Crocodiles and alligators have six modes of locomotion. These are swimming, belly-crawl, high-walk, galloping, floating, and diving. They are well designed for swimming, where their movement appears fluid and effortless. However, on land, these crocodilians appear ponderous and sluggish.
The belly crawl is the most frequently land locomotion employed by crocodiles and alligators. In this mode, its legs are splayed out to the side like a lizard (but the crocodile is not a lizard), and its feet are pointed outwards away from its body when it moves.
There are several variations to the belly crawl. The "true" belly crawl is usually employed at very slow speeds. In it, the crocodile slides along the ground with its smooth-scaled chest, stomach, and tail on the ground. It propels itself forward by diagonally moving its legs. That is, the right front and left rear legs are lifted and moved forward while the front right and rear left legs, already on the ground, push backwards, propelling the crocodile's body forward. Then the process is repeated with the alternate set of legs.
At slow belly crawl speeds, the crocodile's body remains relatively rigid. But as it increases speed, it lifts its body higher to almost clear the ground. Its body undulates from side to side, and its tail also swishes from side to side with each stride. This gait allows the crocodile to exert more force in each step, thereby increasing its speed and ground clearance. Depending on the surface, a crocodile can reach speeds of 5 to 10 kph using this technique. Crocodiles often use the higher speed belly crawl to escape potential threats, usually into a body of water.
When high walking , a crocodile or alligator positions its legs erect beneath its body and lifts its entire body and nearly half its tail off the ground. It can travel at speeds of between 2-4kph in this way, with short bursts of up to 5kph. The crocodile can do this because it can rotate its feet 90 degrees forward rather than facing out sideways, and holding its legs upright and close to its body when it adopts this gait.
Crocodile Running (Galloping)
A crocodile can run at full gallop at a speed of up to 17kph (11mph). An alligator is slightly faster than a crocodile, reaching a maximum speed of approximately 18kph (11 mph). They can maintain these speeds for less than 100 meters before they become exhausted.
Crocodiles and alligators run by lifting the front of their body up and throwing their front limbs out and forward as the hind limbs thrust the body forward. They then land on their front limbs first and repeat the process. This motion is similar to a horse galloping. A running crocodile is a terrifying sight indeed.
A crocodile can swim at speeds of up to 29 kph over short distances. An alligator swims at 32kph (20mph).By comparison, an average human can swim at only 3 kph.
When swimming, the crocodile and alligators place their limbs against their bodies and propel themselves by swinging their flexible, laterally flattened tail from side to side in a wavelike motion.
At slow speeds, only the tail moves, and its limbs are used to steer and stabilise it through the water. But as its speed increases, the crocodile folds its limbs against its body and undulates its body from side to side, magnifying the trust force it exerts on the water. It steers by using its head as a rudder.
A crocodile’s position in water (above the water, below the water, or underwater) depends on the amount of air in its lungs. By varying the volume of air in its lungs, the crocodile can control its buoyancy. For example, if a crocodile wishes to dive, it exhales air from its lungs, causing its body to sink in the water. The classic crocodilian pose in the water is the 'float' which can take two forms; the horizontal or vertical float.
In the horizontal float position, the crocodile stays motionless on the water's surface, with a portion of its upper body floating above the surface of the water. While in this position, the crocodile splays out its legs to act as stabilisers to prevent it from rolling. Slight adjustments are made by using its legs, especially its webbed hind legs. It may also wag its tail gently to maintain its position in flowing water.
In the vertical position, the crocodile will only have its head above the water. It will either stand or float underwater to achieve this position. With its head above the water, it can see, smell and hear what's happening around it while being less visible to its potential prey.
Crocodile Diving & Submersion
When a crocodile or alligator wishes to submerge, it exhales air from its lungs to reduce its buoyancy, moves its limb in an upward motion, and slides underwater, with barely a ripple. Once below the surface, the crocodile swims or walks underwater. The crocodile can hold its breath for as long as one hour.