...awarded
to our website!
|
Senses
of the Black Bear
Do
bears have very poor eyesight?
Bears
actually can see fairly well —
at least as well as humans. Polar bears have the
best vision with special adaptations that allow them to see underwater
and to filter snow glare. The eyes of an American black bear are small,
round, widely spaced, and forward facing. American black bears have color
vision and seem particularly sensitive to blue and green wavelengths.
They may even be sensitive to red — if this is true, then black bears
would have the same color vision that humans do. The ability to see colors
probably helps them find food, since much of their diet consists of colored
berries and fruits. They also have binocular vision that allows for good
depth perception. However, they are nearsighted, so they have difficulty
distinguishing objects at a distance. Nearsightedness probably is an advantage
as they forage close to the ground, and it also is responsible for their
ability to see moving objects far better than stationary ones. Cubs are
born with blue eyes which change to brown during their first year (except
albinos, which lack any color pigment at all). Finally, a bear's eyes
are reflective and mirror the moonlight. Like most nocturnal animals,
bears have a reflective layer, called the tarpetum lucidum, lining
the back of the eyeball. This layer reflects light back through the retina,
allowing the light to stimulate the rods a second time, this improving
night vision.
How
well can bears hear?
It
is often difficult to determine the answer to such a question because
we are not able to test an animal's hearing in the same manner we would
a human's. It is believed that black bears hear much better than humans,
probably in the ultrasonic range. It is interesting to note, though, that
the structure of a bear's ear is unique compared to that of its fellow
carnivores. The middle ear consists of a balloon-shaped, bony structure
that forms a resonating chamber around the ear drum. These structures
are call the auditory bullae and they increase hearing sensitivity.
This balloon-shaped structure is formed by the fusion of two bones —
the entotympanic and the ectotympanic. In
most carnivores, the entotympanic bone is larger and forms most of the
chamber wall. In bears, this is reversed. The entotympanic is reduced
and is actually invisible when viewed from the outside, and the ectotympanic
becomes more prominent. Whether this increases or decreases hearing ability
is still unclear.
Is
it true that a bear's sense of smell is 7 times greater than that of a
bloodhound?
Indeed
it is. There is perhaps no other animal with a keener sense of smell.
Bears rely on their sense of smell to locate mates, detect and avoid danger
in the form of other bears and humans, identify cubs, and FIND FOOD. Although
the region of the brain devoted to the sense of smell is average in size,
the area of nasal mucous membrane in a bear's head is one hundred times
larger than in a human's. This gives a bear a sense of smell that is 7
times greater than a bloodhound's. In addition, they have an organ called
a Jacobson's organ, in the roof of the mouth, that further
enhances their sense of smell.
Here are some accounts of how truly well a bear can smell:
"A
black bear in California was once seen to travel upwind three miles in
a straight line to
reach the carcass of a dead deer."
". .
. male polar bears march in a straight line, over the tops of pressure
ridges of uplifted ice . . .
up to 40 miles to reach a prey animal they have detected."
"A
bear has been known to detect a human scent more than fourteen hours after
the person passed along the trail."
"A
male can detect which way a breeding female is traveling just by sniffing
her tracks."
Quotes are from The Great Bear Almanac by Gary Brown
Bears
use this keen sense of smell to communicate with each other. By leaving
their scent on trees and vegetation, they are broadcasting their presence
to other bears that may be in the area.
This
keen sense of smell is why you should always be bear
aware when living or recreating in bear
country. For suggestions on living in bear country, click
here. For tips when camping or hiking in bear country, click
here.
|
