Introduction
Bats can become a nuisance when they invade dwelling structures. Their presence,
ectoparasites, and odours from fecal matter and urine, and are all of concern.
Nevertheless, bats represent important members of the wildlife community
and should be valued for the role they play as predators of insects. A single
brown bat can easily capture 600 mosquitoes in an hour while a colony of 500
bats can eat a million insects nightly.
Bat Biology
Bats, the only mammals capable of sustained flight, belong to the order Chiroptera,
which means "hand-wing". Out of the 900 bat species known in the world, about
40 species, mostly insectivorous, are found in Canada and the United States.
While some species can be larger, bats are usually not much bigger than a house
mouse. The wingspan of the two most common Canadian species, the little brown
bat and the big brown bat, ranges from 8 to 14 inches. Bats will mate in fall
or winter and the pups are usually weaned in July or August. A few bat species
will migrate to the south when cold weather approaches while other species
will just move to caves or mines where the temperature does not go below
the freezing point.
In some cases, the big brown bat will even roost in buildings throughout the
winter if conditions are favourable, e.g. high humidity level and temperature
above the freezing point. Bats are loyal to their birthplaces, often returning
to the same roost site year after year. A bat can live more than 10 years.
Bats emit high-frequency sounds inaudible to humans. These sounds bounce off
objects in their paths to enable them to avoid obstacles and detect flying
insects. Sometimes bats can be seen around outdoor lights, which attract insects.
Contrary to popular belief, bats are not blind. In fact, some species have
excellent vision.
To save energy, bats have the ability to enter a dormant state which make
them appear to be sick, asleep or dead. They may also bare their teeth and
squeak loudly, leading many people to believe they are vicious. In reality,
the helpless creature is only trying to ward off a possible attack.
Bats must also avoid the watchful eyes of their many predators, which include
hawks, falcons, owls, cats, snakes, and humans.
Bats in the Attic
Signs of infestation
Bats are usually detected by their droppings or noise-making. The musty smelling
droppings can easily be mistaken for those of mice or birds. However, bat droppings
can be crushed into fine, shiny undigested insect parts. By contrast, mouse
droppings are firm and do not disintegrate readily. No white colour appears
in bat feces as in bird feces.
Roost site identification
In order to determine whether bats are roosting in a structure, its exterior
should be inspected before bats leave their roosts (before dark) or when they
return from their night escapade (at dawn). Refer to picture 1 for possible
entry sites. A watch of an hour or so for a few days should be sufficient to
identify all possible entry and exit ways.
Because bats are nocturnal creatures, they will not leave their roosting sites
if they are faced with bright light.
Therefore, while inspecting the outside of a structure, one should maintain
a dim light by fixing several layers of red cellophane over the head of a flashlight
with a rubber band.
Taking count
Marking the entry sites down on a plan of the house and counting the number
of bats exiting or entering the building will be a great help when monitoring
the results of your control program.
Bat Control
When a bat infestation takes place in your house, you might consider excluding them either by "bat proofing" the structure yourself, installing bird netting, using lights to disturb them, providing alternative bat houses or hiring a company to exclude bats from a structure. A combination of these methods would be most effective. One may be interested to know that newly installed bat colonies will be easier to dislodge.
The best time to control bats is in the spring, before migratory bats return
to the roost, or in the fall, when migratory bats have left for the season.
This is important in order not to kill the young bats that may be trapped inside
the structure. Their carcasses would eventually create an odour and insect
problem.
Bird Netting
The installation of bird netting (polypropylene netting) stapled or duct-taped
over entry points, the bottom part hanging loosely one to several inches from
the building, will enable the bats to crawl under and exit the roost site.
On the other hand, returning bats will not be able to re-enter. Refer to the
picture above for an example.
The building should be watched for several evenings at dusk to ensure bats
have not found another entry in the same structure. After three to five days,
when no more bats are seen exiting the building, the netting can be removed
and the holes sealed as stated in the following section.
Bat Proofing
Bat proofing a structure is the best way to manage a bat infestation on a
permanent basis. It is essential to seal all points of entry such as spaces
under eaves, electrical conduits, and holes around the chimney and windows.
Picture 1 provides possible entry points. Vents that must be kept open can
be protected with a fine screen. Larger openings can be sealed with a high
quality caulk, lath, sheet of metal, or window screen. Unlike rodents, bats
will not gnaw their way through, but they will push away loose barriers./p>
Use of Lights
Since bats tend to avoid daylight, illuminating an infested attic may cause
them to leave for another location. This method is believed to be most effective
if done shortly after bats return from their hibernating sites. It may, however,
not be as effective if it is impossible to direct the light to all roosting
sites.
Bat Houses
Bats are important insect predators and therefore should be encouraged to roost
in our neighbourhoods in structures other than those where people are living
and working. One way to achieve this is to install bat houses in trees, where
bats will not represent a nuisance. Bat houses can be purchased in hardware
stores and garden centers or easily built with rough left over wood (see picture
at right).
Bat houses must be installed at various heights (from 1.8 m to 12.2 m), protected
from the wind and oriented towards the sun in the morning. Different crevices
of different widths, placed at different heights, will attract different bat
species. The entrance should be at the bottom since bats enter from below,
but no obstacles such as tree branches should obstruct it. It may take up to
one year before bats occupy these new structures especially designed for them.
Bats as Visitors
If a bat accidentally wanders into a house through a window, door, or unused
chimney, one should remain calm and not panic. Don leather gloves because a
bat may panic and bite when frightened. Healthy bats have no reason to attack
people unless threatened.
Exclusion methods
To remove a bat from a room, only the doors and windows that allow access
to the outside should remain open. Wait for the bat to follow the fresh air.
Bats usually rest during day time. Therefore, if you want the bat to leave
a room of its own accord, wait until nightfall and make sure the room is dark
enough for the bat to realize it is night. Artificial lights may only confuse
the bat's instinct.
If the first method is unsuccessful, one may consider capturing the bat and
then releasing it outdoors. The bat can be netted or captured in a small box
or can (see above picture). Place the container over the bat, then carefully
slide a piece of hard cardboard under it, ensuring you do not leave any space
for the bat to fly away. These are fragile creatures and therefore should be
handled with care.
Another method consists of using a tube (such as one from a roll of paper
towels). Seal one end and leave the other open. Slowly move the tube into a
horizontal position next to the bat, and often the bat will crawl inside in
an attempt to hide. Then set it free. Once the bat has been removed, you can
seal all possible entry points as stated above.
Diseases Transmitted by Bats
Rabies
Rabies is a potentially fatal viral disease in man and other mammals. It is
transmitted between animals by bites or through contact with saliva or bodily
tissues. Attacks by rabid bats are rare. An individual bitten or scratched
by a wild animal should seek medical attention immediately.
Cats and dogs stand the greatest chance of becoming infected by picking up
a diseased animal. The rabies problem is best managed by having pets and valuable
domestic stock vaccinated against the disease.
An individual spending considerable periods of time in attics, caves, or possible
bat roost sites may consider getting immunized against rabies. Children should
be educated not to handle any wild animal floundering on the ground or a pet
with an unfamiliar behaviour.
A bat found on the ground should be shovelled into a container and transported
to public health authorities for autopsy.
Histoplasmosis
Histoplasmosis is a fungal disease in humans that may be contracted through
the inhalation of dusty bat manure containing the causal organism Histoplasma
capsulatum . A respirator and other protective clothing should be worn
when working in bat roost sites. Most infections are either asymptomatic or
appear as a benign respiratory illness. Bats are not the only source of this
pathogen which is dispersed by wind and can be found in soil and bird droppings
(for example pigeon droppings).
No pesticidal product is registered in Canada for the control of bats.
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