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Scientists can actually hear echolocation with a bat
detector. A bat detector takes the ultra sonic sound of the bat,
lowers the frequency, and allows us to hear echolocation. For more
information on how to order a bat
detector see our catalog.
A predator
cruises through the night skies in search of prey, sending out
twenty or more sonar signals per second and
listening for the faint echo of a target. Suddenly, picking up a
return signal it veers for the target. Increasing both the speed
and rapidity of the signals, it locks in on the target and adjusts
its trajectory for the kill. But, the prey has developed a means
of detecting the sonar and begins evasive maneuvers. The predator
increases the signal rate to two hundred or more per second and dives
for the target but at the last instant, in a surprise move, the prey
folds its wings and drops out of sight. The predator swoops by, missing
the target, foiled by the prey’s early detection sophisticated
sonar capabilities, but maybe you didn't’t know that some insects
have developed ears. So far, ears have been found in moths, lacewings
and praying mantises. Research continues and ears may also be found
in some species of beetles, another food source for bats. The ears
developed by these insects are quite primitive, containing only a
few nerve cells each where our ears and the ears of bats contain
thousands of nerve cells. Research so far indicated that these ears
were developed primarily to detect the high pitched sonar of bats
and are used for little else by the insects.
Although
the ears of the insects are not as sophisticated as the bats’, they can hear the bats’ echolocation
calls well before the bat can hear the returning echoes.
The tiger moth has developed an even higher-tech defense
strategy than just mere escape. Located on the surface of the moth
near the ear are tymbal organ made up of a services of grooves in
the chitin (the hard material that forms the exoskeleton of insects).
This area can be flexed or buckled by muscular tension causing a
series of high frequency clicks which closely resemble bat echolocation
calls. When these moths detect a bat in pursuit, they issue a series
of ultrasonic sounds in return which either startles the bat, confuses
it or interferes with its reception of the echoes. If the bat has
never eaten a tiger moth before it will behave as though it had been
startled by the unexpected sound and bolt away.
Written by George Marks whom is the president of the
Florida Bat Center in Punta Gorda, Florida. The Florida Bat Center
is a wonderful organization dedicated to bats in Florida. If you
would like more information please contact George or Cyndi at (941)
637-6990.
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The
Origin of Bats
By
Brian Carstens |
Evolution is a word saturated with meanings. To some
it connotes a progressive diversification of life culminating with Homo
sapiens, to some the development of a system or an idea. Charles
Darwin described the process as “descent with modification”,
and modern biologists define evolution as change with continuity
in successive generations of organisms. We know that all animal populations
change as time progresses, and that this change is often dictated
by the environment. Each newborn generation sees a certain percentage
of it’s members live to reproduce. Most of the time the individuals
who survive to reproduce are simply a matter of chance, but sometimes
an individual wins the genetic lottery and is born with a combination
of traits that give it an advantage. If these traits lead to the
production of a greater than average number of offspring these advantageous
traits will be passed on, and over a number of generations will become
common in the population. This process is know as natural selection,
and it drives evolutionary change.
Today there are hundreds of species of bats, belonging
to the single order Chiroptera. As mammals they came from a long
lineage of animals that arose from the Therapsid reptiles in the
Triassic, some 120 million years ago (mya). They were nocturnal,
insectivorous, and had highly developed senses of smell and hearing.
Most of all they were small, and occupied the fringe niches of a
planet dominated by dinosaurs.
The earliest fossil bat is Icaronyteris index,
and dates from 50 mya. I. index appears to be fairly modern, and
we believe that it could echolocate based on the size and shape of
its cochlea. There are a few other fossils, but most of our knowledge
of bat evolution relies on other types of evidence. We know that
since the time of I. index bats have diversified to fill a wide variety
of niches, and we can imagine how bats like I. index changed
over time to become the species of today.
The more interesting problem is determining the evolutionary
history of bats before I. index. Molecular studies that compare
the percentile difference in the DNA of different species of bats
estimate that the difference between the two suborders of bats is
the same as the difference between most orders of mammals. Orders
like rodents and primates began to speciate 80-65 mya, and we can
speculate that bats got a head start on these. At this time we can
not know for sure, but a safe guess is that bats were around to watch
the extinction of the dinosaurs 65 million years ago.
Evolving the ability to fly required a complex change
in anatomy of the animals that became bats. Most researchers believe
that bats and primates evolved from arboreal insect eaters, and that
bats went through a gliding stage. The wings of bats can be thought
of as two sections, the membranes supported by the arms and the membrane
supported by the fingers provides the thrust and maneuverability.
We can speculate that the membrane in the arms evolved first, and
this would have been sufficient to glide from tree to tree with.
For arboreal animals gliding uses less energy and is safer than climbing
down the tree, crossing the ground between trees, and climbing back
up another tree. Types of lizards, marsupials, and squirrels have
all evolved gliding membranes. Bats would have preyed on insects,
and animals that could control their direction would have had a selective
advantage so the hand wings that define the Chiropterans would have
evolved rapidly. Flight probably evolved before sophisticated echolocation,
but it is clear that the latter was evolving early on in the history
of bats and that this ability facilitated the diversification of
bats into the hundreds of niches that they occupy today.
Written by Bryan Carstens, an OBC volunteer,and a MSU
graduate who focused heavily on evolutionary biology. He is now in
graduate school continuing his studies on bats.
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Bats
and Migration
By
Denise Tomlinson
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Where bats
live is dependent on the availability of food. When the food supply
declines, usually due to weather, bats
have two options. They can hibernate to pass through the low or non-existent
food supply period, or migrate to a place with a more abundant food
supply. In some areas, bats will also do a combination of both. Migration
involves two parts. Movement from one location when food is scarce
and the return to that same location when the abundance of food returns.
There is no clear distinction between migrating bats and hibernating
bats. Some bat species, like the silver-haired bat, migrate and hibernate.
The same is true for red bats. Red bats migrate from the northern
portion of their range and hibernate in the southern portion of their
range. Most temperate bat colonies start dispersing in late July
as young begin flying. In August, most are in the process of migrating.
Most North American bats travel less than 483 km to hibernate, with
the most common distance traveled is 322 km on the North - South
axis. Few temperate bat species migrate to tropical or equatorial
regions. Some bats also migrate up and/or down in altitude as food
supply changes with season. Little is known about the long distance
migration habits of most of our common bats, like the Mexican free-tailed
and the big brown bats. Some bats that are banded in the United States
migrate south to countries with little or no research collecting
of bats. Information of their final migratory destination is not
known. Principal migrating species in North America traveling moderate
to long distances (300 - 1500 km) include the genera Tadarida, Lasiurus,
Lasionycteris, Leptonycteris, Choeronyteris and Pipistrellus. Some
of these bats travel long distances from northern Canada to the Gulf
states and Mexico. The nectivorous bats, like Leptonycteris and Choeronycteris
species follow the availability of food by migrating with the flowering
season. The most documented long distance migrating bat is the Mexican
free-tailed bat (Tadaria brasiliensis). This bat ranges from Oregon
to south Mexico. Bats in the northern California/Oregon region are
non-migratory, spending inclement weather in torpor or hibernation.
Bats of this species in the eastern Nevada, western Arizona and Colorado
regions are non-migratory as well, however do not hibernate. Mexican
free-tails from southeastern Utah and southwestern Colorado migrate
to western Mexico. The most well known colonies, like Carlsbad Cavern
and the caves in Texas and southeastern United States migrate to
eastern Mexico. Some Myotis species also migrate to winter roosts
traveling over shorter distances. Their migration is not necessarily
in latitudinal direction. These bats may travel in any direction
depending on the location of the hibernaculum. Little brown bats
(Myotis lucifigus) migrate from 200 km to 800 km in distance between
summer and winter roosts. Gray bats (Myotis grisescens) migrate several
hundred square kilometers from northern Arkansas hibernaculum to
Kansas, Missouri and Oklahoma. Most records of big brown bat migration
distances are less than 40 km in distance however, there have been
exceptional distances of 230 km recorded. Tolerance of colder weather
may be one reason for the short distances. In general, tree roosting
bats are migratory since trees do not provide enough shelter for
the winter. Hoary bats from all areas migrate more equatorially and
are found below 37¡ Latitude during the winter. Both Lasiurus and
Lasionycteris species are sometimes found in migrating groups, sometimes
accompanied by migratory birds. Long distance flights consume a lot
of energy. Bats that migrate lose about .5 g per 100 km traveled.
Navigation must be accurate and flight efficient. Migrating bats
are known to use vision, echolocation and the sun as orientation
and may use other factors as well, but these have not been studied.
Not only are the energy demands of migration costly, other threats
to the bat's survival are more likely during migration. Adverse weather,
higher chance of predation and disease are all factors that the bat
may face. Accidents during migration such as running into buildings
with wind gusts also happen. Another threat to migratory bats are
pesticides. Pesticides are stored in the body fat over the course
of the summer as the bats eats insects exposed to pesticides. When
the body fat is burned during migration, resins are released into
the bloodstream and may cause illness or death.
Written by Denise Tomlinson, director of Bat World
Everglade and wonderful organization in Florida dedicated to saving
bats. For more information go to batworld.org.
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What
Do Bats Eat?
By
Brian Carstens
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Bats are successful throughout the world due in large
part to their proficiency as predators of all night flying insects.
Between 60 and 70% of all bats are insectivores. Almost any insect
that is active at night can be food for a bat, including moths, beetles,
flies, crickets, gnats, mayflies, wasps, and mosquitoes. There are
other bats that eat a wide variety of food: scorpions, fish, fruit,
pollen, spiders, arthropods, nectar, small mammals, and non-flying
insects. Ten species of bats in Central America are carnivorous,
and they prey on small birds, small mammals, or other bats. One of
these bats, the false vampire Vampyrum spectrum, hunts for its avian
prey using its excellent sense of smell. Other carnivorous bats hunt
by listening to prey generated sounds. These bats also eat a significant
number of arthropods, so it is likely that the carnivorous bats evolved
from insectivorous ancestors. One genus of bats, Noctilio, trawls
for small fish over the water. It uses its hind legs and specialized
toe nails to snag the unsuspecting fish and then returns to a roost
to feed. There are three bats that feed on blood. These are the famous
vampire bats, whose foraging habits are responsible for giving many
other bats a bad name. Some bats eat plant material. In the Old World
the entire suborder Megachiroptera eats fruit and nectar, and in
the Americas the Phylostomidae (of the suborder Microchiroptera)
are also frugivorous. In general, frugivorous bats tend to be larger
than nectivorous bats. They have a more developed sense of smell
and vision, and many roost in trees rather than caves. Frugivorous
bats play a major role in the overall health of the tropical forests.
They disperse the seeds of the fruit they eat which helps the forest
regenerate after being cut down. The plants that rely on bats for
seed dispersal usually have a strongly odored fruit that remains
on the tree long after they are ripe. Often this fruit is on long
stalks or positioned away from twigs and leaves. This allows for
easy access for the bats, but makes it very difficult for birds to
eat the fruit. The seeds of these plant are hard kernels that separate
easily from the flesh of the fruit. Several species of bats are also
important pollinators. There are more than twenty genera of plants
that rely on bats to pollinate them, These plants range from blooming
cacti to wild banana trees. The bats and plants have exhibited modifications
which increase the success of feeding and pollination. Nectivorous
bats have long muzzles and long protruding tongues that have a brush
tip that gathers pollen quickly and efficiently. Flowers of the plants
pollinated by bats angle downward, and shaped and sized just right
for a bat to insert their head and shoulders. In fact, recent research
has suggested that some flowers in the New World are shaped to reflect
the echolocation calls of foraging bats so that they can find the
pollen of that flower. Most have an abundance of nectar, open at
night and have a strong smell. Bats are extremely important members
of a healthy rainforest, and by dispersing seeds they help to regenerate
the forest after clear-cutting or fires. Every ecosystem is integrated
in a similar manner, with each part depending on other parts of the
ecosystem and being depended on in turn. Ecologists are concerned
about the loss of biodiversity because we know that the loss of any
species will effect all the other species in the ecosystem.
Written by Bryan Carstens, an OBC volunteer,and a MSU
graduate who focused heavily on evolutionary biology. He is now in
graduate school continuing his studies on bats.
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