KPOV – The Point
Gardening: Get Good At It
Bats
October 27, 2015
Bats in the belfry; bat out of hell; blind as a bat; just plain batty?
The news media, movies, television, and comic books often perpetuate myths, “oldwives-tales,” folklore, legends, and fears about bats that a surprising number of people
believe. Bats do not get into your hair, they are not flying mice, they don’t come “out of
hell,” they are not blind, and only three species in Central and South America make a
diet of blood.
Myths about bats are found in many human cultures. Bat gods were important to many
pre-Colombian civilizations in Central America, and bats are used in voodoo worship in
parts of Africa as well as in many parts of the Caribbean today. The writings of William
Shakespeare, Robert Louis Stevenson, and others have contributed to legends that cast
a veil of fear on people, as they associate bats with graveyards, death, ghosts, and
goblins. The association of bats with the legend of human vampires has an uncertain
origin, but since the time of Cortez and his Conquistadors, peoples of western civilization
have linked vampire bats with the legendary “human” vampires of Transylvania. The
ancient Egyptians believed that bats could prevent or cure poor eyesight, toothache,
fever, and baldness, and a bat hung over the doorway of a home was thought to prevent
the entry of demons that carried these “diseases.” To the Chinese, bats are regarded as
symbols of happiness and good fortune (health, wealth, serenity, virtue, and long life). At
one time Chinese mothers would sew small jade buttons in the shape of a bat on the
caps of their babies, a custom believed to impart long life. Ancient and modern-day art
objects, tapestries, Imperial robes, home furnishings and the like often include bats as
part of the motif.
Bats belong to the mammalian Order Chiroptera, meaning “hand-wing.” Some members
of this group of flying mammals have existed (in their present form) for at least 50 million
years. Approximately 1,116 different species are known world-wide, representing
approximately 20% of mammal species of the world. Bats are second only to rodents in
number of species and they probably outnumber all other mammals in total numbers.
Bats are distributed on every continent except Antarctica and they are found on many
oceanic islands. The overwhelming number of species live in tropical regions. 44 species
are known to live on the North American Continent, north of Mexico. Adult bats found in
North America range in weight from approximately two grams (0.07 ounces) with a wing
span of about 10 centimeters (4 inches), to those weighing over one kilogram (2.2
pounds) and having a wing span of nearly 1.5 meters (6 feet). The skeletal features of
bats are comparable to those of humans and most other mammals. Unlike most birds
which have hollow bones, the bones of bats are typically small and delicate. The bones
of the wings are lengthened to provide support for the wing membranes. A highly
resilient double membrane stretches between the elongated fingers, attaches to the side
of the body, and extends to the ankle.
Bats are friendly, useful creatures that you can enlist during the warmer months to help
you control pesky insects in your backyard. The fact is that bats are actually quite
harmless and are important indicators of a healthy environment. Because bats are
sensitive to high pollution and pesticide levels, they are useful as a warning sign to
potential environmental problems. Bats can also be important weapons in combating
insects that can be harmful to humans as well as gardens. Aerial insectivorous bats are
drawn to insects, such as moths, flying around lights. Alternatively, some bats are
insectivorous gleaners, and hunt by capturing insects off the ground or from vegetation.
The prey of insectivorous gleaners includes crawling arthropods (centipedes, scorpions,
beetles, etc.), grasshoppers, katydids and the larvae of certain crop pests. Regardless of
their feeding style, there can be no understating the fact that insectivorous bats are a
benefit to pest management programs! A single little brown bat can eat up to 1000
mosquitoes in a single hour, and is one of the world's longest-lived mammals for its size,
with life spans of almost 40 years. While most insect-feeding birds are active in daylight,
bats have perfected a feeding strategy that targets night-flying insects. Moths and
mosquitoes may be their mainstay, but they also feast on insects ranging from gnats,
biting midges, leafhoppers, crickets, termites, flies, spiders, grasshoppers to large flying
beetles. Bats will consume from a quarter to half their body weight in insects each night.
While bats in other parts of the world feed on fruit, fish, nectar, or even blood, all Oregon
bats dine on insects. They consume pests such as spruce budworm moths, tussock
moths, mosquitoes, pine bark beetle moths and gypsy moths. Bats clear bugs out of
your garden in a secondary way, too- many insects can hear the bats and leave the area
to avoid being eaten. So, more bats equals less bites on you and more broccoli in the
garden. Studies conducted in Kansas and Canada over the last few years have shown
that bat populations can effectively control corn rootworm moths, thus reducing and even
eliminating the need for agricultural insecticide applications in some areas. If bats can
effectively control insects on such a large scale, just imagine what they can do in your
garden.
Nectivorous bats feed on pollen and nectar. As they move from one plant to the next
they provide valuable pollination services (similar to bees). They feed on pollen and
nectar, and are critical to the pollination of columnar cacti (saguaro, organ pipe) and
agaves. In Mexico they also feed on the fruit of these plants, ultimately aiding seed
dispersal by transporting seeds in their feces. Biologists calculate that the pollination of
agaves and various cacti would drop approximately 97% without our nectivorous bats!
What a bat eats must come out. Bat excrement, also known as guano, has no odor and
typically contains 10 percent nitrogen, 3 percent phosphorus, and 1 percent potassium.
Guano can make your soil more productive, and it has no fillers, as other types of
fertilizer often do. This natural plant enhancer benefits flowers, ornamentals, vegetables,
and herbs. It is also extremely long-lasting in most types of soil.
Bats use roosts for different reasons based on the time of day and the time of year.
Roost types include the day roost, night roost, maternity roost, and hibernation roost.
During the day, bats typically want protected roosts that are free of disturbances and
predators, and which provide dark, quiet conditions where they can rest for several
hours. Day roosts are usually 10-15’ above ground, and can be as many as 30 miles
away from foraging grounds and water sources. At night, however, bats feed and roost
intermittently so they choose roosts that are in convenient proximity to their foraging
grounds. Trees, porches, and even abandoned bird nests are common examples of the
temporary roosts used by bats while feeding at night. Where bats forage may change as
weather conditions and insect populations change; hence, these fleeting nighttime roosts
are easily abandoned for more convenient ones. Bats will aggregate seasonally to form
maternity colonies in spring (the largest groupings of bats) and winter colonies for
hibernation. In both types of seasonal roosts, bats seek dark, climate-controlled
environments. Females will select a maternity roost based on high temperature
conditions: upper 70s to 95 deg. F. Roost temperatures higher than this may cause
death of the young. Bats have a very high fidelity to their maternity roost. Like pigeons
and doves, they will return to the exact location each spring to rear their young
After the maternity colonies disperse – late summer to early fall – bats may be found
roosting on protected or quiet exterior walls of buildings. These are migratory or transient
bats, and their presence does not necessarily indicate a permanent colony. The
presence of these bats is usually short term. As the season progresses and food
sources change, they will move on. Similar sightings of bats on building walls may also
occur following inclement weather (i.e., rain and wind). Often these bats are simply
disoriented and in need of rest; they likewise move on within a matter of days.
With few flying insects available to them during winter in Central Oregon, bats survive by
hibernating, migrating to regions where insects are available, or a combination of these
strategies.
During hibernation, metabolic activities are greatly reduced—a bat's normal body
temperature of around 100 degrees F is reduced to just one or two degrees higher than
that of the hibernaculum, and their heart rate slows to only one beat every four or five
seconds. A hibernating bat can thus survive on only a few grams of stored fat during the
five- to six-month hibernation period.
Banding studies indicate that little brown bats will migrate 120 miles between
hibernacula and summer roosts, and, if undisturbed, they occupy the same site year
after year. They select areas in the hibernaculum where there is high humidity (70–95
percent), and the temperature is 34 to 41 degrees F. Still, there are some species, such
as the big brown bat, that can hibernate in relatively exposed situations in buildings
where there is considerable fluctuation in temperature. It is important not to disturb
hibernating bats. If a bat rouses early from hibernation, it must use its fat reserves to
increase its body temperature. A single disturbance probably costs a bat as much
energy as it would normally expend in two to three weeks hibernating. Thus, if disturbed
multiple times, hibernating bats may starve to death before spring.
White-nose Syndrome (WNS) of bats is a disease caused by the fungus
Pseudogymnoascus destructans (formerly known as Geomyces destructans). The
disease is estimated to have killed over seven million bats in the eastern United States
since 2006, and can kill up to 100% of bats in a colony during hibernation. Although it
has not been found in Oregon to date, the fungus and disease are spreading across
North America towards the West and into Canada.
The fungus grows on the noses, wings and ears of bats during winter hibernation, giving
them a white, fuzzy appearance. The fungus invades the deep skin tissues and causes
extensive damage. Affected bats arouse more often during hibernation which causes
them to burn up their crucial fat reserves needed to sustain them through hibernation,
leading to starvation and death. Additional causes for mortalities may include impairment
of physiological processes due to wing damage, including reduced circulatory and
thermoregulatory abilities, reduced gas exchange capabilities, and dehydration. Humans
have the potential to spread the fungus to new locations when it may attach to clothing
and gear used in caves, mines and roosts. Those who visit bat roosts, caves, and mines
are strongly urged to decontaminate all clothing and gear afterwards by using
appropriate cleaning and disinfection protocols. If there’s no cure found for White-nose
Syndrome, many scientists fear that bats will be extinct within a few decades.
Ready to welcome these misunderstood beneficial predators into your yard? Adding
late-day or night blooming plants to your garden will increase your yard appeal to bats.
Try moonflowers, honeysuckle, or evening primrose. Adding a simple wooden bat house
to your yard will also offer bats a safe place to roost without the need for cave or belfry.
Since there are plenty of insects in most gardens to provide their favorite entrée, all we
need to supply is water and shelter. Bats need a clean and accessible water source. In
the wild, most bats swoop down over the surface of open bodies of water such as lakes,
ponds, or slow-moving streams to take a drink. A garden pond with short plants on
opposite sides is an excellent water resource for bats. They may also use raised
birdbaths that are located in an open space.
You can offer them shelter by installing a bat house. Bat house sizes range from holding
a dozen or so bats to having enough space for a colony of 500 bats. Most North
American bats prefer to live in large groups, called colonies, so a mid-sized house (100300 bats) is typically recommended. A bat house may be mounted on a tree, pole, or
building; however, houses mounted on poles or buildings tend to have a slightly higher
occupancy than those mounted on trees. For mounting on buildings, wood or stone
buildings are best, and your bat house should be mounted under the eaves with some
sun exposure. You should mount your house 15-20 feet above the ground where it will
not be exposed to bright lights. Temperature is also a consideration. You should place
your bat house where it will receive at least six hours of sun.
Bats in your belfry? It’s a good thing.
Resources:
Bats - Defenders of Wildlife.org
Bat Facts and Folklore – BU Center for Ecology and Conservation Biology
Smithsonian Institution National Museum of Natural History
Little brown bat – biokids.umich.edu
Batty About Bats – University of Arizona
Living with Wildlife (Bats) – Washington Dept. of Fish and Wildlife
Bats in and Around Structures – Univ. of Nebraska – Lincoln Extension
Living with Wildlife (Bats) – Oregon Dept. of Fish and Wildlife
Wildlife Health (White Nose Syndrome of Bats Fact Sheet) – Wash. Dept. of Fish and
Wildlife