Mike's Wildlife Articles of the Osa
Courtesy of  El Sol de Osa The Osa Peninsula's Newspaper

Osa Safari: The American Crocodile,
by Mike Boston of Osa Aventura

The American Crocodile (Crocodylus acutus) is one of four species of crocodile found in the New World Tropics (Neotropics). It is the most widespread of the New World species, ranging from the tip of Florida through southern Mexico and Central America to Venezuela, Colombia and Ecuador. It is also found throughout many of the West Indian islands.

The other three species have very restricted distributions: the Orinoco crocodile to the Orinoco river basin; Morlete’s crocodile to southeastern Mexico and Belize; and the Cuban crocodile to western Cuba. The latter two species are relatively small crocodiles, seldom exceeding 3 meters in length. However, the American Crocodile, and its sibling, the Orinoco Crocodile, are reputed to reach lengths in excess of 6 meters—and well over one ton in weight! They share the dubious distinction, therefore, of being the largest predators in the Neotropics – a title the American Crocodile alone holds in Central America! However, not that long ago geologically speaking, Porosaurus reigned supreme as one of the largest non-marine predators of all time. This monster crocodile, reaching 16 meters (50 feet) and weighing over 18 tons, terrorized the Amazon Basin up until about 6 million years ago. Its fossilized skull alone weighed 500 kilograms!

This photo shows a common caiman (bottom left) american crocodile (bottom right) and missippi alligator (top). An excellent photo to illustrate the differences between crocs and alligators

Like all crocodilians worldwide (with the possible exception of the Common Caiman), the American Crocodile is threatened with extinction. And like all of its relatives, it has been hunted mercilessly for its skin. In an attempt to rescue this specie from possible extinction, the Convention on International Trade in Endangered Species (CITES) placed the American Crocodile on Appendix 1 (Endangered) in the 1970s, preventing further trade in hides and live specimens among signatory nations. However, thanks to Costa Rica’s rigorous conservation laws and its present system of protected wetlands, this country has ensured a secure future for this majestic crocodilian within its borders. Costa Rica is perhaps the only country in its range where the American Crocodile is still relatively abundant. On both versants of the country sizeable specimens of the American Crocodile can be seen frequently in swamps, tidal estuaries and sluggish rivers. I, personally, have seen American Crocodiles of over 4.5 meters on the upper Río Sierpe, and have been assured by several Park Rangers that 5 to 6 meter specimens live in and around the Corcovado Lagoon in the heart of Corcovado National Park!

The American Crocodile shares its amphibious world in this country with the Common Caiman (Caiman crocodilus). The two species are often confused with one another. However, both represent distinct lineages within the crocodilian reptiles: the American Crocodile is a true crocodile (family Crocodilidae), whose members are pan-tropical; the Common Caiman is in fact an alligator (family Alligatoridae) whose members are confined to the New World (with the curious exception of the Chinese Alligator). The best known member of this group is the Mississippi Alligator from the Southeastern United States. The Common Caiman seldom exceeds 2 meters in length, but the following characters can readily tell specimens of similar size of both species apart:

• The common caiman is dark brown in color with distinct black bands on its tail; the American Crocodile, on the other hand, is drab olive green, and the black markings on its tail do not form bands.
  
• When basking on a riverbank, a Common Caiman will generally hold its head up; the American Crocodile will rest its head on the ground.
  
• The snout of the Caiman is shorter and more rounded, with its eyes and nose more prominently raised; the American Crocodile has a longer, narrower snout, with less prominently raised eyes and nose.
  
• From a dorsal view, the snout of the Caiman is not constricted behind the nose; that of the American Crocodile is distinctly constricted
  

A baby crocodile

When its mouth is shut, only the teeth of the upper jaw of the Common Caiman are visible; the teeth of the lower jaw slot into the upper jaw. In the American Crocodile, however, the teeth of both the lower and upper jaws are both visible

When its jaws are shut – look for the large fourth tooth of the lower jaw which slots into the constriction of the upper jaw behind the nose.

Another difference between the American Crocodile and the Common Caiman is in their habitat preference. Although they cohabit many fresh water areas, the latter is in ways more adaptable and will even inhabit watery ditches, transient pools, and fast flowing creeks. The Common Caiman will rarely, if ever, stray into brackish river estuaries, and never into the sea. The American Crocodile is choosier in its freshwater habitats, favoring lakes, lagoons and sluggish rivers. However, it shares with the Indo-Pacific Crocodile the unique ability to utilize salt-water habitats, such as tidal estuaries, mangroves and the sea. I have often seen American Crocodiles in the seas around the Osa Peninsula, even feeding at sea in front of the Río Sirena, in Corcovado.

We all regard crocodilians as primitive beasts and, let’s face it, their appearance serves only to reinforce this view. But, behind that primordial guise lies a sophisticated animal indeed. We traditionally refer to them as reptiles, with all the lowliness that this grouping implies. But current taxonomic wisdom has elevated the crocodilians to a loftier status and grouped them along with the birds. They share many features and behaviors in common, among them a four-chambered heart (mammals too have four-chambered hearts, but of a different configuration to that of birds and crocodiles) and a sophisticated system of parental care. Snakes, lizards and turtles have two-chambered hearts and rarely engage in any form of parental care. And crocodilians have larger brains than their former reptilian group-mates.

The American Crocodile, like other crocodiles and alligators, guards its eggs throughout the 90-day incubation period from nest robbers such as raccoons, coatimundis, and ocelots. It buries its clutch of about 30 eggs in sandy riverbanks – a characteristic shared with other true crocodiles; alligators bury their eggs in mounds of vegetation. Favorite nesting sites (for example the sandy banks around the Río Corcovado) may be crowded with the nests of many female American Crocodiles. Alerted to the guttural grunts of their hatching young, the female will help unearth them, grasp each of them gently in her powerful jaws and carry her hatchlings to a secluded watery hideaway. The female American Crocodile will then remain in protective care of her young for many months untilthe last one has dispersed.

American Crocodiles of over 3 meters are potentially dangerous to man. Although they don’t have the fearsome reputation of the Indo-Pacific Crocodile of Asia and Australia, or the Nile Crocodile of Africa, nevertheless there have been several cases where American Crocodiles have attacked and killed people in Costa Rica. However, despite their lethal capability, large American Crocodiles are for the most part surprisingly timid beasts. Unless one is foolhardy enough to swim in water that large crocodiles are known to inhabit or to venture too close to a female protecting her nest or young, one need fear little from the American Crocodile.

Crocodilians and their ancestors lived on Earth for over 200 million years and have survived two mass extinctions: 1) the first at the end of the Permian Period, which wiped out 95% of all species, and 2) the second at the end of the Cretaceous, which put pay to the dinosaurs. Let us hope the American Crocodile and its relatives, in all their primeval splendor, can survive this, the next possible mass extinction, into which the natural world of this planet has now entered.

Mike Boston is a biologist, wilderness expedition guide, and the president of Osa Aventura. You can contact him at at info@osaaventura.com