American crocodile
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American Crocodile
Crocodylus acutus
Description
The Crocodylus acutus (American crocodile) is a large, greenish-gray crocodilian with black mottling. In Florida, adults reach lengths of about 12 ft (3.8 m) although a specimen measuring 15 ft (4.7 m) was reported in the late 1800s. In other portions of their range, individual crocodiles may reach 20 ft (6.0 m). Like all other crocodilians, males are larger than females. All adults have a hump above the eyes which may or may not be distinct, and irregular, asymmetrical dorsal armoring. Hatchlings measure approximately 10 in (27 cm) and are normally yellowish tan to gray with dark cross markings on the body and tail. These markings fade as the animal grows. A lateral indentation of the upper jaw leaves the fourth tooth of the lower jaw exposed when the mouth is closed. Compared to the alligator, the American crocodile may be distinguished by its longer, narrower, more tapered snout and the exposed fourth tooth of the lower jaw.
Behavior
Females reach sexual maturity at about 7 ft (2.25 m), a size reached at an age of about 10-13 years. It is not known at what age and size males mature. Similarly, the maximum reproductive age for either sex is not known, although it is known that captively reared crocodilians eventually fail to reproduce.
As with most crocodilians, courtship and mating are stimulated by increasing ambient water and air temperatures. Reproductive behaviors peak when body temperatures reach levels necessary to sustain hormonal activity and gametogenesis. In South Florida, temperatures sufficient to allow initiation of courtship behavior are reached by late February through March. Like all other crocodilians, the mating system of the American crocodile is polygynous; each breeding male mates with a number of females. Males typically establish and defend a breeding territory from late February through March. Vocalizations, body posturing, and outright aggression are used to maintain and defend territories and to secure mating privileges with females that roam freely between territories. Male and female American crocodiles go through a ritualistic mating sequence prior to copulation. Courtship in this species is considered to be one of the most structured of all crocodilians, with copulation predictably following precopulatory behaviors.
Following courtship and mating, females search for and eventually select a nest site in which they deposit an average of about 38 elongated oval eggs. Reported clutch size ranges from 8-56 eggs. Although American crocodile nesting is generally considered a non-social event, communal nesting is the norm in parts of the Caribbean, southeast Cuba, and Haiti. In the U. S. several incidents of two clutch nests have been reported. Nest sites are typically selected where a sandy substrate exists above the normal high water level. Nesting sites include areas of well drained sands, marl, peat, and rocky spoil and may include areas such as sand/shell beaches, stream banks, and canal spoil banks that are adjacent to relatively deep water. In some instances, where sand or river banks are not available for nesting sites, a hole will be dug in a pile of vegetation or marl the female has gathered. The use of mounds or holes for nesting is independent of the substrate type and may vary between years by the same female.
The success of American crocodile nesting in South Florida is dependent primarily on the maintenance of suitable egg cavity moisture throughout incubation, nest predation, and flooding. On Key Largo, and other island nests, failure of crocodile nests is typically attributed to dessication due to low rainfall. On Key Largo, about 52% of nests were successful in hatching at least one young. Nest failures on the mainland may be associated with flooding, desiccation, or predation. On the mainland, about 13% of nests monitored were affected by flooding or desiccation, while 13% of nests were partially or entirely depredated. In 1994, surveys found that predation rates on the mainland increased to 27%, while only nine percent of nests failed because of infertility or embryonic mortality. Incubation of the clutch takes about 86 days, during which time the female periodically visits the nest. Some females may also attend and defend their nest throughout incubation, but this behavior is highly variable among individuals and nest defense has not been observed in the U. S. or Cuba. In Florida, American crocodiles are not known to regularly defend their nest against humans. However, all females must return to the nest to excavate hatchlings since the young are unable to liberate themselves from the nest cavity. Parental care after hatching has not been reported for this species in Florida, even though this behavior has been documented in other American crocodile populations.
The young may remain together loosely for several days to several months following hatching, but they are rarely seen with adults. Hatchling survival appears to be low in Everglades National Park (NP) ( 5%), higher at Turkey Point (8.5%), and even higher in the more sheltered habitats of North Key Largo (20.4%). Higher survival on Key Largo has been attributed to the close proximity of nest sites to suitable nursery habitat. On the mainland, nest sites on exposed beaches are often far from nursery habitat, requiring recently hatched young to disperse long distances in unsheltered water. When available, hatchlings seek shelter during the day in beach wrack or among mangrove roots. Predation during these dispersals is probably high, although little information is available to support this conclusion.
The American crocodile is typically active from shortly before sunset to shortly after sunrise. During these times, crocodiles forage opportunistically, eating whatever animals they can catch. Juveniles typically eat fish, crabs, snakes, and other small invertebrates, while adults are known to eat fish, crabs, snakes, turtles, birds, and small mammals. American crocodiles probably feed only rarely during periods of low ambient air temperatures since metabolic and digestive systems are slowed at lower body temperatures.
American crocodiles live sympatrically with American alligators where salinities are low. Most crocodilians tolerate others of the same species and of different ages provided food and other essential habitat requirements are not limiting. Where two or more species coexist, tolerance among species is also common and is usually ensured by species specific differences in habitat utilization. In Florida, the American crocodile and alligator have probably coexisted for thousands of years and relied on changing salinity gradients of surface waters to dictate which species is dominant in certain areas. Though these species probably intermingle frequently throughout the year, there is only one known location where both species may nest side-by-side. If substantiated, the nesting sites along a canal berm in the vicinity of Marco Island, Collier County, would indicate use of a common nesting area by these species. However, the species' breeding seasons may be sufficiently asynchronous in this area to allow crocodiles to breed and nest before alligators become reproductively active.
The depredation rate of American crocodile nests by raccoons in South Florida is low compared to depredation rates other crocodilians suffer from terrestrial nest predators. Therefore, although the raccoon may locally be an important predator, their overall effect on the crocodile population is not considered limiting. Once hatched, crocodilians may be eaten by several species of wading birds and gulls, blue crabs, sharks, and other crocodiles. Though limited, survival information from Key Largo suggests that predation does not limit recruitment of juveniles in that area.
Habitat
The American crocodile is found primarily in mangrove swamps and along low energy man-grove-lined bays, creeks, and inland swamps. In Florida, patterns of crocodile habitat use shifts seasonally. During the breeding and nesting seasons, adults outside of Key Largo use the exposed shoreline of Florida Bay. Males tend to stay more inland than the females at this time, whereas during the non-nesting season, they are found primarily in the fresh and brackish-water inland swamps, creeks, and bays; retreating further into the back country in fall and winter. Along northeastern Florida Bay, crocodiles were found in inland ponds and creeks, protected coves, exposed shorelines and a small number were observed on mud flats. The high use of inland waters suggests crocodiles prefer less saline waters, using sheltered areas such as under-cut banks and mangrove snags and roots that are protected from wind and wave action. Access to deep water greater than 3 ft (1 m) is also an important component of preferred habitats.
Natural nesting habitat includes sites with sandy shorelines or raised marl creek banks adjacent to deep water. Crocodiles also nest on elevated man-made structures such as canal berms and other places where fill has been introduced. In natural nesting situations, creek bank nests are generally considered optimal since these sites provide a good incubation medium and are generally protected from wind and wave action. These nest sites also provide deep water refuge for adult females. Nests adjacent to open water provide little protection from wave action for the nest, hatchlings, or adults. Shore nests are typically not located near good nursery habitat, and mortality of hatchlings is generally higher than in inland nests. Both nesting sites are desirable as there are tradeoffs associated with each and hatching success at each type of location will vary between years depending on climatic conditions.
Distribution
The historic distribution of American crocodiles in southern Florida has been debated for many years, but the overall range of American crocodiles probably has not changed substantially over the past 200 years. Historically, American crocodiles occurred at least as far north on the Florida east coast as Lake Worth, Palm Beach County, to Tampa Bay on the west coast, and as far south as Key West. The distribution of crocodiles during the non-nesting season may vary considerably among years since adult crocodiles can disperse great distances. However, the majority of crocodiles are present in the vicinity of core nesting areas, located near Biscayne and Florida bays.
The current distribution of the American crocodile is limited to extreme South Florida, including coastal areas of Dade, Monroe, Collier, and Lee Counties. Occasional sightings are still reported farther north on the east coast, and a few isolated crocodiles still survive in remnant mangrove habitats in Broward County. Along Florida's southwest coast, several small groups and individual crocodiles have been documented from Sanibel Island, Lee County, south to Collier Seminole State Park, Collier County. Very few reliable reports are available for the Ten Thousand Islands area. Crocodiles are regularly seen in Everglades NP along the mainland shoreline of Florida Bay from the Cape Sable peninsula east to U. S. Highway 1. The species also occurs in Cuba, Hispaniola, Jamaica, Trinidad, and Margarita; and the Atlantic Coast of Mexico from the Bay of Campeche south through the offshore islands of Belize to Venezuela and Colombia. On the Pacific Coast it is found from Sinaloa, Mexico, and the Tres Marias Islands south to coastal Ecuador and the Rio Chira in Peru. Throughout their range, American crocodiles are sympatric with other crocodilians, although they tend to inhabit more saline waters than most other species. In Cuba they overlap with the Cuban crocodile (Crocodylus rhombifer) and in Central America and southern Mexico with the common caiman (Caiman crocodylus) and Morelet's crocodile (Crocodylus moreletti). The American crocodile and alligator are sympatric in brackish-water portions of their range in South Florida, but, due to evolutionary divergence, no hybridization would be expected.
Crocodiles were listed as endangered throughout their range in 1975 and critical habitat was established for this species in 1979. Population declines are most likely associated with habitat alterations and direct human disturbances to crocodiles and their nests.
Historic estimates of the American crocodile population in South Florida are difficult to substantiate because many records are anecdotal and early observations may have been confused with sympatric alligators. In addition, estuarine habitats, preferred by crocodiles, were remote and inaccessible to early settlers, thereby precluding reliable and consistent observations. Between 1,000-2,000 American crocodiles were estimated to exist in South Florida in the early 20th century, but this probably underestimated the population because extensive settlement and associated hunting had already occurred by this time. During the late nineteenth century and the first half of the twentieth century, many of Florida's crocodiles were collected for museums and live exhibits. The species was also legally hunted for its hide and flesh in Florida until about 1962. By the mid 1970s, crocodile numbers had been reduced to between 100-400 non-hatchling individuals. Combined, many of the natural and anthropogenic factors have resulted in adverse effects to the American crocodile. Compared to the historical estimates of 1,000-2,000 animals, populations have declined, and shifts in the nesting distribution have likely occurred. The lowest estimated population levels apparently occurred sometime during the 1960s or 1970s, when the Florida population of the American crocodile was estimated to be between 100-400 non-hatchlings. Kushlan and Mazzotti (1989) estimated that 220-278 adult and subadult crocodiles remained in South Florida, while others believe 500-1,000 individuals persist there currently.
The American crocodile population in south Florida has increased substantially since the 1970s, while still remaining well below historic numbers. The recent increase is best represented by changes in nesting effort. Survey data gathered with consistent effort indicate that nesting has increased from about 20 nests in the late 1970's to about 48 nests in 1995. Since female crocodiles produce only one clutch per year, it follows that the population of reproductively active females has more than doubled in the last 20 years. In addition, since at least a portion of the population's sex ratio approaches 1:1, it is likely that the male portion of the population has also increased substantially.
Threats
In addition to the taking of individual crocodiles, habitat modification and destruction has been occurring since the human settlement of south Florida. Formerly occupied habitats from Lake Worth, Palm Beach County, south to central Biscayne Bay, Dade County, have been largely destroyed by urbanization, and crocodiles have been essentially extirpated from these areas. Similarly, urbanization of the middle and lower Florida Keys has led to habitat degradation and loss. Though crocodiles were never abundant in these areas, further habitat loss limits opportunities for dispersing crocodiles to persist in the middle and lower Keys. Crocodiles were also probably never common along Florida's west coast. Urbanization there has also substantially altered much of the habitat once occupied.
Human encroachment into estuarine habitats can disturb crocodiles to such an extent that normal behavior patterns are altered. As recreational demands increase on public lands, indirect disturbance by apparently innocuous human activities such as camping, fishing, and boating are expected to increasingly affect crocodiles. Observations suggest that repeated close human presence may cause female crocodiles to abandon nests or relocate nest sites. Recreational boating including use of jet skis, has been limited in portions of the American crocodile's habitat within Everglades NP, but public demands for additional recreational opportunities will likely threaten these sanctuaries in the future.
Crocodiles are frequently killed on U. S. Highway 1, and Card Sound Road. On average, three to four crocodiles are killed annually while crossing these roads. Unfortunately, subadults and adults make up the majority of road mortalities. Efforts to preclude crocodile movement across portions of Card Sound Road by fencing sections of the road have been largely unsuccessful, due primarily to improper installation of the fence.
Natural, catastrophic, stochastic events such as hurricanes also are known to adversely affect American crocodiles and may be one of the most important factors limiting the number and distribution of this species in South Florida. Crocodiles are long lived and suffer high juvenile mortality and must, therefore, produce many young over their lifetime to ensure sufficient recruitment and population persistence. Natural events that add substantial adult mortality can result in long periods of little or no recruitment. Failure to successfully recruit age classes in consecutive years can, if repeated periodically, depress small populations.
Crocodiles undoubtedly perish during tropical storms and hurricanes that make landfall in extreme south Florida. The tidal surges, rough seas, and high winds probably result in direct mortality, but may also erode important nesting beaches, destroy nests, and alter other important habitat features. The adverse effects of tropical weather have not been quantified or reported extensively in the literature. Some suggest that the occurrence of major hurricanes at regular intervals may be a factor that serves to hold the Florida crocodile population at some depressed level. Even though extreme south Florida is considered sub-tropical, it is occasionally exposed to sub-freezing temperatures. The effect of freezing temperatures on American crocodile populations is not well known, principally because crocodiles which may be killed during freezes are rarely found. Critical minimum water temperatures are not known, but water temperatures of 55-57°F (13-14°C) in sheltered canals did not result in crocodile mortality during an extremely hard freeze in southern Florida during 1989. Unconfirmed reports identified four dead crocodiles in exposed areas after this freeze but noted that mortality was likely much higher since dead crocodiles were difficult to find. A substantial decline in nesting effort was documented during the following spring, and suggests that adult mortality during the freeze may have been responsible for the observed decline in nesting.
Water salinity affects habitat use and may be locally important especially during periods of low rainfall. Although American crocodiles have salt glands that excrete excess salt and physiological mechanisms to reduce water loss, maintenance of an osmotic balance requires access to low salinity water for juveniles. Hatchling crocodiles are particularly susceptible to osmoregulatory stress and may need to have brackish to fresh water available every four to five days. Crocodiles more than 7 oz (200 g) have sufficient mass to withstand osmoregulatory stress and are not typically believed to be affected by drought. Freshwater needs of the crocodile are usually met with frequent rainfall which results in a layer of fresh water on the surface that may persist for several days after rainfall. Hatchling crocodiles are probably stressed and occasionally die during periods of low rainfall. Anthropogenic changes in the amount and timing of freshwater flow to south Florida may have resulted in shifts in the distribution of American crocodiles. Unfortunately, detailed data on crocodile distribution is only available since the early 1970s and any changes that may have occurred due to hydrological perturbations over the past century cannot be identified with available information.
Conservations And Recovery
Protection of the American crocodile outside of the United States was enhanced when most countries throughout the range of the species became signatories to the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). CITES signatories agreed that, as an Appendix I species, the American crocodile would be afforded protection from international commerce. This protective measure has greatly reduced, and in some cases eliminated illegal harvests of the crocodile for its hide. Other protective measures include prohibitions against hunting all crocodilians in Mexico, and establishment of no-hunting areas in certain portions of Cuba. In 1984 the U.S. Fish and Wildlife Service prepared a recovery plan for the American crocodile. Numerous conservation measures were identified in the recovery plan that were needed to ensure persistence and recovery of the crocodile in south Florida, including securing habitat for all life stages and establishment of self-sustaining populations at natural carrying capacity in appropriate habitats. In addition, the recovery plan for the American crocodile called for research to determine habitat needs, habitat distribution, ownership, and habitat availability to crocodiles. Management options include control of human-related mortality, educating the public, reducing natural mortality, and protecting nest sites.
Recovery efforts for the American crocodile are underway and are likely responsible for increases in the number of crocodiles in South Florida. About 6,500 acres (2640 hectares) have been acquired for protection of crocodiles and other imperiled species at Crocodile Lake National Wildlife Refuge (NWR). Six hundred fifty acres (262 hectares) of this area are wetlands and open water habitats that directly support crocodile conservation. Crocodile habitat is also protected in Everglades NP and Key Biscayne NP, J. N. Ding Darling NWR, Collier Seminole SP, and Key Largo Hammocks State Botanical Preserve. The only habitat extensively used by crocodiles that is not under public ownership is the habitat created by construction of Florida Power and Light's Turkey Point electrical generating facility.
Crocodile nesting continues to be monitored by the Game and Fish Commission, Florida Power and Light, and National Park Service. In 1984, crocodile crossing signs were erected along U. S. Highway 1 to provide public awareness and reduce automobile/crocodile collisions. During future road widening of U. S. Highway 1, box culverts will replace existing small diameter culverts to allow crocodiles to pass under the highway. Fencing also may be erected along portions of U. S. Highway 1 to discourage crocodile movement over the road.
The timing and frequency of the freshwater hydroperiod substantially influences the health of the estuarine environment in south Florida and may be one of the most important large scale factors influencing crocodile populations on the mainland. It is well known that historic alterations to the natural flow have directly affected plant and animal communities. Although there is no direct causal relationship between freshwater flow alterations and American crocodile numbers, some of the population decline witnessed through the 1970s probably was attributable to changes in the amount and timing of surface water flow to South Florida. Future changes in hydrology that mimic natural flow conditions are likely to benefit crocodiles in the long-term, but care should be taken to ensure that changes in the delivery of water do not result in catastrophic, short-term, adverse effects. When added to all other natural and anthropogenic sources of mortality, such habitat changes could have substantial impacts on crocodile nesting and hatchling survival. As advances in water management are made in south Florida, research is expected to continue to assess the effects of changes in the amount and timing of water delivery on the American crocodile.
The availability of fresh water is essential to hatchling crocodile survival. Instream freshwater flow and rainfall provide this water to hatchlings emerging from mainland nests, but hatchlings from islands depend solely on rainfall. During periods of low rainfall, island hatchlings do not gain mass and are less likely to survive during winter months. To increase hatchling survival and recruitment, it was suggested that supplemental sources of fresh water be provided during the three to four month period following hatching. Supplemental sources of fresh water may be particularly important since recent efforts to restore functioning mangrove wetlands in Crocodile Lake NWR has increased salinities in an important crocodile nursery area. Restoration of suitable salinities in this area should be considered if future monitoring indicates low hatchling growth and survival.
Encroachment of exotic vegetation has degraded thousands of hectares of wildlife habitat in south Florida. In coastal areas, and on Key Largo, Australian pine, cajeput, and Brazilian pepper aggressively invade levees and berms. Widespread invasion of C. equisetifolia and to a lesser extent M. quinquenervia and S. terebinthifolia was found at crocodile nesting sites on Key Largo. Many of the exotics were removed during habitat restoration efforts in 1994, but vigorous regrowth and reinvasion is inevitable, and periodic efforts to control exotic vegetation will likely be required to maintain suitability of crocodile nesting sites. Invasive exotics are also encroaching on crocodile nest sites at Turkey Point. However, if measures outlined in Florida Power and Light's crocodile management plan are followed, exotic vegetation would be controlled before it threatened crocodile nesting sites. Renewed efforts may be needed to control exotic plants at Turkey Point. Exotic plant control in Everglades NP should continue. Australian pine has been found, and destroyed by Park staff, on nesting beaches and keys. Management programs or land-use restrictions are used on some public lands to protect and conserve natural resources. In Everglades NP, closure of water bodies has reduced boat traffic and minimized human-crocodile encounters. Unfortunately, restrictions on land and water use are now being challenged and increasing demands for recreational opportunities may threaten crocodiles in some areas. Although human exclusion may be the best management technique for protecting crocodiles and their habitat, it is clear that increasing numbers of the general public do not support this management alternative.
Though management of the physical components of crocodile habitat are essential to the continued survival of this species, emphasis must be placed on minimizing the potential for human-crocodile encounters. Human tolerance for and acceptance of increasing crocodile numbers is one of the primary reasons for the increase in population numbers over the last 20 years. However, as the crocodile population continues to increase, we anticipate an increasing number of human-crocodile conflicts. Unfortunately, dredging of shallow waters and creation of exposed shorelines have resulted in artificial habitats that attract crocodiles to areas adjacent to human habitation. Although American crocodiles are generally considered to be non-aggressive, the public's perception of them is that of a large, dangerous carnivore. If crocodile numbers continue to increase, more encounters will result in an increasing intolerance of crocodiles and more demands for action to reduce human-crocodile conflicts.
Part of the reason for increasing conflicts is that humans have altered the landscape for residential, commercial, or recreational purposes without completely rendering this formerly potential crocodile habitat completely unsuitable. The expanding crocodile population has exploited, and will continue to move into, these habitats and occasionally come into conflict with humans. In order to reduce conflict, one or more of the following must occur: crocodiles must stop using artificial habitats, artificial habitats must be removed or made unavailable, disruptive recreational uses must be seasonally excluded from sensitive habitats, or public education must increase human tolerance of crocodiles.
It is unlikely that the expanding crocodile population will cease using artificial habitats. These areas provide important components of crocodile habitat including basking, nesting, nursery, and deep water refuge. We are even less likely to substantially modify human use of already altered land. For example, homeowners are not likely to abandon their houses because crocodiles bask or nest in their yards. Similarly, filling of deep water channels is improbable since these provide water craft access to waterfront home sites. Seasonal restrictions for disruptive recreational uses such as power boating, jet skis, camping, etc. may be appropriate near crocodile nesting locations. In other areas, new or increased recreational access may not be appropriate since recreational use could result in greater human-crocodile conflict. Implementing recreational restrictions will be difficult, as demands for access continue to increase. However, public education can provide the foundation for developing positive, pro-active attitudes about crocodile conservation. Aggressive public education is probably the most effective method available to ensure the continued growth and recovery of south Florida's American crocodile population.
Throughout the remainder of its range, the American crocodile has suffered from threats similar to those that have adversely affected the species in south Florida. Unfortunately, only Costa Rica and Venezuela have adequately protected the American crocodile and its habitat, although Cuba protects a number of areas with large crocodile populations. Other countries have few or no laws to protect them or are unable to enforce conservation laws that do exist. Current threats to the continued survival of the American crocodile outside of the United States include changes in agricultural, ranching, and forestry practices that affect coastal habitats; developing tourism industries that seek to benefit from tropical, beachfront properties; and legal and illegal hunting. As natural habitats are destroyed and replaced with landscapes that benefit humans, American crocodiles will become increasingly susceptible to the public's intolerance of human/crocodile conflicts.
Contacts
U. S. Fish and Wildlife
Service South Florida Ecological Services
1360 U. S. Highway 1, Suite 5
Vero Beach, FL 32960-4725
Telephone: (561) 562-3909
Fax: (561) 562-4288
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/
References
Britton, A. 1999. Crocodylus acutus (Cuvier, 1807). http://www.flmnh.ufl.edu/natsci/herpetology/brittoncrocs/csp_cacu.html.
Kushlan, J. A. and F. Mazotti. 1989. "Historic and present distribution of the American crocodile in Florda." Journal of Herpetology 23: 1-7.
Kushlan, J. A. and F. Mazotti. 1989. "Population biology of the American crocodile." Journal of Herpetology 23 (1): 7-21
Thorbjarnarson, J. 1989. "Ecology of the American crocodile, Crocodylus acutus." In: Crocodiles. Their Ecology, Management and Conservation. A Special Publication of the Crocodile Specialist Group. World Conservation Union (IUCN), Gland, Switzerland.
U. S. Fish and Wildlife Service. 1997. "Crocodile, American (Crocodylus acutus)." http://endangered.fws.gov/i/c0u.html
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The Crocodylus acutus (American crocodile) is a large, greenish-gray crocodilian with black mottling. In Florida, adults reach lengths of about 12 ft (3.8 m) although a specimen measuring 15 ft (4.7 m) was reported in the late 1800s. In other portions of their range, individual crocodiles may reach 20 ft (6.0 m). Like all other crocodilians, males are larger than females. All adults have a hump above the eyes which may or may not be distinct, and irregular, asymmetrical dorsal armoring. Hatchlings measure approximately 10 in (27 cm) and are normally yellowish tan to gray with dark cross markings on the body and tail. These markings fade as the animal grows. A lateral indentation of the upper jaw leaves the fourth tooth of the lower jaw exposed when the mouth is closed. Compared to the alligator, the American crocodile may be distinguished by its longer, narrower, more tapered snout and the exposed fourth tooth of the lower jaw.
Behavior
Females reach sexual maturity at about 7 ft (2.25 m), a size reached at an age of about 10-13 years. It is not known at what age and size males mature. Similarly, the maximum reproductive age for either sex is not known, although it is known that captively reared crocodilians eventually fail to reproduce.
As with most crocodilians, courtship and mating are stimulated by increasing ambient water and air temperatures. Reproductive behaviors peak when body temperatures reach levels necessary to sustain hormonal activity and gametogenesis. In South Florida, temperatures sufficient to allow initiation of courtship behavior are reached by late February through March. Like all other crocodilians, the mating system of the American crocodile is polygynous; each breeding male mates with a number of females. Males typically establish and defend a breeding territory from late February through March. Vocalizations, body posturing, and outright aggression are used to maintain and defend territories and to secure mating privileges with females that roam freely between territories. Male and female American crocodiles go through a ritualistic mating sequence prior to copulation. Courtship in this species is considered to be one of the most structured of all crocodilians, with copulation predictably following precopulatory behaviors.
Following courtship and mating, females search for and eventually select a nest site in which they deposit an average of about 38 elongated oval eggs. Reported clutch size ranges from 8-56 eggs. Although American crocodile nesting is generally considered a non-social event, communal nesting is the norm in parts of the Caribbean, southeast Cuba, and Haiti. In the U. S. several incidents of two clutch nests have been reported. Nest sites are typically selected where a sandy substrate exists above the normal high water level. Nesting sites include areas of well drained sands, marl, peat, and rocky spoil and may include areas such as sand/shell beaches, stream banks, and canal spoil banks that are adjacent to relatively deep water. In some instances, where sand or river banks are not available for nesting sites, a hole will be dug in a pile of vegetation or marl the female has gathered. The use of mounds or holes for nesting is independent of the substrate type and may vary between years by the same female.
The success of American crocodile nesting in South Florida is dependent primarily on the maintenance of suitable egg cavity moisture throughout incubation, nest predation, and flooding. On Key Largo, and other island nests, failure of crocodile nests is typically attributed to dessication due to low rainfall. On Key Largo, about 52% of nests were successful in hatching at least one young. Nest failures on the mainland may be associated with flooding, desiccation, or predation. On the mainland, about 13% of nests monitored were affected by flooding or desiccation, while 13% of nests were partially or entirely depredated. In 1994, surveys found that predation rates on the mainland increased to 27%, while only nine percent of nests failed because of infertility or embryonic mortality. Incubation of the clutch takes about 86 days, during which time the female periodically visits the nest. Some females may also attend and defend their nest throughout incubation, but this behavior is highly variable among individuals and nest defense has not been observed in the U. S. or Cuba. In Florida, American crocodiles are not known to regularly defend their nest against humans. However, all females must return to the nest to excavate hatchlings since the young are unable to liberate themselves from the nest cavity. Parental care after hatching has not been reported for this species in Florida, even though this behavior has been documented in other American crocodile populations.
The young may remain together loosely for several days to several months following hatching, but they are rarely seen with adults. Hatchling survival appears to be low in Everglades National Park (NP) ( 5%), higher at Turkey Point (8.5%), and even higher in the more sheltered habitats of North Key Largo (20.4%). Higher survival on Key Largo has been attributed to the close proximity of nest sites to suitable nursery habitat. On the mainland, nest sites on exposed beaches are often far from nursery habitat, requiring recently hatched young to disperse long distances in unsheltered water. When available, hatchlings seek shelter during the day in beach wrack or among mangrove roots. Predation during these dispersals is probably high, although little information is available to support this conclusion.
The American crocodile is typically active from shortly before sunset to shortly after sunrise. During these times, crocodiles forage opportunistically, eating whatever animals they can catch. Juveniles typically eat fish, crabs, snakes, and other small invertebrates, while adults are known to eat fish, crabs, snakes, turtles, birds, and small mammals. American crocodiles probably feed only rarely during periods of low ambient air temperatures since metabolic and digestive systems are slowed at lower body temperatures.
American crocodiles live sympatrically with American alligators where salinities are low. Most crocodilians tolerate others of the same species and of different ages provided food and other essential habitat requirements are not limiting. Where two or more species coexist, tolerance among species is also common and is usually ensured by species specific differences in habitat utilization. In Florida, the American crocodile and alligator have probably coexisted for thousands of years and relied on changing salinity gradients of surface waters to dictate which species is dominant in certain areas. Though these species probably intermingle frequently throughout the year, there is only one known location where both species may nest side-by-side. If substantiated, the nesting sites along a canal berm in the vicinity of Marco Island, Collier County, would indicate use of a common nesting area by these species. However, the species' breeding seasons may be sufficiently asynchronous in this area to allow crocodiles to breed and nest before alligators become reproductively active.
The depredation rate of American crocodile nests by raccoons in South Florida is low compared to depredation rates other crocodilians suffer from terrestrial nest predators. Therefore, although the raccoon may locally be an important predator, their overall effect on the crocodile population is not considered limiting. Once hatched, crocodilians may be eaten by several species of wading birds and gulls, blue crabs, sharks, and other crocodiles. Though limited, survival information from Key Largo suggests that predation does not limit recruitment of juveniles in that area.
Habitat
The American crocodile is found primarily in mangrove swamps and along low energy man-grove-lined bays, creeks, and inland swamps. In Florida, patterns of crocodile habitat use shifts seasonally. During the breeding and nesting seasons, adults outside of Key Largo use the exposed shoreline of Florida Bay. Males tend to stay more inland than the females at this time, whereas during the non-nesting season, they are found primarily in the fresh and brackish-water inland swamps, creeks, and bays; retreating further into the back country in fall and winter. Along northeastern Florida Bay, crocodiles were found in inland ponds and creeks, protected coves, exposed shorelines and a small number were observed on mud flats. The high use of inland waters suggests crocodiles prefer less saline waters, using sheltered areas such as under-cut banks and mangrove snags and roots that are protected from wind and wave action. Access to deep water greater than 3 ft (1 m) is also an important component of preferred habitats.
Natural nesting habitat includes sites with sandy shorelines or raised marl creek banks adjacent to deep water. Crocodiles also nest on elevated man-made structures such as canal berms and other places where fill has been introduced. In natural nesting situations, creek bank nests are generally considered optimal since these sites provide a good incubation medium and are generally protected from wind and wave action. These nest sites also provide deep water refuge for adult females. Nests adjacent to open water provide little protection from wave action for the nest, hatchlings, or adults. Shore nests are typically not located near good nursery habitat, and mortality of hatchlings is generally higher than in inland nests. Both nesting sites are desirable as there are tradeoffs associated with each and hatching success at each type of location will vary between years depending on climatic conditions.
Distribution
The historic distribution of American crocodiles in southern Florida has been debated for many years, but the overall range of American crocodiles probably has not changed substantially over the past 200 years. Historically, American crocodiles occurred at least as far north on the Florida east coast as Lake Worth, Palm Beach County, to Tampa Bay on the west coast, and as far south as Key West. The distribution of crocodiles during the non-nesting season may vary considerably among years since adult crocodiles can disperse great distances. However, the majority of crocodiles are present in the vicinity of core nesting areas, located near Biscayne and Florida bays.
The current distribution of the American crocodile is limited to extreme South Florida, including coastal areas of Dade, Monroe, Collier, and Lee Counties. Occasional sightings are still reported farther north on the east coast, and a few isolated crocodiles still survive in remnant mangrove habitats in Broward County. Along Florida's southwest coast, several small groups and individual crocodiles have been documented from Sanibel Island, Lee County, south to Collier Seminole State Park, Collier County. Very few reliable reports are available for the Ten Thousand Islands area. Crocodiles are regularly seen in Everglades NP along the mainland shoreline of Florida Bay from the Cape Sable peninsula east to U. S. Highway 1. The species also occurs in Cuba, Hispaniola, Jamaica, Trinidad, and Margarita; and the Atlantic Coast of Mexico from the Bay of Campeche south through the offshore islands of Belize to Venezuela and Colombia. On the Pacific Coast it is found from Sinaloa, Mexico, and the Tres Marias Islands south to coastal Ecuador and the Rio Chira in Peru. Throughout their range, American crocodiles are sympatric with other crocodilians, although they tend to inhabit more saline waters than most other species. In Cuba they overlap with the Cuban crocodile (Crocodylus rhombifer) and in Central America and southern Mexico with the common caiman (Caiman crocodylus) and Morelet's crocodile (Crocodylus moreletti). The American crocodile and alligator are sympatric in brackish-water portions of their range in South Florida, but, due to evolutionary divergence, no hybridization would be expected.
Crocodiles were listed as endangered throughout their range in 1975 and critical habitat was established for this species in 1979. Population declines are most likely associated with habitat alterations and direct human disturbances to crocodiles and their nests.
Historic estimates of the American crocodile population in South Florida are difficult to substantiate because many records are anecdotal and early observations may have been confused with sympatric alligators. In addition, estuarine habitats, preferred by crocodiles, were remote and inaccessible to early settlers, thereby precluding reliable and consistent observations. Between 1,000-2,000 American crocodiles were estimated to exist in South Florida in the early 20th century, but this probably underestimated the population because extensive settlement and associated hunting had already occurred by this time. During the late nineteenth century and the first half of the twentieth century, many of Florida's crocodiles were collected for museums and live exhibits. The species was also legally hunted for its hide and flesh in Florida until about 1962. By the mid 1970s, crocodile numbers had been reduced to between 100-400 non-hatchling individuals. Combined, many of the natural and anthropogenic factors have resulted in adverse effects to the American crocodile. Compared to the historical estimates of 1,000-2,000 animals, populations have declined, and shifts in the nesting distribution have likely occurred. The lowest estimated population levels apparently occurred sometime during the 1960s or 1970s, when the Florida population of the American crocodile was estimated to be between 100-400 non-hatchlings. Kushlan and Mazzotti (1989) estimated that 220-278 adult and subadult crocodiles remained in South Florida, while others believe 500-1,000 individuals persist there currently.
The American crocodile population in south Florida has increased substantially since the 1970s, while still remaining well below historic numbers. The recent increase is best represented by changes in nesting effort. Survey data gathered with consistent effort indicate that nesting has increased from about 20 nests in the late 1970's to about 48 nests in 1995. Since female crocodiles produce only one clutch per year, it follows that the population of reproductively active females has more than doubled in the last 20 years. In addition, since at least a portion of the population's sex ratio approaches 1:1, it is likely that the male portion of the population has also increased substantially.
Threats
In addition to the taking of individual crocodiles, habitat modification and destruction has been occurring since the human settlement of south Florida. Formerly occupied habitats from Lake Worth, Palm Beach County, south to central Biscayne Bay, Dade County, have been largely destroyed by urbanization, and crocodiles have been essentially extirpated from these areas. Similarly, urbanization of the middle and lower Florida Keys has led to habitat degradation and loss. Though crocodiles were never abundant in these areas, further habitat loss limits opportunities for dispersing crocodiles to persist in the middle and lower Keys. Crocodiles were also probably never common along Florida's west coast. Urbanization there has also substantially altered much of the habitat once occupied.
Human encroachment into estuarine habitats can disturb crocodiles to such an extent that normal behavior patterns are altered. As recreational demands increase on public lands, indirect disturbance by apparently innocuous human activities such as camping, fishing, and boating are expected to increasingly affect crocodiles. Observations suggest that repeated close human presence may cause female crocodiles to abandon nests or relocate nest sites. Recreational boating including use of jet skis, has been limited in portions of the American crocodile's habitat within Everglades NP, but public demands for additional recreational opportunities will likely threaten these sanctuaries in the future.
Crocodiles are frequently killed on U. S. Highway 1, and Card Sound Road. On average, three to four crocodiles are killed annually while crossing these roads. Unfortunately, subadults and adults make up the majority of road mortalities. Efforts to preclude crocodile movement across portions of Card Sound Road by fencing sections of the road have been largely unsuccessful, due primarily to improper installation of the fence.
Natural, catastrophic, stochastic events such as hurricanes also are known to adversely affect American crocodiles and may be one of the most important factors limiting the number and distribution of this species in South Florida. Crocodiles are long lived and suffer high juvenile mortality and must, therefore, produce many young over their lifetime to ensure sufficient recruitment and population persistence. Natural events that add substantial adult mortality can result in long periods of little or no recruitment. Failure to successfully recruit age classes in consecutive years can, if repeated periodically, depress small populations.
Crocodiles undoubtedly perish during tropical storms and hurricanes that make landfall in extreme south Florida. The tidal surges, rough seas, and high winds probably result in direct mortality, but may also erode important nesting beaches, destroy nests, and alter other important habitat features. The adverse effects of tropical weather have not been quantified or reported extensively in the literature. Some suggest that the occurrence of major hurricanes at regular intervals may be a factor that serves to hold the Florida crocodile population at some depressed level. Even though extreme south Florida is considered sub-tropical, it is occasionally exposed to sub-freezing temperatures. The effect of freezing temperatures on American crocodile populations is not well known, principally because crocodiles which may be killed during freezes are rarely found. Critical minimum water temperatures are not known, but water temperatures of 55-57°F (13-14°C) in sheltered canals did not result in crocodile mortality during an extremely hard freeze in southern Florida during 1989. Unconfirmed reports identified four dead crocodiles in exposed areas after this freeze but noted that mortality was likely much higher since dead crocodiles were difficult to find. A substantial decline in nesting effort was documented during the following spring, and suggests that adult mortality during the freeze may have been responsible for the observed decline in nesting.
Water salinity affects habitat use and may be locally important especially during periods of low rainfall. Although American crocodiles have salt glands that excrete excess salt and physiological mechanisms to reduce water loss, maintenance of an osmotic balance requires access to low salinity water for juveniles. Hatchling crocodiles are particularly susceptible to osmoregulatory stress and may need to have brackish to fresh water available every four to five days. Crocodiles more than 7 oz (200 g) have sufficient mass to withstand osmoregulatory stress and are not typically believed to be affected by drought. Freshwater needs of the crocodile are usually met with frequent rainfall which results in a layer of fresh water on the surface that may persist for several days after rainfall. Hatchling crocodiles are probably stressed and occasionally die during periods of low rainfall. Anthropogenic changes in the amount and timing of freshwater flow to south Florida may have resulted in shifts in the distribution of American crocodiles. Unfortunately, detailed data on crocodile distribution is only available since the early 1970s and any changes that may have occurred due to hydrological perturbations over the past century cannot be identified with available information.
Conservations And Recovery
Protection of the American crocodile outside of the United States was enhanced when most countries throughout the range of the species became signatories to the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). CITES signatories agreed that, as an Appendix I species, the American crocodile would be afforded protection from international commerce. This protective measure has greatly reduced, and in some cases eliminated illegal harvests of the crocodile for its hide. Other protective measures include prohibitions against hunting all crocodilians in Mexico, and establishment of no-hunting areas in certain portions of Cuba. In 1984 the U.S. Fish and Wildlife Service prepared a recovery plan for the American crocodile. Numerous conservation measures were identified in the recovery plan that were needed to ensure persistence and recovery of the crocodile in south Florida, including securing habitat for all life stages and establishment of self-sustaining populations at natural carrying capacity in appropriate habitats. In addition, the recovery plan for the American crocodile called for research to determine habitat needs, habitat distribution, ownership, and habitat availability to crocodiles. Management options include control of human-related mortality, educating the public, reducing natural mortality, and protecting nest sites.
Recovery efforts for the American crocodile are underway and are likely responsible for increases in the number of crocodiles in South Florida. About 6,500 acres (2640 hectares) have been acquired for protection of crocodiles and other imperiled species at Crocodile Lake National Wildlife Refuge (NWR). Six hundred fifty acres (262 hectares) of this area are wetlands and open water habitats that directly support crocodile conservation. Crocodile habitat is also protected in Everglades NP and Key Biscayne NP, J. N. Ding Darling NWR, Collier Seminole SP, and Key Largo Hammocks State Botanical Preserve. The only habitat extensively used by crocodiles that is not under public ownership is the habitat created by construction of Florida Power and Light's Turkey Point electrical generating facility.
Crocodile nesting continues to be monitored by the Game and Fish Commission, Florida Power and Light, and National Park Service. In 1984, crocodile crossing signs were erected along U. S. Highway 1 to provide public awareness and reduce automobile/crocodile collisions. During future road widening of U. S. Highway 1, box culverts will replace existing small diameter culverts to allow crocodiles to pass under the highway. Fencing also may be erected along portions of U. S. Highway 1 to discourage crocodile movement over the road.
The timing and frequency of the freshwater hydroperiod substantially influences the health of the estuarine environment in south Florida and may be one of the most important large scale factors influencing crocodile populations on the mainland. It is well known that historic alterations to the natural flow have directly affected plant and animal communities. Although there is no direct causal relationship between freshwater flow alterations and American crocodile numbers, some of the population decline witnessed through the 1970s probably was attributable to changes in the amount and timing of surface water flow to South Florida. Future changes in hydrology that mimic natural flow conditions are likely to benefit crocodiles in the long-term, but care should be taken to ensure that changes in the delivery of water do not result in catastrophic, short-term, adverse effects. When added to all other natural and anthropogenic sources of mortality, such habitat changes could have substantial impacts on crocodile nesting and hatchling survival. As advances in water management are made in south Florida, research is expected to continue to assess the effects of changes in the amount and timing of water delivery on the American crocodile.
The availability of fresh water is essential to hatchling crocodile survival. Instream freshwater flow and rainfall provide this water to hatchlings emerging from mainland nests, but hatchlings from islands depend solely on rainfall. During periods of low rainfall, island hatchlings do not gain mass and are less likely to survive during winter months. To increase hatchling survival and recruitment, it was suggested that supplemental sources of fresh water be provided during the three to four month period following hatching. Supplemental sources of fresh water may be particularly important since recent efforts to restore functioning mangrove wetlands in Crocodile Lake NWR has increased salinities in an important crocodile nursery area. Restoration of suitable salinities in this area should be considered if future monitoring indicates low hatchling growth and survival.
Encroachment of exotic vegetation has degraded thousands of hectares of wildlife habitat in south Florida. In coastal areas, and on Key Largo, Australian pine, cajeput, and Brazilian pepper aggressively invade levees and berms. Widespread invasion of C. equisetifolia and to a lesser extent M. quinquenervia and S. terebinthifolia was found at crocodile nesting sites on Key Largo. Many of the exotics were removed during habitat restoration efforts in 1994, but vigorous regrowth and reinvasion is inevitable, and periodic efforts to control exotic vegetation will likely be required to maintain suitability of crocodile nesting sites. Invasive exotics are also encroaching on crocodile nest sites at Turkey Point. However, if measures outlined in Florida Power and Light's crocodile management plan are followed, exotic vegetation would be controlled before it threatened crocodile nesting sites. Renewed efforts may be needed to control exotic plants at Turkey Point. Exotic plant control in Everglades NP should continue. Australian pine has been found, and destroyed by Park staff, on nesting beaches and keys. Management programs or land-use restrictions are used on some public lands to protect and conserve natural resources. In Everglades NP, closure of water bodies has reduced boat traffic and minimized human-crocodile encounters. Unfortunately, restrictions on land and water use are now being challenged and increasing demands for recreational opportunities may threaten crocodiles in some areas. Although human exclusion may be the best management technique for protecting crocodiles and their habitat, it is clear that increasing numbers of the general public do not support this management alternative.
Though management of the physical components of crocodile habitat are essential to the continued survival of this species, emphasis must be placed on minimizing the potential for human-crocodile encounters. Human tolerance for and acceptance of increasing crocodile numbers is one of the primary reasons for the increase in population numbers over the last 20 years. However, as the crocodile population continues to increase, we anticipate an increasing number of human-crocodile conflicts. Unfortunately, dredging of shallow waters and creation of exposed shorelines have resulted in artificial habitats that attract crocodiles to areas adjacent to human habitation. Although American crocodiles are generally considered to be non-aggressive, the public's perception of them is that of a large, dangerous carnivore. If crocodile numbers continue to increase, more encounters will result in an increasing intolerance of crocodiles and more demands for action to reduce human-crocodile conflicts.
Part of the reason for increasing conflicts is that humans have altered the landscape for residential, commercial, or recreational purposes without completely rendering this formerly potential crocodile habitat completely unsuitable. The expanding crocodile population has exploited, and will continue to move into, these habitats and occasionally come into conflict with humans. In order to reduce conflict, one or more of the following must occur: crocodiles must stop using artificial habitats, artificial habitats must be removed or made unavailable, disruptive recreational uses must be seasonally excluded from sensitive habitats, or public education must increase human tolerance of crocodiles.
It is unlikely that the expanding crocodile population will cease using artificial habitats. These areas provide important components of crocodile habitat including basking, nesting, nursery, and deep water refuge. We are even less likely to substantially modify human use of already altered land. For example, homeowners are not likely to abandon their houses because crocodiles bask or nest in their yards. Similarly, filling of deep water channels is improbable since these provide water craft access to waterfront home sites. Seasonal restrictions for disruptive recreational uses such as power boating, jet skis, camping, etc. may be appropriate near crocodile nesting locations. In other areas, new or increased recreational access may not be appropriate since recreational use could result in greater human-crocodile conflict. Implementing recreational restrictions will be difficult, as demands for access continue to increase. However, public education can provide the foundation for developing positive, pro-active attitudes about crocodile conservation. Aggressive public education is probably the most effective method available to ensure the continued growth and recovery of south Florida's American crocodile population.
Throughout the remainder of its range, the American crocodile has suffered from threats similar to those that have adversely affected the species in south Florida. Unfortunately, only Costa Rica and Venezuela have adequately protected the American crocodile and its habitat, although Cuba protects a number of areas with large crocodile populations. Other countries have few or no laws to protect them or are unable to enforce conservation laws that do exist. Current threats to the continued survival of the American crocodile outside of the United States include changes in agricultural, ranching, and forestry practices that affect coastal habitats; developing tourism industries that seek to benefit from tropical, beachfront properties; and legal and illegal hunting. As natural habitats are destroyed and replaced with landscapes that benefit humans, American crocodiles will become increasingly susceptible to the public's intolerance of human/crocodile conflicts.
Contacts
U. S. Fish and Wildlife
Service South Florida Ecological Services
1360 U. S. Highway 1, Suite 5
Vero Beach, FL 32960-4725
Telephone: (561) 562-3909
Fax: (561) 562-4288
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/
References
Britton, A. 1999. Crocodylus acutus (Cuvier, 1807). http://www.flmnh.ufl.edu/natsci/herpetology/brittoncrocs/csp_cacu.html.
Kushlan, J. A. and F. Mazotti. 1989. "Historic and present distribution of the American crocodile in Florda." Journal of Herpetology 23: 1-7.
Kushlan, J. A. and F. Mazotti. 1989. "Population biology of the American crocodile." Journal of Herpetology 23 (1): 7-21
Thorbjarnarson, J. 1989. "Ecology of the American crocodile, Crocodylus acutus." In: Crocodiles. Their Ecology, Management and Conservation. A Special Publication of the Crocodile Specialist Group. World Conservation Union (IUCN), Gland, Switzerland.
U. S. Fish and Wildlife Service. 1997. "Crocodile, American (Crocodylus acutus)." http://endangered.fws.gov/i/c0u.html
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American crocodile
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American crocodile
| American crocodile | |
|---|---|
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| Conservation status | |
Scientific classification  |
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Branch: | Crocodylomorpha |
| Order: | Crocodylia |
| Family: | Crocodylidae |
| Subfamily: | Crocodylinae |
| Genus: | Crocodylus |
| Species: | C. acutus |
| Binomial name | |
| Crocodylus acutus Cuvier, 1807 |
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| 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 within many river systems on Cuba, Jamaica, and Hispaniola. Within the United States, the American crocodile is only found within the southern half of Florida, which has an estimated population of about 2000. The habitat of the American crocodile consists largely of coastal areas. It is larger than some other crocodile species, with some males reaching lengths of 6.1 metres (20 ft) in Central and South America.
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Description
Like all crocodilians, the American crocodile is a quadruped, with four short, splayed legs, a long, powerful tail and a scaly hide with rows of ossified scutes running down its back and tail.[2] 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.[2] Camouflage also helps them prey on food. The snout is relatively longer and narrower than the American alligator, although broader on average than the Orinoco crocodile.[3] 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".[4] Larger specimens can charge up to 10 miles per hour (16 km/h).[5] They can swim at as much as 20 miles per hour (32 km/h) by moving their bodies and tails in a sinuous fashion, but they cannot sustain this speed.[6]
American crocodiles are more susceptible to cold than American alligators.[7] While an American alligator can subsist in water of 7.2 °C (45.0 °F) for some time, an American crocodile in that environment would become helpless and drown.[2] American crocodiles, however, have a faster growth rate than alligators, and are much more tolerant of salt water.[2]
Cleaning symbiosis
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.[2]
Size
Newborn hatchlings are about 22 centimetres (8.7 in) in length and about 60 grams (2 oz) in mass.[8][9] The average adult is 4 metres (13 ft) long and weighs 382 kilograms (840 lb) in males, and 3 metres (9.8 ft) and 173 kilograms (380 lb) in females.[10][11]
In the Tárcoles River in Costa Rica, dozens of four-meter and a few five-meter 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. In their US range, adult length has been recorded as much as 5.2 metres (17 ft), but adult males on average measure only 4 metres (13 ft) long. This species is said to grow largest in the South American river basins, but even old males rarely reach 6 metres (20 ft).[12][13] A skull of this species was found to measure 72.6 centimetres (28.6 in) and is estimated to have belonged to a crocodile of 6.6 metres (22 ft) in length.[14] 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).[15] The longest American crocodile ever actually measured from snout to tail is a 18 feet (5.5 m) male living within the Tarcoles River of Costa Rica. In the spring of 2008, two biologists working with The History Channel's series MonsterQuest (June 17, 2009) spotted and filmed what they estimated to be a 17–19 foot crocodile living deep in the Everglades.
Diet
American crocodiles' primary prey throughout life is fish; the relatively narrow snout is indicative of this piscivorous preference. Virtually any fish found in freshwater through coastal salt water habitats is potential prey. In Florida, bass, tarpon and especially mullet appeared to be the primary prey.[16] Prey species can range in size from the insects taken by young crocodiles to cattle taken by large adults, and can include, beyond fish, birds, mammals, turtles, crabs, snails, frogs, and occasionally carrion.[11][17] Adult American crocodiles have no natural predators. Reportedly, these crocodiles hunt primarily in the first few hours after nightfall, especially on moonless nights, although they will feed at any time.[16]
Breeding
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, so 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 mother may cover the eggs with debris or leave them uncovered. The white, enlongated eggs are about 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 racoons, foxes, skunks or other scavenging mammals. Crocodilian eggs are somewhat brittle, but softer than bird eggs. Young of this species hatch after 75–80 days.
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 instinctually 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 11 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 various raptorial birds and larger fishes. 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.[16]
Range and distribution
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 on the Caribbean Islands,[2] southern Florida, the Greater Antilles and southern Mexico to Colombia and Ecuador.[8][17] The American crocodile is especially plentiful in Costa Rica.[18] One of its largest documented populations is in Lago Enriquillo, a landlocked, hypersaline lake in the Dominican Republic.[11] The species has also been recorded from Jamaica.[19]
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 (only 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 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.[20][21]
American crocodiles in the United States coexist with the American alligator, and are primarily found in Everglades National Park, Florida Bay, Biscayne Bay and the Florida Keys from Miami southward.[7][9] A sizable population occurs near Homestead, Florida, at the Turkey Point Nuclear Generating Station.[9][22][23] Some individuals wander northward to warm summer waters and have been sighted in Sarasota County and Palm Beach County.[8] In the summer of 2008, a crocodile was captured in the surf on Isle of Palms, South Carolina.
They coexist with the very small spectacled caiman within Central America. The only other crocodiles present within the American crocodile's range are the smaller and critically endangered Cuban crocodile, along with the small Morelet's crocodile in southern Mexico and Guatemala.
Systematics
Cuvier originally described the species as Crocodylus acutus in 1807.[24] Over time, it commonly became known as the "sharp-snout alligator". In 1822, Constantine Samuel Rafinesque postulated the species was in fact a crocodile.[25]
The species was redescribed as Crocodylus floridanus by William T. Hornaday in 1875,[26][27] when Hornaday and C.E. Jackson were sent from Washington, D.C. 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!"[28]
Crocodylus floridanus is now considered an invalid junior synonym of C. acutus.[29][30]
The American crocodile is sometimes confused with the smaller, Central American Morelet's crocodile.
Conservation status
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.[9] In 1972, Venezuela banned commercial crocodile skin harvesting for a decade, as a result of 1950s and 1960s overhunting.[31]
One thousand to two thousand American crocodiles live in Mexico and Central and South America, but populations are data deficient.[11] 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.[32] 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.[33][34]
Interaction with humans
See also: Crocodile attacks
American crocodiles can be dangerous to humans, and 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.[2] The species is often reportedly timid, and seemingly lacks the propensity to attack humans as regularly as Old World crocodiles do.[25] However, it is more likely to be aggressive towards humans than the American alligator.[16] 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.[35][36] No attacks on humans by the American crocodile have been reported in the United States, despite assorted anecdotes.[37]
See also
References
- ^ a b c Crocodile Specialist Group (1996). Crocodylus acutus. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 7 December 2008. Listed as Vulnerable (VU A1ac v2.3)
- ^ a b c d e f g Guggisberg, C.A.W. (1972). Crocodiles: Their Natural History, Folklore, and Conservation. Newton Abbot: David & Charles. p. 195. ISBN 0-7153-5272-5.
- ^ [1] (2011).
- ^ Gregg, Gordon; Gans,Carl (PDF). Morphology & Physiology of the Crocodylia. http://eprint.uq.edu.au/archive/00002011/02/croc.pdf.
- ^ "American Crocodile". Rainforest Exploration. Earth's Birthday Project. http://www.earthsbirthday.org/explore/teachers/infocrocodile.htm. Retrieved 2008-12-12.[dead link]
- ^ "American Crocodile". Everglades. Miami Science Museum. http://www.miamisci.org/ecolinks/everglades/crocinfo.html. Retrieved 2008-12-12.
- ^ a b Kushlan, JA; 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.
- ^ a b c Conant, Roger; Collins, Joseph T (1998). Reptiles and Amphibians Eastern-Central North America (3rd ed.). Boston: Houghton Mifflin. pp. 142–3. ISBN 0-395-90452-8.
- ^ a b c d Moller, Michelle P.; Cherkiss, Michael S. Mazzotti, Frank J.. "The American Crocodile: A Story of Recovery". The Croc Docs. Fort Lauderdale Research and Education Center. http://crocdoc.ifas.ufl.edu/publications/posters/crocodilerecovery/. Retrieved 2008-12-12.
- ^ Savage, Jay M.; Fogden, Michael; Fogden, Patricia (2005). The Amphibians and Reptiles of Costa Rica: A Herpetofauna between Two Continents, between Two Seas. University Of Chicago Press. ISBN 978-0-226-73538-2.
- ^ a b c d "American Crocodile". Animals. National Geographic Society. http://animals.nationalgeographic.com/animals/reptiles/american-crocodile.html?nav=A-Z. Retrieved 2008-11-29.
- ^ Behler JL, King FW. 1979. The Audubon Society Field Guide to North American Reptiles and Amphibians. New York: Alfred A. Knopf. 743 pp. LCCCN 79-2217. ISBN 0-394-50824-6.
- ^ USA. "American Crocodiles, American Crocodile Pictures, American Crocodile Facts - National Geographic". Animals.nationalgeographic.com. http://animals.nationalgeographic.com/animals/reptiles/american-crocodile.html. Retrieved 2011-11-15.
- ^ Wood, Gerald (1983). The Guinness Book of Animal Facts and Feats. p. 256. ISBN 978-0-85112-235-9.
- ^ "ANIMAL BYTES - American Crocodile". Seaworld.org. http://www.seaworld.org/Animal-info/animal-bytes/animalia/eumetazoa/coelomates/deuterostomes/chordata/craniata/reptilia/crocodylia/american-crocodile.htm. Retrieved 2011-11-15.
- ^ a b c d [2] (2011).
- ^ a b "American Crocodile (Crocodylus acutus)". Crocodilians: Natural History & Conservation. Florida Museum of Natural History. http://www.flmnh.ufl.edu/cnhc/csp_cacu.htm. Retrieved 2008-11-29.
- ^ "8 Crocodiles kill man in Mexico". Sindh Today. 12 August 2008. Archived from the original on 2008-08-22. http://web.archive.org/web/20080822053412/http://www.sindhtoday.net/world/11409.htm. Retrieved 2008-11-29.
- ^ Ahrenfeldt, Robert H. (1954-05-05). "Identification of the Amphibia and Reptilia Recorded in Jamaica growing rapidly by Hans Sloane (1688-89)". Copeia (American Society of Ichthyologists and Herpetologists) 1954 (2): 105–111. doi:10.2307/1440328. JSTOR 1440328.
- ^ www.crocodilian.com
- ^ Dr. Adam Britton
- ^ "Providing a home for the American crocodile" (PDF). Florida Power & Light. http://www.fpl.com/environment/plant/pdf/turkey_point_crocodile_fact_sheet.pdf.
- ^ Allen, Greg (21 April 2007). "American Crocodiles Make a Comeback". National Public Radio. http://www.npr.org/templates/story/story.php?storyId=9718547. Retrieved 2008-12-12.
- ^ * "Crocodylus acutus". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=174361. Retrieved 24 December 2008.
- ^ a b Levin, Ted (2004). Liquid Land: A Journey Through the Florida Everglades. University of Georgia Press. ISBN 0-8203-2672-0.
- ^ Hornaday, William T.. "The crocodile in Florida". The American Naturalist 9.
- ^ "A New Day Dawns in the Everglades". Audubon Magazine. July–August 2001. http://audubonmagazine.org/features0107/everglades_intro.html. Retrieved 2009-01-08.
- ^ Hornaday, William T. (1925). A Wild-animal Round-up. C. Scribner's Sons. p. 147. http://books.google.com/?id=_00lAAAAMAAJ&q=%22whale+of+a+saurian%22. Retrieved 2008-12-28.
- ^ * "Crocodylus floridanus". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=209643. Retrieved 24 December 2008.
- ^ Stejneger, Leonhard (1933-10-15). "Crocodilian Nomenclature". Copeia (American Society of Ichthyologists and Herpetologists) 1933 (3): 117–120. doi:10.2307/1436233. JSTOR 1436233.
- ^ Pough, F. Harvey; Robin M. Andrews; John E. Cadle; Martha L. Crump; Alan H. Savitsky, Kentwood D. Wells (2004). Herpetology (3rd ed.). Upper Saddle River, New Jersey: Pearson/Prentice Hall. pp. 628–9. ISBN 0-13-100849-8.
- ^ "American Crocodile (Crocodylus acutus)". National Parks Conservation Association. http://www.npca.org/marine_and_coastal/marine_wildlife/crocodile.html. Retrieved 2008-12-07.
- ^ "U.S. Crocodiles Shed "Endangered" Status". National Geographic Society. 21 March 2007. http://news.nationalgeographic.com/news/pf/98669458.html. Retrieved 2008-12-07.
- ^ American Crocodile No Longer Near Extinction. March 21, 2007.
- ^ "Boy killed in crocodile attack in Mexico". msnbc.com. Associated Press. 3 May 2007. http://www.msnbc.msn.com/id/18474361. Retrieved 2008-11-29.
- ^ "Crocodile makes off with boy". Television New Zealand. Reuters. 5 May 2007. http://tvnz.co.nz/view/page/411749/1098603. Retrieved 2008-11-29.
- ^ Langley, Ricky L. (2005). "Alligator Attacks on Humans in the United States" (PDF). Wilderness and Environmental Medicine 16 (3): 119–124. PMID 16209465. http://www.allenpress.com/pdf/weme_16_303_119_124.pdf.
External links
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Wikispecies has information related to: Crocodylus acutus |
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Wikimedia Commons has media related to: Crocodylus acutus |
- American Crocodile
- American Crocodile at Crocodilian Species List
- University of Florida's crocodile research in Southwest Florida
- National Parks Conservation Association - American Crocodile
- American crocodile at the Encyclopedia of Life
Media
- Crocodylus acutus at CalPhotos
- ARKive images and movies of the American crocodile (Crocodylus acutus)
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