I’m sitting at a waterhole watching the waterbirds wade along the waters edge as the swallows zig-zag low above the water swooping up unsuspecting insects. What seemed like a peaceful scene suddenly became a frantic flash of silver as small fish broke through the waters surface jumping out of the water in an attempt to escape. Trailing the stream of rising fish we caught a glimpse of a long serrated scaly tail which had broken the surface too. Hunting below the murky water is an ancient species that has survived many thousands of years (as old as the dinosaurs some say). Dominating the niche as the apex predator of any large water bodies throughout the warmer regions of southern Africa is the Nile Crocodile.
Crocodiles are the epitome of stealth, gliding seamlessly through freshwater systems without creating a ripple, but what makes them so successful?
Their ability to move around without being noticed is a major contributing factor to their stealthy ways of sneaking up on unsuspecting prey. Locomotion in crocodiles is done in one of two ways. Firstly, when on land they stand high on all four legs, and with a side-to-side arching of the body, they are then able to walk. However, when they are moving through the water their legs are folded back along the sides of their body and propel themselves forward by means of lateral wavelike motions of the tail. The end of the tail acts as a propeller with the help of its stiffened fin-like scales, reaching speeds of up to 20mph.
Buoyancy is a vital component to the success of crocodiles, almost more so than their ability to move,. This is accomplished by controlling the position of their lungs. Taking a breath allows them to submerge themselves. The crocodiles then use four major muscles to shift the lungs. If they are pulled towards the tail, the centre of buoyancy is further back and this helps the crocodile to dive when propelling forward with its tail. If the crocodile wants to surface the lungs are pulled forward. If the crocodile desires to roll the lungs are pushed to the side.
Crocodiles have enormous, sharp, conical teeth which are powered by a powerful jaw generating incredible forces that are capable of latching on to even the strongest of prey without letting go. Mostly powered by the muscles of the lower jaw, crocodiles are able to generate explosive bite forces reaching as much as 4000 psi (pounds per square inch), the strongest in the animal kingdom and roughly five times stronger than the bite of a lion.
Stealth is required to get close enough to the prey without being noticed, this requires laying motionless in the water and preparing to launch at the prey. The attack is carried out with a combination of propulsion from the tail and the use of the legs to run up the bank, followed by lashing out at the prey with the mouth flared open hoping to catch hold of any body part. Once they have got hold of the prey they don’t intend on using their mouth to kill it, the strategy is to drag it down underwater and drown the prey. Their strong jaw and thick conical teeth are designed to endure stress from all angles as the prey struggles to get free (in turn this is how the crocodile rips pieces of flesh off to feed).
In order to prevent themselves from drowning while wrestling their prey under the water, crocodiles have a valve-like trap door at the back of their throats, preventing water from entering the larynx and the lungs. With this flap closed they are still able to breathe through their nasal passage by laying with their nostrils just breaching the surface of the water. This can be seen below as this crocodile keeps its nostrils above the water while hunting for fish.
Often when driving across the causeway across the Sand River we see crocodiles practising this exact tactic – waiting on the downstream side with the hopes of fish being washed over. With mouths wide open, beady eyes glaring up and with their nictitating membranes closed over, the crocodiles wait in the anticipation of any movement before snapping their mouth shut. They can sit there for hours able to breathe due to this flap. Their eyes and nostrils are positioned on the top of their head, keeping a low profile as they stalk their prey right within inches of the drinking wildebeest on the edge of a waterhole.
This apex predator has adapted to survive with very little changes over thousands and thousands of years, all with many contributing factors that have allowed it to occupy this niche. next time you are crossing the river at the Causeway remember to have a look for this ancient species.