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Manatees have a large digestive system, and unique,
continuously replacing molars, to cope with an
herbivorous diet. The manatee eats abrasive plants that
wear down these molars. As an adaptation, new molars
form at the back of the jaw and move forward, pushing
out the oldest and most worn teeth. How fast these new
teeth grow depends on how much fiber is in the plants
that they eat. Manatee's small eyes have a 'nictitating membrane',
a sort of clear lens,
that can be drawn across the eyeball for protection.
Manatees have fairly good visual acuity and can
distinguish between different-sized objects, different
colors and patterns. Manatees emit sounds underwater
that are believed to be used in communicating with one
another, like a conversation.
Vocalizations may express fear, anger, or sexual
arousal. They are also used to maintain contact,
especially when manatees are feeding or traveling in
turbid water. Especially common are the vocalizations
between cow and calf. Adult manatees move through the water
primarily by the pumping action of the tail. The front
flippers are used for steering and lateral movement,
crawling over the water bottom, or for putting
food into the mouth). Young manatees even seem to propel
themselves with their flippers.
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Manatees do not
form permanent pair bonds. During breeding
session a
single female, or cow, will be followed by a
group of a dozen or more males, or bulls,
forming a mating group. Although breeding and
birth may occur at any time during the year,
there appears to be a slight peak in the spring
session in calve birth. Manatees usually bear one calf although
twins have been recorded. Intervals between
births range from three to five years (a two
year interval may occur when a cow loses a calf
soon after birth.) The gestation period is
approximately thirteen months. Mothers nurse
their young for a long period and a calf may
remain dependent on its mother for up to two
years. The cow assumes total responsibility for
raising the calf without the bull. Calves nurse
under water from a nipple located behind the
cow's flipper and begin to eat plants a few
weeks after birth. Scientists believe females do
not become sexually mature until five to nine
years of age. They live long lives- it is
believed that manatees are capable of living 60
years or more, but because of the many
perils in the wild, longevity is uncertain.
Because the reproductive rate is so low, the
species as a whole adapts very slowly to
changing situations or unnatural stress. The
current population is estimated to consist of at
least 1,200 animals. The manatee was officially
declared endangered in 1973, as part of the
original endangered species listing for the
Federal Endangered Species Act.
Ultimately,
the loss of habitat is the most serious threat
facing the manatee today. Florida, the fourth
most populous state in the nation, is
experiencing unprecedented growth. Nearly 1,000
people a day move to Florida, with over 80%
settling near waterways. The growth in human
population with its added pollution, litter and
boat traffic, has degraded and/or eliminate the
manatee habitat. Many fresh water and marine
grass beds have been lost due to water
pollution, herbicides, surface runoff, propeller
dredging, and dredge and fill projects. There
are very few places left where the manatee is
free from the danger, stress and harassment
posed by human activity. |
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