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American Alligator

Description

American AlligatorThe name "alligator" comes from the Spanish "el lagarto," meaning lizard. English speakers, through mispronunciation, first converted the term to "aligarto" and later to "alligator." The American alligator is black in color with rows of rough scales, or scutes, along its back. The reptile’s belly is creamy white, and its eyes are light brown. It can be differentiated from the American crocodile by its large, broad snout. Unlike adults, young alligators have several yellow and white bands along their bodies. Alligators that shared the earth with dinosaurs 180 million years ago looked almost the same and played similar ecological functions as their present-day relatives. The largest alligator on record measured 5.8 meters (19 feet 2 inches) and the heaviest, taken in recent times near Gainesville, Florida, weighed 473 kilograms (1,043 lbs). However, such large and heavy animals are quite uncommon.

Habitat and Biology

Along the Atlantic coast, American alligators are distributed from the Florida Everglades to North Carolina. They also inhabit wetland areas in Texas, Oklahoma, and Arkansas. In South Carolina, American alligators make extensive use of the state’s coastal marshlands, with the ACE Basin being one of the most important nesting areas. High quality alligator habitat found on the coast was created as a result of wetland alteration during the rice-growing era. Rice was introduced to Charleston, South Carolina, around 1680, resulting in the clearing of forested, tidal swamps. Ditch and dike construction permanently altered natural drainage patterns and caused extensive change in wetland plant communities. After the rice industry's demise in the early 1900s, abandoned, diked fields began to deteriorate; however, some dikes and water-control structures were repaired and maintained by sportsmen as waterfowl hunting areas. Today, these impoundments support the highest alligator population and nest densities found in the ACE Basin and the state. Alligator populations gradually decline inland because habitats are seasonally flooded and prey density is reduced.

American alligators are cold-blooded animals, but generally are active year round in South Carolina. Breeding season for the American alligator varies throughout its range because the onset coincides with warmer weather. Nest site selection, construction, maintenance, and protection are important activities in the life of a female alligator. In South Carolina, the majority of nest construction and egg laying takes place during the month of June.

Nests are located on high ground, 1 to 5 meters (3 to 18 ft) from the water’s edge, and consist of a large mound of mud and crushed vegetation. In the ACE Basin, most alligator nests are found in managed impoundments and, to a lesser extent, in remnant impoundments and unaltered marshes. Most nests within impoundments are located on remnant dikes. Nest material is from surrounding vegetation, which is typically giant cordgrass (Spartina cynosuroides) and nests are about 1.5-1.8 m (5-6 feet) in diameter and average 0.5 m (20 in) in height.

Once the mound is complete, the female digs a conical chamber in the center of the mound and deposits 40-45 eggs into the chamber. Several layers of mud and vegetation are then added and compacted atop the egg chamber. Inside it, the eggs are kept at a constant temperature as a result of heat produced by decomposition of the nesting material. Sex of alligators is determined by nest temperatures during the middle third of embryo development. Females are produced at temperatures less than 31.5oC; mixed sex ratios occur at 32oC, and males only are produced when temperatures are between 32.5 and 33oC. Decreasing numbers of males are produced as temperatures approach 35oC, a temperature beyond which only females are produced. Incubation periods average between 63 and 65 days, but can be as long as 77 days. Hatching success averages approximately 70% in South Carolina. Hatchling alligators average about 24 cm (10 in) in total length and weigh 45-55 g (1.5-2.0 ounces). After hatching, juvenile alligators remain together in a group called a pod or creche, which may remain together for up to three years.

Both sexes grow to about 122 cm (4 ft) by age 5. After this age, female growth begins to slow, presumably channeling energy towards reproduction, while males continue to grow fairly rapidly. By age 25, males on average measure 316 cm (10 ft 4 in) and females average 253 cm (8 ft 3 in). Males can reach lengths greater than 394 cm (13 ft) while females rarely exceed 290 cm (9 ft 6 in). Males and females become sexually active when approximately 2.1-2.7 meters (7-9 ft) in length.

Alligator food habits vary by size class, with prey size increasing as alligators get larger. Hatchlings initially depend upon a yolk reserve but will begin feeding almost immediately on invertebrates such as insects, crustaceans, and snails and on small fish. As they grow, larger foods such as snakes, larger insects and frogs become common. Adults feed on aquatic organisms and animals that come to the water’s edge to drink. In estuarine habits, the most common adult food item is blue crabs (Callinectes sapidus). Alligators are also known to feed on dead animals or carrion. Once alligators reach adulthood, they are top-level carnivores and have no natural predators. Raccoons (Procyon lotor), wading birds, and deer (Odocoileus virginianus) are prey items of the largest animals.

Species Significance

In South Carolina, the harvest of American alligators for both food and leather remained unregulated until the 1950s. In 1955, alligators benefited from a law, originally intended to protect deer, that banned night shooting. By the early 1960s, in an effort to reduce poaching, alligator trappers were required by law to possess a license and tags. However, numbers of American alligators in South Carolina continued to decline, resulting in the closure of the season in 1964. Poaching continued even after inclusion of the species in the Endangered Species Protection Act of 1966 and the Endangered Species Conservation Act of 1969. Finally, in 1970, American alligators were included under the Lacey Act of 1900, which prohibited the transport of illegally collected mammals and birds across state boundaries. Throughout the 1970s and 1980s, alligators continued to be protected under the Endangered Species Act of 1973 and were listed as endangered in coastal areas of South Carolina and threatened elsewhere in the state. In 1987, the U. S. Fish and Wildlife Service changed its status to one of "threatened upon similarity of appearance." This was necessary because, even though the species was no longer endangered at that time, such a status would indirectly provide protection to the American crocodile. In 1988, the S.C. Department of Natural Resources implemented a Nuisance Alligator Program. This program was established in an effort to alleviate increasing human-alligator encounters due to rapid urban development in coastal areas. After 31 years of closure, the alligator hunting season in South Carolina was re-opened in 1995. A permit, issued by the S. C. Department of Natural Resources and valid for one year, is required for the marketing and possession of any alligator product.

References

Bara, M. O. 1976. American alligator investigations. Final Study Report. South Carolina Wildlife and Marine Resources Department, Columbia, S.C.

Conant, R. 1975. A field guide to reptiles and amphibians of eastern and central North America. Houghton Mifflin Company, Boston, MA.

Elsey, R. 1998. Personal communication. Louisiana Dept of Wildlife and Fisheries, Rockefeller Refuge, Grand Chenier, LA.

Ferguson, M.J.W. and T. Joanen. 1983. Temperature dependent sex determination in Alligator mississippiensis. Journal Zoological Society of London 200:143-177.

Ferguson, M.J.W and T. Joanen. 1982. Temperature of egg incubation determines sex in (Alligator mississippiensis). Nature 296:850-853.

Grenard, S. 1991. Handbook of Alligators and Crocodiles. Krieger Publishing Co., Malabar, Florida.

Lang, J. W. and H. V. Andrews. 1994 Temperature-dependent sex determination in crocodilians. Journal of Experimental Zoology 270:28-44.

Murphy, T. M. and J. W. Coker. 1984. American alligator population studies in South Carolina. Study Completion Report. South Carolina Wildlife and Marine Resources Department, Columbia, S.C.

Murphy, S. H. and G. Barnette (eds). not dated. South Carolina’s endangered species portfolio - American Alligator. South Carolina Department of Natural Resources, Wildlife Diversity Section, Columbia, SC.

Rhodes, W. E. and J. W. Lang. 1995. Sex ratios of naturally-incubated alligator hatchlings: field techniques and initial results. Proceeding of the Annual Conference of the Southeastern Association of Fish and Wildlife Agencies 49:640-646.

Rhodes, W. 1996. South Carolina Alligator Program 1996 Annual Report. South Carolina Department of Natural Resources, Division of Wildlife and Freshwater Fisheries, Wildlife Management Section.

Strange, T.H. 1987. Goals and objectives of water level manipulations in impounded wetlands in South Carolina. pgs 130-137. In: W.R. Whitman and W.H. Meridith, eds. Waterfowl and wetlands symposium: proceedings of a symposium on waterfowl and wetlands management in the coastal zone of the Atlantic Flyway. Delaware Department of Natural Resources and Environmental Control, Dover, DE.

Wilkinson, P. M. 1983. Nesting ecology of the American alligator in coastal South Carolina. Study Completion Report. South Carolina Wildlife and Marine Resources Department, Columbia, S.C.

Wilkinson, P. M. and W. E. Rhodes. 1992. Nesting habitat of American alligators in coastal South Carolina. Proceeding of the Annual Conference of the Southeastern Association of Fish and Wildlife Agencies 46:260-265.

Wilkinson, P. M. and W. E. Rhodes. 1997. Growth rates of American alligators in coastal South Carolina. Journal of Wildlife Management 61:397-402.



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