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Swimming
General Biology / Moving around: Crocodiles need to move around in order to survive.

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GENERAL BIOLOGY Locomotion - Swimming
swimming
Swimming alligator (left), underwater freshie (below)
C. johnstoni underwater
TYPE:Behaviour
FUNCTION:Moving the crocodile around in water, for a variety of reasons (e.g. hunting, thermoregulation, social interactions, relocation). Speeds vary from slow drifting to fast, powered swimming over 10kph.
INVOLVING:Tail for propulsion, front and rear legs for steering and movement at very slow speeds

GENERAL | BELLY CRAWL | HIGH WALK | GALLOP | SWIMMING | JUMPING

Usually, very little is said about the most important method of crocodilian locomotion - swimming. While crocodiles are not particularly agile on land, moving only when necessary in most instances, they are far more at home in water - often moving about almost continually for one reason or another. Swimming for a crocodile appears to be almost effortless, and they are capable of great agility and speed in the aquatic medium.

floating caiman

This spectacled caiman (Caiman crocodilus) is demonstrating the classic crocodilian pose as it floats at the water's surface. Its head is above the water, enabling it to see, smell and hear, but its body is underwater and hence far less visible to potential prey. The feet are splayed out to act as stabilisers, the webbing on the rear right foot clearly visible as the caiman pushes down slightly to adjust its position.
It is often said that crocodiles use only their tails for swimming. This is mostly true, but the limbs play an important role, particularly at slow speeds. A crocodile's position in the water depends on its weight and the amount of air in its lungs. In order to float at the surface, the crocodile stores a certain amount of air in its lungs to offset its weight and prevent it from sinking. In this position, the classic crocodilian pose with the head at the surface and the body angled downwards a few inches below the surface, the front and back legs splay out to act as stabilisers and prevent rolling. Minute adjustments are made all the time, and the tail can be used gently to maintain position in flowing water if necessary. Webbing between the toes of the back feet provides surface area which is used to push against the water to help maintain position, and even to move slowly.


hatchling floating at surface This hatchling Australian freshwater crocodile (C. johnstoni) is demonstrating the way it uses its limbs in the water to help keep it afloat. The limbs (both front and hind) are splayed out to each side, partially above the water meniscus. Like the fins of a fish, they prevent the animal from rolling uncontrollably in the water, and also help to stop it from sinking - although the air in the crocodile's lungs is primarily responsible for that.


diving saltwater crocodile If the crocodile wishes to dive, it simply exhales air from its lungs and drops under the surface, the speed of descent depending on the amount of air exhaled. It is thought that stones swallowed and present in the crocodile's stomach (known as "gastroliths") help to add weight and act as a ballast. This helps the crocodile to sink when it exhales sufficient air from its lungs. The added weight further down the body may also act as a counterweight while the head remains close to the surface. The saltwater crocodile to the right is sinking - notice the nictitating membrane which has covered the eye. The milky appearance is typical.


freshie walking on bottom

At the bottom of the pool or river, the crocodile usually walks around without swimming - using its buoyancy to bound effortlessly over aquatic plants and submerged rocks (see C. johnstoni above). When it wants to move through the water more rapidly, however, a crocodile will swim.

webbed A. mississippiensis foot
Webbing is present between the toes of the back feet. This makes the feet more effective as rudders and paddles at slow speed. Webbing between the front feet varies between species, but in most it is reduced or absent.
gharial tail
Undoubtedly, it is the tail (right) which provides virtually all of the thrust for swimming. It is laterally flattened, which means that it has a relatively large surface area to push against the water as it moves from side to side in a sinusoidal (s-shaped) pattern. At slow speeds, the body trunk itself hardly moves - it is only the tail which provides propulsion. The legs can be used for steering, pushing one way or another to help guide the body. As the crocodile speeds up, however, the legs become ineffective in this role and are simply folded back against the body to reduce drag.freshie walking on bottom
The crocodile can use its tail to accelerate very quickly when required, and during enthusiastic swimming the body trunk itself also undulates sinusoidally. For steering, the crocodile usually just points its head in the direction that it wants to go. It can splay its legs out to assist direction changes, but these are usually achieved by using the body and tail to push against the water and provide force to change direction, much as a fish or a sea snake would. In the water, C. porosus are estimated to swim at speeds of up to 10 kph, but a few instances of crocodiles exceeding this have been noted - over 15kph in one instance, and perhaps faster for short bursts. While this might not seem particularly fast compared with, say, galloping, it can be sustained for a much longer period as it requires far less energy expenditure by the crocodile. Unlike galloping, such bursts of speed are often used to catch swimming prey or chase rivals and threats out of territories. Few large animals, especially those more accustomed to movement on land, can escape from a crocodile swimming at full speed.



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