American crocodile

American crocodile
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Crocodylomorpha
Order: Crocodilia
Family: Crocodylidae
Subfamily: Crocodylinae
Genus: Crocodylus
Species: C. acutus
Binomial name
Crocodylus acutus
Cuvier, 1807
Approximate terrestrial range (green)
Synonyms

The American crocodile (Crocodylus acutus) is a species of crocodilian found in the Neotropics. It is the most widespread of the four extant species of crocodiles from the Americas. Populations occur from the Atlantic and Pacific coasts of southern Mexico to South America as far as Peru and Venezuela. It also lives on many of the Caribbean islands such as Cuba, Jamaica, Hispaniola and Grand Cayman.

Within the United States, the American crocodile's distribution is limited to Puerto Rico and the southern half of Florida, though at least two have been found as far north as the Tampa Bay area.[2] The current US population, estimated at 2,000, represents a significant recovery from a few hundred in the 1970s.

The habitat of the American crocodile consists largely of coastal areas.[3] It is also found in river systems, but has a tendency to prefer, not merely to tolerate, some level of salinity, resulting in the species's congregating in brackish lakes, mangrove swamps, lagoons, cays, and small islands. Other crocodiles also have tolerance to salt water due to salt glands underneath the tongue, but the American crocodile is the only species other than the saltwater crocodile (C. porosus) to commonly live and thrive in salt water.[4] They can be found on beaches and small island formations without any freshwater source, such as some of the many cays and islets across the Bahamas and the Caribbean. They are also found in hypersaline lakes; one of the largest known populations inhabits the Lago Enriquillo.[5]

The American is one of the larger crocodile species. Males can reach lengths of 6.1 m (20 ft), weighing up to 907 kg (2,000 lb).[5] On average, mature males are more in the range of 4.1 m (13 ft) to 4.8 m (16 ft) in length weighing about 400 kg (880 lb).[6] As with other crocodile species, females are smaller; rarely exceeding 3.8 m (12 ft) in length.[7]

This species has a more V-shaped snout, compared to other large crocodiles, which usually have a slightly wider snout. Adults have a uniform grayish-green coloration with white or yellow undersides, while juveniles have dark cross-banding on the tail and back. Despite their large size, American crocodiles do not regularly attack large animals, as most large crocodilians do. Fish, reptiles, birds and small mammals make up the majority of their diet. On occasion, large mammals such as deer and cattle are taken. Their dietary habits in coastal regions are not well studied. Like any other large crocodilian, the American crocodile is potentially dangerous to humans, but it is not a very aggressive species and attacks are rare.[8]

Taxonomy and etymology

Cuvier originally described the species as Crocodylus acutus in 1807.[9] Over time, it commonly became known as the "sharp-snout alligator". In 1822, Constantine Samuel Rafinesque postulated that the species was in fact a crocodile.[10]

The species was redescribed as Crocodylus floridanus by William T. Hornaday in 1875,[11][12] when Hornaday and C.E. Jackson were sent from Washington, DC to Florida to collect alligator hides. Upon hearing of a "big old gator" in Arch Creek at the head of Biscayne Bay, Hornaday and his companions searched for it and reported:

"In a few hours we got sight of him, out on the bank in a saw-grass wallow. He was a monster for size—a perfect whale of a saurian, gray in color—and by all the powers, he was a genuine crocodile!"[13]

Crocodylus floridanus is now considered an invalid junior synonym of C. acutus.[14][15]

Characteristics

Large American crocodile skull
Adult American crocodile

Like all crocodilians, the American crocodile is a quadruped, with four short, stocky legs, a long, powerful tail and a scaly hide with rows of ossified scutes running down its back and tail.[16] Its snout is elongated and includes a strong pair of jaws. Its eyes have nictitating membranes for protection along with lachrymal glands, which produce tears.

The nostrils, eyes, and ears are situated on the top of its head, so the rest of the body can be concealed underwater for surprise attacks.[16] Camouflage also helps it prey on food. The snout is relatively longer and narrower than that of the American alligator (Alligator mississippiensis), although broader on average than that of the Orinoco crocodile (C. intermedius). American crocodiles are also paler and more grayish than the relatively dark-hued alligator. This crocodile species normally crawls on its belly, but it can also "high walk".[17] Larger specimens can charge up to nearly 10 mph (16 km/h).[18] They can swim at as much as 20 mph (32 km/h) by moving their bodies and tails in a sinuous fashion, but they cannot sustain this speed.[19]

American crocodile

The American crocodile is sometimes confused with the smaller, Central American Morelet's crocodile, a smaller species that is native to Mexico.

Size

Newborn hatchlings are about 27 cm (10.6 in) in length and about 60 g (2.1 oz) in mass.[20][21] The average adult in the continental rivers can range from 2.9 to 4 m (9 ft 6 in to 13 ft 1 in) long and weigh up to 382 kg (842 lb) in males, while females can range from 2.5 to 3 m (8 ft 2 in to 9 ft 10 in) and weigh up to 173 kg (381 lb), the lower total length representing their average size at sexual maturity, the upper representing the expected upper size limit for the respective sex in most known populations.[22][23][24]

In the Tárcoles River in Costa Rica, dozens of 4 m (13 ft 1 in) and a few 5 m (16 ft 5 in) individuals frequent bridge crossings (where they are fed daily, which may have helped them reach such consistently large sizes) and are a popular tourist attraction. This species is said to grow largest in the South American river basins, but rarely exceed 5 m (16 ft 5 in) or reach 6 m (19 ft 8 in) even there.[25][26] Crocodiles on the islands or coasts are usually much smaller in size. Adult weight in coastal Belize averaged 77.8 kg (172 lb) per one study.[27] In their Florida range, adult length has been recorded as high as 5.2 m (17 ft 1 in), but adult males on average measure 3.35 m (11 ft 0 in) long, perhaps slightly smaller than mature males from other continental populations.[28][29] A skull of this species was found to measure 72.6 cm (28.6 in) and is estimated to have belonged to a crocodile of 6.6 m (22 ft) in length.[29] Large, mature males regularly weigh about 400–500 kg (880–1100 lb), with the individuals of six or more meters surpassing 1000 kg (2,200 lb).[30] Two biologists working with the History Channel series MonsterQuest spotted and filmed a crocodile they estimated to be 5 to 5.5 m (16 ft 5 in to 18 ft 1 in), deep within Everglades National Park in Florida.

Distribution and habitat

American crocodiles (left) and American alligators (right) are usually tolerant of one another in places where they co-exist, such as this sand pond in Florida. However, they sometimes compete with each other for food and other resources

C. acutus is the most widespread of the four extant species of crocodiles from the Americas.[1] It inhabits waters such as mangrove swamps, river mouths, fresh waters, and salt lakes, and can even be found at sea, hence its wide distribution throughout the Caribbean islands, southern Florida, the Greater Antilles, southern Mexico, Central America, and the South American countries of Colombia and Ecuador.[20][31] The American crocodile is especially plentiful in Costa Rica.[32] One of its largest documented populations is in Lago Enriquillo, a hypersaline lake in the Dominican Republic.[23] The species has also been recorded from Jamaica.[33] American crocodiles have recently been sighted in Grand Cayman, leading experts to believe the species may be swimming from Cuba (which is home to a massive American crocodile population) and slowly repopulating Grand Cayman. In addition, an American crocodile/Cuban crocodile hybrid was recently discovered in the Cancun area. The crocodile likely originated in the Zapata Swamp of Cuba (the only place where these wild hybrids exist) and swam to the Yucatán Peninsula. Their saline tolerance also allowed the American crocodile to colonize limited portions of the United States (Puerto Rico and extreme southern Florida). Contrary to popular misinformation, the presence of the American alligator is not the reason the American crocodile was unable to populate brackish waters north of Florida, but rather the climate.

American crocodile found in Jamaica's Black River

American crocodiles, unlike American alligators, are extremely susceptible to cold temperatures and live exclusively within tropical waters. During 2009, unusually cold weather in southern Florida resulted in the deaths of about 150 wild American crocodiles, including a well-known crocodile which inhabited Sanibel Island far north of their natural range.[34]

Large group of American crocodiles on Cuba

American crocodiles in the United States coexist with the American alligator, and are primarily found south of the latitude of Miami, in Everglades National Park, Florida Bay, Biscayne Bay, and the Florida Keys.[21][35] A sizable population occurs near Homestead, Florida, at the Turkey Point Nuclear Generating Station.[21][36][37] Some individuals wander northward to warm summer waters and have been sighted in Sarasota County and Palm Beach County.[20] In the summer of 2008, a crocodile was captured in the surf on Isle of Palms, South Carolina. In 2013, a 700-pound crocodile was captured in Tarpon Springs, Florida.[38] Florida Fish & Wildlife Conservation Commission program staff note that the crocodile was not weighed to be 700 lbs. The weight was estimated by the Nuisance Alligator Trapper who inadvertently caught the animal using a baited hook. American crocodiles of similar lengths have been accurately weighed at 450–500 lbs.

The American crocodile is saltwater-tolerant and have thus been capable of colonizing a multitude of islands within the Caribbean islands and on some coastal Pacific islands as well. They coexist with the rather smaller spectacled caiman within Central America. The only other crocodiles present within the American crocodile's range are two species smaller than this species on average: the critically endangered Cuban crocodile, along with the Morelet's crocodile in southern Mexico and Guatemala.

Biology and behavior

American crocodiles are more susceptible to cold than American alligators.[35] While an American alligator can survive in water of 7.2 °C (45.0 °F) for some time, an American crocodile in that environment would become helpless and drown.[16] American crocodiles, however, have a faster growth rate than alligators, and are much more tolerant of salt water.[16]

American Crocodile, Costa Rica

Cleaning symbiosis involving the American crocodile as client has been described. Unlike the Old World crocodiles, which are sometimes cleared of parasites by birds, the American crocodile relies more on fish for parasite removal.[16]

Hunting and diet

Adult male C. acutus

American crocodiles are apex predators, and any aquatic or terrestrial animal they encounter in freshwater, riparian and coastal saltwater habitats is potential prey. For a long time, primary prey throughout their lifetime was thought to be fish; due to the relatively narrow snout as indicative of this piscivorous preference. However new studies shed light into the dietary preference of this species. The snout of the American crocodile is broader than some specialized fish-eating crocodilians (i.e. gharials (Gavialis gangeticus), freshwater crocodile (C. johnsoni), etc.), allowing it to supplement its diet with a wider variety of prey. In addition the snout gets even broader and bulkier as the animal matures, a sign for a shift in prey items. Prey species have ranged in size from the insects taken by young crocodiles to full-grown cattle taken by large adults, and can include various birds, mammals, turtles, crabs, snails, frogs, and occasionally carrion.[23][31] In Haiti, hatchling and juvenile crocodiles lived primarily off of fiddler crabs (Uca ssp.), making up 33.8% and 62.3% of the diet by weight, respectively.[39] Elsewhere, aquatic insects and their larvae and snails are near the top of the food list for crocodiles at this very early age. Immature and subadult crocodiles, per a study in Mexico, have a more diverse diet that can include insects, fish, frogs, small turtles, birds and small mammals. One specimen of 1.2 m (3 ft 11 in) had a catfish, a mourning dove (Zenaida macroura) and a bare-tailed woolly opossum (Caluromys philander) in its stomach.[40] In Florida, bass, tarpon (Megalops atlanticus) and especially mullet, large crabs, snakes, mammals that habit the riparian and coastal regions of the Everglades, such as opossums and raccoons appeared to be the primary prey of subadult and adult American crocodiles.[41] In Haiti, adults appeared to live largely off of various birds (many of which are breeding large waders and other water birds such as heron, storks, flamingos (Phoenicopterus ruber), pelicans (Pelecanus ssp.), grebes, coots (Fulica americana) and moorhens (Gallinula chloropus)), followed by concentrations of marine fish including Tilapia and Cichlasoma, at times being seen to capture turtles, dogs and goats.[39] One 3 m (9 ft 10 in) adult from Honduras had stomach contents consisting of a 1.5 m (4 ft 11 in) crocodile of its own species, a turtle shell and peccary hooves.[42] It was noted that historically in Mexico that, among several local farmers, the capturing of livestock by crocodiles has been a source of some conflict between humans and crocodiles and large adults occasionally can become habitual predators of goats, dogs, pigs and cattle.[40] In Quintana Roo, Mexico, most prey that could be determined was fish for sub-adults and adults with sub-adults having a broader prey base than either younger or adult crocodiles.[43] In Costa Rica, American crocodiles have been recorded hunting and killing adult female olive ridley sea turtles (Lepidochelys olivacea) when they come to nest around beaches.[44] Reportedly, these crocodiles hunt primarily in the first few hours after nightfall, especially on moonless nights, although they will feed at any time.[41] It hunts in the typical way for most crocodilian, ambushing terrestrial prey when it comes to edge of the water or is sitting in shallows and dragging it down to be drowned or attempting to ambush aquatic prey from near the surface of the water.[24]

Interspecies predatory relations

Adult American crocodiles have no natural predators and almost any terrestrial or riparian animal they encounter is potential prey. American crocodiles are known predators of lemon sharks, and sharks avoid areas with crocodiles.[45][46] Usually American crocodiles are dominant over alligators. However on one occasion, an American crocodile, in a Florida zoo escaped its cage and started a fight with a large male American alligator in a bordering pen and was killed by the alligator.[29] Conversely, there is one confirmed case of a crocodile preying on a sub-adult alligator in the wild in Florida.[47] Alligators and crocodiles do not often come into conflict in the wild normally, due largely to habitat partitioning and largely separate distributions.[48] There are several records of American crocodiles killing and eating spectacled caimans (Caiman crocodilus) in South America as well as additional records of cannibalism there. Areas with healthy American crocodile populations often hold only limited numbers of spectacled caimans, while conversely areas that formerly held crocodiles but where they are now heavily depleted or are locally extinct show a growth of caiman numbers, due to less competition as well as predation.[47] In areas where the two species coexist, the smaller but more aggressive Cuban crocodile is behaviorally dominant over the larger American crocodile.[49] In Mexico some Morelet's crocodiles individuals have escaped from captivity, establishing feral populations and creating a problem for the populations of American crocodile, which must compete with this invasive species.[50]

Reproduction

American crocodiles breed in late fall or early winter, engaging in drawn-out mating ceremonies in which males emit very low frequency bellows to attract females. Body size is more important than age in determining reproductive capabilities, and females reach sexual maturity at a length of about 2.8 m (9.2 ft). In February or March, gravid females will begin to create nests of sand, mud, and dead vegetation along the water's edge. Nest location is crucial, and with the correct amount of vegetation, the eggs will develop within a small temperature range. Because sex determination is temperature-dependent in crocodilians, slight aberrations in temperature may result in all-male or all-female clutches, which would possibly harm the health of the population. About one month later, when it is time to lay, the female will dig a wide hole diagonally into the side of the nest and lay 30 to 70 eggs in it, depending on her size. After laying, the female may cover the eggs with debris or leave them uncovered. The white, elongated eggs are 8 cm (3.1 in) long and 5 cm (2.0 in) wide and have a number of pores in the brittle shell. During the 75- to 80-day incubation period, the parents will guard the nest, often inhabiting a hole in the bank nearby. Females especially have been known to guard their nests with ferocity. But in spite of these precautions, crocodile eggs sometimes fall prey to raccoons (Procyon sp.) (arguably the most virulent natural predator of crocodilian nests in the Americas), coatis, foxes, skunks or other scavenging mammals (even coyotes (Canis latrans) in Mexico and American black bears (Ursus americanus)) in south Florida), as well as large predatory ants, crabs and vultures.[47] In Panama, green iguana (Iguana iguana) were seen to dig up and prey on American crocodile eggs occasionally, although in several cases were caught by the mother crocodile and subsequently consumed.[51] Crocodilian eggs are somewhat brittle, but softer than bird eggs. Young of this species hatch after 75–80 days.

An American crocodile hatchling in Colombia

This species exists mostly in tropical areas with distinct rainy seasons, and the young hatch near the time of the first rains of the summer (July–August), after the preceding dry season and before the bodies of water where they live flood. In this stage of development of their young, mother crocodiles exhibit a unique mode of parental care. During the hatching process, when the young crocodiles are most vulnerable to predation, they will instinctively call out in soft, grunt-like croaks. These sounds trigger the female to attend to the nest, uncovering the eggs if they have been covered. Then she will aid the hatchlings in escaping their eggs and scoop them up with her mouth, carrying them to the closest water source.

The hatchlings, which are 24 to 27 cm (9.4 to 10.6 in) in length, have been reported to actively hunt prey within a few days of hatching. It is not uncommon for the mother to care for her young even weeks after they have hatched, remaining attentive to their calls and continuing to provide transportation. About five weeks after hatching, the young crocodiles disband in search of their own independent lives. Most of them, of course, will not survive, being preyed upon by several types of raptorial birds and larger fishes (e.g. barred catfish (Pseudoplatystoma fasciatum), Atlantic tarpons (Megalops atlanticus), common snook (Centropomis undecimalis) and lemon sharks (Negaprion brevirostris)), boa constrictors (Boa constrictor), black spiny-tailed iguana (Ctenosaura similis), spectacled caimans, as well as raccoons.[47] Those that do survive the early stages of life will grow rapidly, feeding on insects, fish and frogs. Additionally, some young crocodiles reportedly will feed on each other.[41]

Conservation status

Crocodylus acutus in La Manzanilla, Jalisco, Mexico

Due to hide hunting, pollution, loss of habitat, and removal of adults for commercial farming, the American crocodile is endangered in parts of its range.[21] In 1972, Venezuela banned commercial crocodile skin harvesting for a decade, as a result of 1950s and 1960s overhunting.[52]

1,000–2,000 American crocodiles live in Mexico and Central and South America, but populations are data deficient.[23] The American crocodile is considered a vulnerable species, but has not been assessed since 1996.[1] It has an estimated wild population of 500 to 1,200 in southern Florida.[53] On March 20, 2007, the United States Fish and Wildlife Service declassified the American crocodile as an endangered species, downgrading its status to "threatened"; the reptile remains protected from illegal harassing, poaching, or killing under the federal Endangered Species Act.[54][55] In southern Florida, 67.8% of crocodile mortality was attributed most likely to road collisions (found dead by the road), 10.5% were due to intentional killing and only 4.9% could be contributed to natural causes (the remaining balance were causes unknown).[56]

Relationship with humans

American crocodiles are dangerous to humans; attacks in Mexico, Costa Rica, and Panama are not unprecedented. These attacks rarely make international news, so this species is not as well-documented as a man-eater, as are its relatives.[16] The species is often reportedly timid, and seemingly lacks the propensity to attack people as regularly as Old World crocodiles do.[10] Crocodiles are, as a general rule, more aggressive than alligators. The American crocodile rates, temperamentally somewhere in the middle of all crocodilians .[41] A study by the IUCN found that the American crocodile has the highest incidence of reported attacks on humans, but fatalities were rare <Sideleau & Britton>. The estimated number of attacks is considerably smaller than those by the saltwater and Nile crocodiles (C. niloticus). The saltwater and Nile crocodiles are considered to be the most aggressive and dangerous species towards humans.[57] Reportedly, the Cuban crocodile (C. rhombifer) is rather more aggressive in interspecies interactions than the American crocodile and apparently attacks and displaces American crocodiles when they are kept in mixed species enclosures at zoos or at crocodile farms together, even though it is smaller than the American species. However, attacks are rarely reportedly in Cuban crocodiles, undoubtedly due its much more limited habitat and range.[24][57] In May 2007, two instances occurred within one week of children being attacked and killed by this species—one in Mexico just south of Puerto Vallarta and one in Costa Rica.[58][59] On August 24, 2014, a man and a woman were swimming in a canal in Gables by the Sea, a community in Coral Gables, Florida, at 2:00 AM, in a canal where crocodiles were known to occur, when they were bitten in the shoulder and the hand by an American crocodile. Although the crocodile was 12' 1" in length, and weighed an estimated 550 lbs, it did not press the attack, but released. and moved away from its victims. (Florida Fish & Wildlife Conservation Commission, Crocodile Response Program) This was the first documented wild crocodile attack on humans in Florida since records of human-crocodile conflict have been kept.[60] On May 19, 2015, a seven-year-old boy was attacked and killed by an American Crocodile in the Barra Santa Ana estuary near the city of Lazaro Cardenas, Mexico.[61] This was reportedly the eighth crocodile attack in the Barra Santa Ana estuary in the last two years.[61]

See also

References

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  35. 1 2 Kushlan, J. A.; Mazotti, F. (1989). "Historic and present distribution of the American crocodile in Florida". Journal of Herpetology. 23 (1): 1–7. doi:10.2307/1564309. JSTOR 1564309.
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  39. 1 2 Thorbjarnarson, J. B. (1988). The status and ecology of the American crocodile in Haiti. Bulletin of the Florida State Museum. Biological Sciences (USA).
  40. 1 2 Alvarez del Toro, M. (1974). Los Crocodylia de México (estudio comparativo). Smith III.
  41. 1 2 3 4 "American Crocodile". People.wcsu.edu. Retrieved 2013-04-25.
  42. ↑ Schmidt, K. P. (1924). Notes on Central American crocodiles. Publs. Field Mus. Nat.
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  44. ↑ Ortiz, R. M., Plotkin, P. T., & Owens, D. W. (1997). "Predation upon olive ridley sea turtles (Lepidochelys olivacea) by the American crocodile (Crocodylus acutus) at Playa Nancite, Costa Rica" (PDF). Chelonian Conservation and Biology. 2: 585–586.
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