Feeding ecology and diet

Crocodilians are renowned for their ability to acquire food, often violently. All species are carnivorous, and mostly generalist. A wide range of mammals, birds, reptiles, amphibians, crustaceans, mollusks, fishes, and insects are taken readily by adults of most species. There are various restrictions, however. Young juveniles are limited to small prey that enter or approach water, primarily insects, spiders, crustaceans, fishes, small reptiles, and amphibians. Juveniles eat regularly, each day if possible. As they grow, the size and range of available prey increases. Species with specialized foraging strategies as adults (such as gharials) begin to exhibit characteristic preferences.

Although anything that moves within striking range is often considered fair game for adult crocodilians, most species display some selection criteria. These may include prey avail ability, but also species-specific preferences influenced by morphology and ecology. Broad-snouted alligatorids with strong bites and blunt teeth include hard-shelled prey in their diet; slender-snouted species such as gharials have weaker bites, but their sharp, undifferentiated teeth and slender jaws are ideal for sweeping quickly through water to seize slippery fish. Many Crocodylidae possess jaws between these two extremes, reflecting a generalist diet influenced by prey distribution and seasonal availability. Species with more specialized jaws will, however, take other prey where available.

Crocodilians display several hunting techniques. Surprisingly, most prey are small and taken as they approach the head, even in very large adults. The kill zone is an arc traced by the head and neck, although some species literally dive onto prey just below the surface. Terrestrial prey are ambushed at the water's edge, the hunter is either submerged or exposes only the eyes and nostrils. Once within striking range, there is an explosion of teeth and water as the crocodilian propels itself forward using its tail and limbs. Larger prey are dragged into the water where they drown. Although not pack hunters, the presence of several crocodilians in the water speeds a prey's demise. However, capture is not always successful. Misses are common, and large prey bitten on the head, limbs, or body may escape, only to die later from their injuries.

Although there are stories of crocodiles using their tails to sweep prey off their feet, hard evidence is sorely lacking, though the tail is important in hunting. Larger crocodiles are often seen using the tail to herd small fish into shallow water to be scooped up with a sweep of open jaws. The tail can be used to push the body vertically out of the water, ideal for catching prey flying over the water or hanging in low branches. This behavior has been witnessed in many species. Several species are reported to form a living dam with their bodies, preventing migrating fish from escaping. By cooperating, many individuals increase their chances of success. Nile crocodiles frequently cooperate after large prey is captured, taking turns to hold the carcass while others spins their bodies to rip off mouthfuls of flesh. Crocodilians learn rapidly to associate events with outcomes, often attending predictable events such as prey migrations.

Once captured, small prey is deftly manipulated by the jaws for immediate swallowing; head raised, the prey is flicked into the throat under gravity. Larger prey is first crushed several times by the back teeth, perforating skin and shell to assist digestion. Prey too large to be swallowed is typically held firmly in the jaws, then the head is whipped violently to one side. This tears prey apart, and each piece is swallowed once retrieved. Very large prey is first dismembered by holding onto a piece with the jaws, then spinning the body axis several times to twist it off. The carcass is anchored by its own weight, or by other feeding crocodilians. Live prey are easily incapacitated by rolling, as defense against this maneuver is impossible. Once inside the stomach, food is subjected to highly acidic gastric juices. The action of the muscular stomach plus gastrolith stones slowly macerates flesh and renders bone and shell into smaller pieces. Only keratin (found in hair, nails, and turtle shell) is immune. Compacted balls of indigestible material are regularly coughed up.

Frequently classed as man-eaters, only a handful of species are considered a significant threat to humans. Most fatalities are reported from American alligators, estuarine crocodiles, and Nile crocodiles, the latter responsible for the greatest number of crocodile-related deaths each year with several hundred people estimated killed or seriously injured. Threats can be reduced significantly by educating people to the danger posed by crocodilians, and providing alternative means of accessing water.

Was this article helpful?

0 0

Post a comment