Crocodilian Picnic

This is my first article for children to be published here.

 Can some animals feed together, apparently enjoying the experience the same way we do at picnics?

            This is the feeling we get when we consider cooperative feeding, one of the two amazing bahaviors of crocodilians.  

            Who are crocodilians? 

Crocodilians are large reptiles, averaging 20 ft 5 in (6.2 m) in length. They have a lizardlike shape and a rough, scaly, and waterproof skin. They usually weigh 500 lbs (225 kg) but could go up to 2057 lbs (910 kg). 

Habitat

These reptiles inhabit any wet area in warm regions: lakes, rivers, ponds, freshwater and mangrove swamps, brackish water, waterholes, estuaries, and freshwater marshes. They also travel easily on land.

What do they eat

Usually crocodilians eat fish and smaller vertebrates. However they may also consume large mammals like baboons, hyenas, impalas, young hippopotamuses, buffalo, giraffes, lions, porcupines, zebras, and antelope.

While a crocodilian may eat alone, they sometimes feed together in a cooperative manner.

Cooperative eating  

Cooperative eating occurs when:

1. there is a large number of fish swimming with a current into a body of water;

2. crocodilians line themselves side-by-side across the current;

3. the banding together is so tight that one could walk on their heads or backs;

4. a crocodilian abandons its position, another fills it;

5. there is little or no fighting over prey; and

6. the crocodilians are so engrossed in the feeding that they ignore distractions.  

The first observation of cooperative feeding in crocodilians was made by William Bartram in his Travels in Georgia and Florida, 1773-1774. On the St. Johns River in Florida, not far from Lake Dexter, Bartram noted a large number of alligators lined up close together from shore to shore. Above them a large mass of various kinds of fish waded through the narrow pass of the river into the little lake to spawn. As they came in, they were caught and swallowed by the alligators. The flapping of their tails could be heard about half a mile away.  

Bartram again described cooperative feeding by alligators in the sinkhole at the eastern end of the Alachua Savanna or the Paynes Prairie. "In and about the Great Sink, are incredible numbers of crocodiles [alligators] taking up fish, which continually crowd in upon them from the river and creeks draining from the savanna, especially the great trout [largemouth black bass], mudfish, catfish, and various species of bream."

In 1890 in Buzzard Roost Lake in Okefenokee Swamp, Georgia, Allen Chesser’s witness of cooperative fishing in alligators was reported in Francis Harper’s 1926 Tales of the Ofekinokee thus:. “Hyere the lake an' hyere's a little run [a channel] goes out erbout thirty yards broad. An' right hyere at the en' is a little round lake. The Alligators cared nothin' fer us. There must 'a' ben three hundred uv 'em. They'd ketch fish that long [indicating about a foot and a half]. Ef they'd ketch a perch, yer'd hear 'im flutterin' in their mouth. They wuz that thick, I could 'a' walked down that road on Gator haids."

Pooley and Gans wrote about cooperative feeding in The Nile crocodile (1976): "Cooperation may be seen when rivers rise and the water flows into channels leading to pans (natural depressions), along the river. Crocodiles form a semicircle where a channel enters a pan, facing the inrushing water and snapping up the fish that emerge from the river. Each crocodile stays in place and there is no fighting over prey.”

Pooley, describing Food and feeding habits in Crocodiles and Alligators (1989), gave more details about cooperative feeding in Nile crocodiles: "In Lake St. Lucia, Natal, South Africa, there are annual migrations of shoal fish out of and into the lake from the Indian Ocean. Large numbers of crocodiles move down from northern and open stretches of the lake in response to the fish shoaling;  …

"They congregate in the Narrows, a channel less than 500 meters (550 yards) in width. Cooperative feeding can be observed with several crocodiles spreading out in a semicircular or line formation, which blocks the passage of the fish. Each crocodile maintains its place in line and snaps at approaching fish. There is no fighting over prey; 

"In other Zululand rivers similar behavior may be seen in summer when rivers flood and water spills into channels leading to natural pans. The crocodiles form a barrier where a channel enters the pan, facing the inrushing water and snapping up river fishes such as bream (genus Tilapia) and catfish."  

Schaller and Crawshaw, in Feeding behavior of Paraguayan caiman (1982) found similar behavior in Caiman crocodilus in Brazil: "When heavy rain created a wide riffle between ponds, 7-15 caiman fished in it all day.”  

Thorbjarnarson, in a Ph.D. dissertation (1991), Ecology and behavior of the spectacled caiman in the central Venezuelan Llanos, narrated their cooperative feeding: "In shallow, moving water caiman would orient the body parallel to the flow of water and capture prey by making rapid sideswipes.”

          Cooperative feeding occurs in culverts too, although less intense. This has been explained in Caiman crocodilus gathered at road culverts; in Paynes Prairie State Preserve, where small numbers of American alligators lined up and cooperatively fed in the flow from culverts in north Florida; and also in Everglades National Park in south Florida.   

End

            Although not a common sight, American alligators, Nile crocodiles, and spectacled and Yacare caiman crocodilians do eat together, apparently enjoying the experience the same way we do at picnics.          

      

Sidebar    

                                                                                                             

Why are crocodilians able to live in water?

The eyes, ears, and nostrils of crocodilians are found on the same plane on the top of  the head, allowing them to be completely submerged underwater while still being able to see, hear, and smell. When they dive, the external ears and the nostrils of crocodilians close. They also close their third eyelid, the transparent nictating membrane, to keep water out of their eyes. They have a special throat pouch which enables them to eat underwater. Crocodilians have a flap of skin at the back of their throats which closes off their respiratory system when they are underwater. This allows them to open their mouths underwater without choking.

What are the three families of crocodilians?

There are three families of Crocodylia: Alligatoridae, Crocodylidae, and Gavialidae

How can we distinguish (them) crocodilians from alligators?

Crocodilians can be distinguished from alligators by their long narrow snout and their fourth mandibular tooth, which portrudes from their lower jaw rather than fitting in to their upper jaw. The teeth are long and conical. The teeth on the top jaw are in line with the bottom jaw, a feature which distinguishes all crocodiles from alligators. The fourth lower tooth is larger than the others and can be seen when the mouth is closed.

How strong are the muscles in a crocodilian’s jaw? 

The muscles which draw shut a crocodilian’s mouth are very powerful. Hence they are capable of applying many tons of pressure with their bite. But the muscles that open the crocodile's jaws are very weak. Therefore when a crocodilian clamps its mouth shut, a person can hold it shut without the animal being able to open it.

How is the sight of crocodilians?

The pupils of crocodilians are vertical slits which widen at night, giving them great vision.