Alligator mississippiensis

American alligators are blackish or olive drab on top. The young have bold yellowish crossbands that may persist inconspicuously into adulthood. The broadly rounded snout lacks conspicuous upward-protruding teeth. Maximum total length is about 19 feet (5.8 meters), but alligators today are generally 13 feet (4 meters) or less (Conant and Collins 1991; see also Ross and Ernst 1994). Males grow much larger than do females. In Florida during 1977-1993, the longest measured male and female alligators were 4.3 m and 3.1 m, respectively (Woodward et al. 1995, J. Herpetol. 29:507-513). Total length is about 8-9 inches (21-23 cm) at hatching. See Allsteadt and Land (1995, Herpetologica 51:314-325) for information on sexual dimorphism in the genital region of young alligators.

This species differs from the American crocodile in having a broader snout and in not having the 4th lower jaw tooth protruding conspicuously upward near the end of the snout (tooth may be inconspicuous in small crocodiles). It differs from the spectacled caiman in lacking a curved, bony, crosswise ridge in front of the eyes.

American alligators inhabit fresh and brackish marshes, ponds, lakes, rivers, swamps, bayous, canals, and large spring runs. They often bask on partially submerged logs or on land next to the water. Alligators dig dens in river or lake margins or in marshes; they spend cold winter and drought periods in the den They depend on access to air holes to survive in ice-covered ponds (Brandt and Mazotti 1990).

Copulation occurs in shallow water. Females deposit eggs in large mounded nests made of leaves, mud, rotting vegetation, rocks, or other debris. Nests are built in marshes or at lake or river margins. In north-central Florida, alligators nested in close proximity to permanent water, used a wide variety of available plant materials and soil in constructing nest (Goodwin and Marion 1978). Turtles (e.g., Pseudemys nelsoni) often lay eggs in alligator nests.

During periods of drought, "gator holes" (deep areas wallowed out by alligators) are important to the survival of individuals of many aquatic animal species.

In Louisiana (Joanen and McNease 1970, 1972), nesting females had a minimum home range of 6.4-41.0 acres; males had minimum home range sizes of 452-12,560 acres and sometimes traveled over 8 km in a day.

Also in Louisiana, annual home range size of 15 radiotracked adult females was 6-166 ha; 12 of the 15 had home ranges under 50 ha (Rootes and Chabreck 1993).

See Brandt (1991) for information on the population biology of an increasing population in South Carolina.

In Georgia, nests incurred a high rate of predation by black bears (Hunt and Ogden 1991).

Spring courtship involves loud bellowing and slapping of the head against the water surface. Reproductive females deposit clutches of usually about 20-60 eggs in May, June, or July (peak in late June-early July in the Everglades, north-central Florida, and Georgia). Eggs hatch in about 9 weeks. Female stays near the nest and may protect it during incubation, and she assists the emergence of the young by opening the nest mound; sometimes she carries the young in her mouth to water. Hatchlings may stay together in the vicinity of the nest and mother for 1-3 years (Behler and King 1979, USFWS 1980). Sexually mature in about 6-7 years.

In most areas, about 25-30% of the adult females nest in a particular year (Rootes and Chabreck 1993); a nesting rate of up to 68% was recorded in one area in southwestern Louisiana (see Taylor et al. 1991).

Reproductive success in the Everglades was constrained primarily by egg mortality caused by flooding (Kushlan and Jacobsen 1990). In north-central Florida, 31% of nests with complete clutches were destroyed by mammalian predators (Goodwin and Marion 1978).