|
|
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.
|
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.
|
Bats and
Migration
By Denise
Tomlinson
|
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.
|
What Do Bats
Eat?
By Brian
Carstens
|
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.
|
|
