Newsletter 70
14/05/13
“Mirror
Mirror on the Wall, Who has the Best Eyesight of
them All?"
Hello Friends
I am following a female cheetah which is hunting
in Kenya's Masai Mara. Suddenly she elevates onto a termite mound
and then starts to run, not at full pace but at a quick pace. We
follow in our film cars for about 1km and come on a newly
born Thompson's gazelle fawn lying in the grass. The cheetah walks
back and forth and almost steps on the fawn before finding it. After
playing "cat 'n mouse" with the fawn, the cheetah carries it into
the shade and eats it.
Later I return with Elmon Mhlongo a shangaan
tracker and Lakakan Sukuli, a Masai, to the place where the cheetah began her
run. I place a dummy fawn in the grass where the gazelle fawn was
hiding and challenge Elmon and Lakakan to see it. None of them are
able to see the dummy.
After giving Elmon and Lakakan a set of 8 ply
binoculars, they could see, at a distance of 1kilometer, the dummy in
the grass.
It is certain that the cheetah saw the flick of the
fawn's ear and then ran closer to locate the fawn. As long as the
prey remain motionless, they can avoid the predator, but the slightest
movement will be detected.
I have seen cheetah walk within feet of a
steenbuck frozen in the grass and I have seen leopard walk within 10
feet of a grey duiker motionless in the bush.
The fur on the cheetah's forehead comes over the eyes, shielding the
eyes from the sun
American baseball players and west Indian cricketers are mimicking
the cheetah tear line to combat the glare
At Londolozi Game Reserve, I am watching a leopard
cub playing in tree. Suddenly the leopard descends the tree and runs
300 metres to a dead leadwood. On the leadwood is a large monitor
lizard, perfectly camouflaged against the bark of the tree. The
leopard cub attacks the monitor lizard which falls to the ground.
Here the monitor lizard shams dead for a full 15 minutes as the
leopard cub rolls and claws it.
The monitor decides on another form of defense.
It bites the leopard cub on the foot. The monitor's jaws clamp in a
vice like grip and the leopard cub is unable to free itself for a
full 40 minutes. There is no doubt that the initial movement of the
monitor lizard attracted the leopard to it from a distance of 300m.
Seen from the side, the leopard is able to detect the slightest
movement, even in low light conditions
I am rehabilitating the lioness Shingalana from a
tented camp on the edge of a dry river bed at Londolozi Game Reserve.
At 10pm I hear the
distress call of a duiker. Shingalana has caught, but not killed a
grey duiker in the dry river bed.
Taking a rifle, I leave my tent to investigate,
but can see nothing in the darkness. I wait several minutes to allow
my eyes to adjust to the dark, but although I can hear the duiker
giving the distress call, I can see nothing. There is no moon and
heavy clouds obliterate the starlight. It is the blackest of nights.
So how did Shingalana see the duiker, let alone catch it in
the darkness?
The reference books will tell you that a lions
night vision is 6 to 7 times better that a human being's. How as a
matter if interest, did the scientists discover that?
The military has developed night glasses which allow me to see the
same as a cat in the dark
The white stripes under the lion's eyes reflect the star and
moonlight into the heavily rodded eyes of the lioness.
Wanting to assist Shingalana with her kill, I
take a paraffin lantern a move to Shingalana's position. What is
obvious is that her iris completely fills her eye. Like the lens of
a camera, it is wide open in the low light. Shingalana's eyes are
rodded and possess a tapetum lucidum which absorbs the available
light.
On this night, there is no light, no moon, no stars nothing!
Did she perhaps use the whiskers which act as sensory organs in the
dark, to locate and catch the duiker, I doubt it.
Lions will use their whiskers as sensory organs on a dark night
The tapetum lucidum gathers the light from the spotlight reflecting
the light backwards. It is the tapetum lucidum and the rodded eyes
which give the leopard seven times better night vision than human
beings
Later I conducted an experiment on a dark night.
I threw Shingalama a soccer ball which was illuminated by a
spotlight, she caught it easily. Then I threw her a soccer ball on a
night with no moon, just starlight, she caught the soccer ball
easily.
Shingalana's forward facing eyes give her excellent judgment when
catching a soccer ball
The human and lion's eyes both face forward. Both are predators. One
numbers 7 billion, the other number about 30 000 in the wilds
The Tigers at Tiger Canyons are most successful
when hunting during electrical thunderstorms, (when the prey's
senses are dulled), or on very dark nights, when darkness allows them
to stalk or ambush the prey. They will not normally hunt when there
is a full moon.
The cheetah on the other hand, will mostly hunt
during the day but will also hunt on a full moon when visibility is
good.
The cheetah's night vision is the poorest of the big cats. They will
hunt on moonlight nights.
So which cats have the best eyesight? For the
best long vision during the day, I'm going for the cheetah, with lion
as the second best.
For the best night vision I'm going for the
individual stalker pouncers, leopard and tiger. I cant split these
two.
The second best cat for night vision, I'm going
for lion. I'm wondering if lions will hunt on a truly dark night.
Being a co operative hunter they would need to know where the other
hunters are, so some starlight maybe necessary. Too much moon and
the prey can detect them. Therefore a dark night for lion with some
starlight maybe ideal.
In terms of night vision I put the cheetah last
of the four big cats. The cheetah's whiskers are small, the tear
line is designed to cut down glare in the day. The small white lines
in the inside of the eye and tapetum lucidum gives night vision
because they need to detect approaching danger on a dark night.
All cats I believe detect the movement first and
then move closer to get the definition of the prey. This is why
nyala, bushbuck mountain reedbuck, kudu, grey duiker amongst others,
will all use the freeze technique to avoid the predator.
Therefore long vision in the daytime, cheetah first, lion
second. Night vision, tiger and leopard first, lion second, cheetah
third.
Please send me any information on vision of big
cats and thank you for all your feedback on "Who is the Fastest of
them All"
Tread lightly on the earth
JV
The tiger eye surrounded by white, geared for night vision
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Additional information:
The
tapetum lucidum is a layer
of tissue in the eye of many vertebrate
animals. It lies immediately behind the
retina. It reflects visible light back
through the retina, increasing the light
available to the photoreceptors, though
blurring the initial image of the light on
focus. The tapetum lucidum contributes to
the superior night vision of some animals.
Many of these animals are nocturnal,
especially carnivores that hunt their prey
at night, while others are deep sea animals.
Eyeshine is a visible effect of the tapetum lucidum. When light shines into
the eye of an animal having a tapetum
lucidum, the pupil appears to glow
Why do different
species of cats have
different pupils?
All big cats and
some small cats
(cougars and lynx)
have round pupils.
But all house cats
and the species they
descend from
(caracals, African
sand cats, etc.)
have vertical,
almond-shaped
pupils.
By day, the
circular pupil
is inefficient
at blocking
light. Pupil
shapes have
evolved that
limit incoming
light, the most
advanced being
the vertical
slit. The slit
pupil can shut
out all light
except a narrow
band. Its
vertical
orientation is
of significance
too, as it works
well with
eyelids. As an
animal squints,
partially
closing its lids
at right angles
to the vertical
slit pupil, it
further reduces
the amount of
light entering
its eye.
Lions hunt by
day and have
circular pupils,
while smaller
cats hunt by
night and have
slit-like
pupils. Their
vertical pupils
help them to
endure the
bright daylight
by restricting
the amount of
light that
penetrates the
lens. Lions are
less concerned
with this and
spend much of
their time
asleep.
The pupil of the
clouded leopard
never gets fully
round like those
of big cats, but
never shrink to
vertical slits .
The Tiger and
cheetah has
round pupils
although the
tiger hunts at
night.
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