Crocodiles

## **Appearance:**

Considerable variation exists throughout the range of the Nile crocodile.

Generally, it is a large crocodilian, averaging 5m in length but reportedly reaching 6m in rare instances.

There are dubious reports of 7m animals having existed, but these are hard to verify.

## **Diet:**

Although the juveniles are generally restricted to eating small aquatic invertebrates and insects, they soon move onto larger vertebrates such as fish, amphibians and reptiles.

Adults, however, can potentially take a wide range of large vertebrates, including antelope, buffalo, young hippos, and large cats.

Fish and smaller vertebrates often form the greatest part of their diet, however they have a reputation as being man-eaters, they have probably killed more people than all other crocodilian species combined.

There is some evidence that Nile crocodiles in cooler countries reach slightly smaller adult sizes (4m).

There are two known population of dwarf Nile crocodiles living on the extreme limits of the species range, in Mali and even the Sahara Desert.

Due to suboptimal conditions, adults average between 2 and 3 metres.

Juveniles are dark olive brown with black cross-banding on the tail and body.

This banding becomes fainter in adults.

Along with hippos and lions, crocodiles account for perhaps a few hundred deaths and disappearances each year, although exact figures are very hard to verify.

Nile crocodiles will also often scavenge from carcasses, together with a number of other animals, all of which seem to tolerate each others presence.

Several prey animals have been found wedged under submerged branches and stones, leading to reports that the crocodiles store unwanted prey here until a later date.

Some claim that it is necessary for the prey to decompose before the crocodiles are able to tear portions of flesh off, but this is unlikely to be true.

The flesh may become softer if the prey remains in water after death, but crocodiles will certainly avoid rotting meat.

When feeding, a number of individuals will hold onto a carcass with their powerful jaws whilst twisting their bodies.

The anchorage provided by the other individuals allows large chunks to be torn off for easier swallowing.

Other cooperative feeding behaviour has been reported, such as the action of many animals to cordon off an area of water to concentrate fish within.

A hierarchy of feeding order is often observed in such situations, with more dominant animals feeding first.

## **Breeding:**

This species digs hole nests up to 50cm deep in sandy banks, several metres from the water.

These may be in close proximity to other nests.

Timing of nesting behaviour varies with geographic location, it takes place during the dry season in the north, but at the start of the rainy season further south, usually from November through to the end of December.

Groups of crocodiles will often move onto land to scavenge from kills made up to several hundred metres from the water.

Adults have also been observed fishing using their bodies and tails to corral the fish towards the bank where they are concentrated and picked up with a sideways snatch of the jaws.

Females reach sexual maturity around 2.

6m, males at around 3.

1m.

Females lay around 40 to 60 eggs in the nest, although this number is quite variable between different populations.

Females remain near the nest at all times.
Incubation time averages 80 to 90 days (ranges from 70 to 100 days), after which females open the nest and carry the juveniles to the water.
Both males and females have been reported to assist hatching by gently cracking open eggs between their tongue and upper palate.
Hatchlings remain close to the juveniles for up to two years after hatching, often forming a creche with other females.
As with many crocodilians, older juveniles tend to stay away from older, more territorial animals.
Despite the vigilance of the female during the incubation period, a high percentage of nests are raided by a variety of animals, from hyaenas and monitor lizards to humans.
This predation usually occurs when the female is forced to leave the nest temporarily in order to thermoregulate by cooling off in the water.

## **Behaviour:**

Social behaviour in Nile crocodiles is often underestimated, although there are many aspects still poorly understood.
It has been observed that social status may influence an individual`s feeding success, with less dominant animals tending to eat less in situations where they come into frequent social contact with other, more dominant individuals.

## **Where Crocodiles Are Found:**

Crocodiles are found in south Africa, Botswana, Egypt, Ethiopia, Ivory Coast, Kenya, Madagascar, Mozambique, Namibia, Somalia, Swaziland, Zambia, Zimbabwe.

## **Latin Name:**

*Crocodylus niloticus*.
Given the wide distribution range, a number of population differences have been observed, and several subspecies proposed.

These are rarely differentiated in the literature, however, and they are not officially recognised.

C.

N. africanus (east African Nile crocodile), C.

N.

Chamses (west African Nile crocodile), C.

N.

Corviei (south African Nile crocodile), C.

N.

Madagascariensis (Malagasy Nile crocodile, Malagasy alligator, Croco Mada), C.

N.

Niloticus (Ethiopian Nile crocodile), C.

N.

Pauciscutatus (Kenyan Nile crocodile, Kenya alligator, Kenya caiman), C.

N.

Suchus (Central African Nile crocodile).

#### **Crocodile Bites Hardest:**

Crocodiles may not win the ***'sexiest on the planet'*** category on everyone`s list, but they will be hard to beat when it comes to bite-force champions of the all times.

Crocodiles can kill with the strongest bite force measured for any living animal.

Even their ancestors are keeping the imposing tyrannosaurus rex mum - this according to researchers who found that the bite forces of the largest extinct crocodilians exceeded 10432kg, a force two-times greater than the famous dinosaur.

The researchers from the United States and Australia studied the bite force of all 23 living crocodilian species.

Dr Gignac, instructor of research, department of anatomical sciences, stony brook university school of medicine, and his colleagues from California as well as the Charles Darwin university in Australia roped 83 adult alligators and crocodiles and placed a force metre between their back teeth and recorded the bite force.

They found that gators and crocs have pound-for-pound comparable maximal bite forces, despite different snouts and teeth.

Contrary to previous evolutionary thinking, they determined that bite force was correlated with body size but showed surprisingly little correlation with tooth form, diet, jaw shape, or jaw strength.

Led by project director Gregory Erickson, Ph.

D., professor of biological science at Florida state university, the study took more than a decade to complete and required a diverse team of croc handlers and scientists.

The study is reported online in PLos One.

Among living crocodilians, the bite-force champion is a 5,8 metre saltwater croc.

*"This kind of bite is like being pinned beneath the entire roster of the New York Knicks,"* says Dr Gignac, illustrating the tremendous force displayed by the living creatures.

*"But with bone-crushing teeth."*

The research was funded by the National Geographic Society and the Florida State University College of Arts and Sciences.

**Scientists Prove That Crocodile Hatchling Calls Are Significant:**

For the first time, researchers have shown that the pre-hatching calls of baby Nile crocodiles actually mean something to their siblings and to their mothers.

The calls, which are perfectly audible to humans and sound like ***"umph! umph! umph!"***- tell the others in the nest that it`s time to hatch, according to the report in the June 23 issue of current biology.

Those cries also tell the mother croc to start digging up the nest.

The new findings, made from a series of ***"playback"*** experiments, confirm what had only been suspected on the basis of prior anecdotal observation, according to the researchers Amélie Vergne and Nicolas Mathevon of Université Jean Monnet in France.

The researchers said that the calling behaviour is probably critical to the early survival of the young crocodiles.

Although it has not yet been clearly shown, *"we can well suppose that hatching synchrony can be of vital importance for crocodiles,"*

Mathevon said.

*"Indeed, most mortality occurs early in life and hatching vocalisations might well attract predators.*

*Therefore, adult presence at the nest and its response to juvenile vocalisations may offer protection against potential predators.*

*In this sense, it is important for all embryos in the nest to be ready for hatching at the same time so that they all receive adult care and protection."*

Crocodilians were known to make sounds within the egg shortly before hatching, the researchers said.

To find out what those calls might mean in the new study, the researchers divided crocodile eggs that were due to hatch within 10 days into three groups.

One of those groups was played recordings of pre-hatching calls, one was played recordings of noise, and the last was left in silence until they hatched.

The researchers report that the eggs played the pre-hatch sounds more often answered back.

Many of the eggs in that group also moved.

Finally, all of the eggs in the prehatch group hatched during the playback or within 10 minutes of it.

Only once did the eggs hearing noise hatch, and the rest hatched at least five hours after the last test.

The researchers then tested the mother`s responses to the calls.

*"In the zoo where we did the experiments, eggs are removed [from the nest] within a few days following the laying date,"* the researchers explained.

*"In spite of this, females continue to guard the nest."*

At the end of the incubation period, the researchers hid a loudspeaker underground near the empty nest.

They then played pre-hatching calls interspersed with noise to 10 mothers.

The adults more often turned their heads or moved after egg sounds than after noise, they showed, and eight of the mothers responded to the recorded calls by digging.

The behaviour may have a long history, the researchers said.

*"As birds also produce embryonic vocalisations that induce parental care, such acoustic communication at an early stage of development may be a shared behavioural feature of past and present Archosaurs,"* an ancient group of reptiles now represented by modern birds and crocodiles.

**Gallery:**

Shem Compion.