The elephant´s vision
The elephant´s eyes are quite small If one compares them with their body
dimensions. Their sense of vision is moderate, as they lean more on their
olfactory and auditory senses instead. The eyes of an elephant are located
on the sides of the head and therefore provide better peripheral vision,
rather than binocular vision. Elephants (and especially African Forest
elephants) have long eyelashes to protect them from the blowing sand, dirt,
debris and the dense vegetation:In addition to the upper and lower eyelids,
and like many other animals, all elephants species have a third eyelid (the
so-called nictitating membrane, from latin nictare, to blink) which moves
horizontally across the eye, and which works for moisten and protection
when bathing or dusting. Some elephants develop a white ring that
encircles the iris as they mature. This ring is similar to an age-ring that
may develop in humans (as they age) called arcus lipoids, and does not
affect vision.
Elephants are dichromatic; they have two kinds of color-sensors
in their retina, one type of cones for *reds and another for greens. That
means that they are "color-blind" when you compare them to humans (we are
trichromatic: we have three kinds of cones: red, green and blue). What is
also interesting is that they are one of the animals that exhibit
arrhythmic vision, that is, their vision changes within the daytime. At
night, their eyes are most sensitive to violet light so they can see pretty
well under the smallest amount of daylight when the prevailing colour of
the atmosphere is in the violet range. They have pretty sensitive rods as
well (the higher density of rods in the retina, the more sensitive to light
one can be), so elephants do a good job when it comes to night vision
compared to humans. The eyesight of the elephants is thought to reach a
range of about 46 m. However, this can vary and be much shorter, probably
because elephants use their vision sense less than their olfactory and
auditory senses. When they focus on their vision, however, they show to
react to the smallest ear movement of another elephant placed up to 50 m.
in the distance.
The elephant eyes are amazingly beautiful, and like humans, they
can show different colours; the four most common eye colours are dark
brown, light brown, honey and Gray, but there are more tones like:
blue-Gray, gold, brown tones, green and yellow, and even the right and left
eye of one elephant can be differently coloured.
Elephants have good hearing, detecting sounds as low as 14 to 16 hz (human
low range: 20 hz) and as high as 12,000 hz (human high range: 20,000).
Elephants frequently use infrasonic sounds, which are sounds emitted below
the human hearing range, in long-distance communication. Research has shown
that elephants are capable of recognizing calls and voices of particular
individuals from 1 to 1.5 km (0.6-0.9 mi.) away. Refer to Communication
Section. The ears of the elephant are used to funnel in sound waves from
the environment, contributing to its keen sense of hearing. In general,
animals with large heads and wide-set ears are better adapted for hearing
lower frequency sounds because the larger skull encompasses longer ear
canals, wider tympanic membranes (membrane that separates the middle ear
from the exterior), and larger middle ears.
References: Murray E. Fowler, Susan K. Mikota (2006): Biology, Medicine,
and Surgery of Elephants
Touch
Elephants are very tactile in nature. Elephants use all parts of their body
to interact with one another in all forms of behaviour, including
parental-offspring, playful, aggressive, defensive, exploratory, sexual,
and anti-predator.
The trunk is one of the most tactile appendages elephants have. It is used
to stroke, touch, explore, caress, or reassure in care-taking and may also
be used to slap or block in defence or dominance situations.
The trunk is so sensitive to touch that it is capable of perceiving
pressure differences as light 0.25 mm (0.01 in.) in depth, which is
equivalent to a light brush against the skin.
The strength of an elephant’s trunk is capable of lifting weights in excess
of 250 kg (550 lb.).
Elephant trunks have extensive sensory motor cells, called Pacinian
corpuscles, that enable them to have a strong sense of touch. The pacinian
corpuscles are composed of concentric membranes of connective tissue,
similar to the layers of an onion. Between each layer of connective tissue
is a slimy gel. When a movement or vibration is detected, the pressure
deforms the gel and connective tissue layers of the Pacinian corpuscles.
This stimulates nerve endings and sends a signal to the brain.
Pacinian corpuscles are also found in the soles of elephant feet, assisting
in the detection of seismic vibrations (shaking, vibrating movement of the
Earth).
Many animals including elephants survived the Asian tsunami in 2004. It is
thought these animals had advanced warning to the tsunami due to their
detection of seismic vibrations. The tsunami’s approaching vibrations were
detected by the Pacinian corpuscles in the elephant’s feet and alerted them
to the approaching storm.
K Rajaram IRS 11225
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