the
roost. You need to match the size of the trap to the number of bats that may
be captured, because if too many bats are confined in the trap, they might
suffocate. Another danger is that if bats remain in the trap too long, they
might overheat from exposure to the sun, and die.
If your customers insist on seeing the bats, a multiple-capture trap will
satisfy that need and allow you to then release or relocate the bats. (If
the customer insists on having the bats killed, this is a safe way to capture
them. But do try to talk them out of that.) One benefit of using a multiple-capture
trap is that it may create a great "teachable moment." You can show
the bats to the neighbors and talk to them about the benefits of having bats
around, and de-bunk myths. You may be able to convince them to bat-proof.
Another option that allows you to prove that you got rid of the bats is to
use a one-way door and a video camera. Place the camera near the exit holes,
set it to record, and leave it running. Then you can show the tape of the
bats leaving the roost to your customers.
What to do with the bats:
Follow the Dep't. of Health's directions if there's been rabies exposure,
or if dealing with a sick bat, one's that grounded, or one that's behaving
strangely.
For healthy bats that can be released, on-site release (coupled with bat-proofing,
of course) is preferred over relocation.
Relocation is tricky. Bats will fly great distances to return to a favored
roost, so if the customer didn't bat-proof, the problem may happen again.
You'd have to travel hundreds of miles to make sure the bats wouldn't be likely
to return to that spot. If you did that, what would happen to the bats during
the trip? If some became too stressed or overheated, they might be grounded
after release. That might increase the disease exposure risk for people, pets,
and wildlife in that area. Also, how fair is this to your customer's neighbors?
Sure, they see you capture the bats and take them away, but you know the chances
are good they'll return.
Special concerns with very large maternity colonies: If the site is really
good, there could be thousands of bats, perhaps as many as 3–7,000.
Obviously, the bats have been there for a long time. Can you convince your
customer to choose the two-season solution instead of the quick-fix, which
might cause long-term harm to the local bat populations? Here's what a more
relaxed approach would look like. In the first year, you install two or three
bat boxes in the early summer. Let the bats raise their young in the building,
and give them time to check out those newly-installed boxes. In the late fall,
you can begin limited bat-proofing, but don't close the main entry hole. In
early May of the following year, install a checkvalve over the main hole.
Once you are certain all bats are out of the structure, you can finish permanent
bat-proofing by sealing the primary entrance hole.
Offer the bats an alternative roost nearby by installing a bat box in the
yard (optional, but highly recommended, especially for larger colonies). Why?
Many people find that they like having bats nearby, because of all the insects
they eat. Another good reason to install a bat box is that it may prevent
that colony from moving into a nearby building. Installing bat boxes this
far north does require some careful planning. See A
homeowner's guide to northeastern bats and bat problems from Penn State
University or contact a bat specialist or Bat
Conservation International for details. It's best to locate the bat box
where people are less likely to encounter the bats. If this isn't possible,
the area immediately around the box can be fenced to prevent people from disturbing
the colony and encountering a bat that's fallen out of the box.
Preferred killing methods:
CO2 chamber (a smaller chamber is better)
Acceptable killing methods:
If there's been no rabies exposure, with care, can use stunning and chest
compression. Be careful about contact.
Methods that don't work well, or aren't legal in New York:
Ultrasonic devices aren't effective.
Customers may also ask about using moth balls or insect spray. Moth balls
can be dangerous, especially to children. One of the active ingredients, napthalene,
can be inhaled, eaten, or absorbed through the skin. That means that if you
store clothing with moth balls, you can absorb the chemical the next time
you wear the clothes. It's true that napthalene is registered as a pesticide
for bats in New York, which means that NWCOs with a commercial pesticide applicator
license can use the product. Napthalene flakes may help to repel a bat colony
if the site is confined and has little or no ventilation, but the recommended
application rate is high, and vapors could enter the living spaces and endanger
people.
