Nile Crocodile Distribution:
The Nile Crocodile is widely distributed throughout
Africa, but more so in Central and West Africa where it is estimated
that about two-thirds of the continent's crocodiles live. It is
thought that there are between 250,000 to
500,000 living in the wild in Africa's fresh water marshes, lakes and
rivers. They can be found in: Angola, Benin,
Botswana, Burkina Faso, Burundi, Cameroon, Central African Republic,
Chad, Congo and DRC, Egypt, Ethiopia, Equatorial Guinea, Gabon,
Gambia, Ghana, Guinea, Guinea Bissau, Ivory Coast, Kenya, Liberia,
Madagascar, Malawi, Mali, Mozambique, Mauritania, Namibia,
Niger, Nigeria, Rwanda, Senegal, Sierra Leone, Somalia, South
Africa, Sudan, Swaziland, Tanzania, Togo, Uganda, Zambia and
Zimbabwe.
The Design Features:
Nile Crocodiles usually grow to about 5 meters
(16.4ft) in length.
A fully mature male can weigh 700kg (1,500lb). However, there are
known cases of them reaching 6m (19.7ft) in length.
The skin of the young is quite brightly marked as
can be seen below in the photos. The colours change as the juveniles
reach maturity. The adult skin is scaled and grey brown in colour
having yellow patches making for extremely good camouflage.
They have four short legs with clawed feet. Crocodiles usually
crawl, but can raise up and sprint for short bursts of up to 14km/hr
(8.7mph). The long powerful tail can propel them through water up to
similar speeds, but for much longer duration. The tail is also used
for steering and for 'barrel rolling' when twisting and drowning
their prey. There are two rows of horney scales (ossified scutes) that run along the back
and well onto the tail section where they converge forming a single
row.
Crocodile's nostrils, eyes and 'ears' are situated
on the top of the head which allows their bodies to be submerged,
and virtually hidden, while they stealthily approach their prey
undetected.
Their eyes have vertical pupils that open
wide in low light allowing them to be good night-hunters. They
have tear glands for cleansing and a nicitating
membrane that slides over the eye for protection. Crocodiles have excellent hearing
ability.
Unlike other present day reptiles, Crocodiles
have an efficient four-chambered heart, similar in operation to
that of mammals and birds. Their normal dive period is only for
a few minutes, but when threatened they can stay submerged for 30
minutes and even up to 2 hours while going inactive which
lowers their metabolism. They are cold blooded ( ectothermic ) and
sun-bathe to raise their temperature and lay in shade or water to
cool down.
Crocodiles are Thecodonts having between 64 to 68
conical shaped teeth. The upper jaw ( Maxilla ) has 10 frontal (
Premaxilla ) teeth and further 13 or 14 rear teeth on either side. The lower jaw ( Mandible
) has the remaining 14 or 15 teeth on either side. The 4th tooth of the lower jaw
fits neatly into a 'pit' in the upper jaw and remains visible when
the mouth is closed.
Their extremely strong jaws are designed for
crushing, but once closed do not require much force to hold them
shut. They have no tongue, instead having a gular
throat pouch that when activated blocks water, so they can
chew their food while submerged.
Crocodiles are thought to live to the age of about
70 years.
Reproduction:
Under normal conditions males become sexually mature when they reach a length of about 3m (10ft)
and females at
about 2 to 2.5m (6.5 to 8ft).Given normal conditions this length can
be achieved in about 10 years. Egg laying takes place 2 months after
mating. Nesting takes place in November or December. In north Africa
this is the dry season, while south of the equator it is the rainy
season. The females lay clutches of between 25 to 70 eggs in nests
about 2m from the water's edge and 500mm (20") deep in the sandy
river or lake banks. The average clutch is about 50 eggs of which
the mother guards for the incubation period of 3 months. The male
crocodile will often stay quite close by and both parents will
attack any would be intruders. Their are times when the parents do
have to leave the nesting area to cool down and this is the time
when nests can be raided by monitor lizards, small animals and even
humans.
The sex of a Nile
Crocodile is subject to Temperature Sex
Determination ( TSD ). This means the sex of a hatchling is determined
by temperature and not genetics. During
the middle of the third period of incubation - if the temperature of the nest
remains within the 3 degree Celsius zone
of 31.7 to 34.5 (89.1F to 94.1F) the result will be Male. Should the
nest temperature fall either below or rise above this zone the
result will be Female.
Hatchlings
are about 30cm (1ft) in length. They will stay with their mother for
about 2 years at which time they will have grown to about 1.2m
(4ft). Now large enough to hunt and defend themselves they will
establish new territorial areas away from and without disturbing the
older and lager crocodiles.
Crocodile Eating Habits:
Crocodiles can eat up to half of their body weight,
and then go for long periods without eating. They are not too choosey about
their diet which can include: amphibians, aquatic
invertebrates, birds, carrion, fish, mammals, reptiles and
people.
Acknowledgements and further reading: W1, W3
