Figure 1. The American Alligator Alligator mississippiensis
The American alligator (Alligator mississippiensis, Fig. 1) is the most common of two crocodilians native to the United States and is one of 22 crocodilian species worldwide. The other native crocodilian is the American crocodile (Crocodylus acutus). Caimans (Caiman spp.), imported from Central and South America, are occasionally released in the United States and can survive and reproduce in Florida. The American alligator is distinguished from the American crocodile and caiman by its more rounded snout and black and yellow-white coloration. American crocodiles and caimans are olive-brown in color and have more pointed snouts. American alligators and crocodiles are similar in physical size, whereas caimans are 40% smaller.
General Biology, Reproduction, and Behavior
Alligators are ectothermic — they rely on external sources of heat to maintain body temperature. They are most active at warmer temperatures and prefer 82o to 92o F (28o to 33o C). They stop feeding when ambient temperature drops below 70o F (21o C), and become dormant below 55o F (13o C).
Alligators are among the largest animals in North America. Males can attain a size of more than 14 feet (4.3 m) and 1,000 pounds (473 kg). Females can exceed 10 feet (3.1 m) and 250 pounds (116 kg). Alligators of both sexes become sexually mature when they attain a length of 6 to 7 feet (1.8 to
2.1 m), but their full reproductive capacity is not realized until females and males are at least 7 feet (2.1 m) and 8 feet (2.4 m) long, respectively.
Alligators begin courtship in April throughout most of their range, and breed in late May and early June. Females lay a single clutch of 30 to 50 eggs in a mound of vegetation from early June to mid-July. Nests average about 2 feet (0.6 m) in height and 5 feet (1.5 m) in diameter. Nests are constructed of the predominant surrounding vegetation, which is commonly cordgrass (Spartina spp.), sawgrass (Cladium jamaicense), cattail (Typha spp.), giant reed (Phragmytes spp.), other marsh grasses, peat, pine needles, and/or soil. Females tend their nests and sometimes defend them against intruders, including humans. Eggs normally take 65 days to complete incubation. In late August to early September, 9- to 10-inch (23- to 25-cm) hatchlings are liberated from the nest by the female. She may defend her hatchlings against intruders and stay with them for up to 1 year, but gradually loses her affinity for them as the next breeding season approaches.
Growth rates of alligators are variable and dependent on diet, temperature, and sex. Alligators take 7 to 10 years to reach 6 feet (1.8 m) in Louisiana, 9 to 14 years in Florida, and up to 16 years in North Carolina. When maintained on farms under ideal temperature and nutrition, alligators can reach a length of 6 feet (1.8 m) in 3 years.
Alligators are not normally aggressive toward humans, but aberrant behavior occasionally occurs. Alligators can and will attack humans and cause serious injury or death. Most attacks are characterized by a single bite and release with resulting puncture wounds. Single bites are usually made by smaller alligators (less than 8 feet [2.4 m]) and result in an immediate release, possibly because they were unsure of their intended prey. One-third of the attacks, however, involve repeated bites, major injury, and sometimes death. Serious and repeated attacks are normally made by alligators greater than 8 feet in length, and are most likely the result of chase and feeding behavior. Unprovoked attacks by alligators smaller than 5 feet (1.5 m) in length are rare.
Contrary to popular belief, few attacks can be attributed to wounded or territorial alligators, or females defending their nests or young. Necropsies of alligators that have attacked humans have shown that most are healthy and well-nourished. It is unlikely that alligator attacks are related to territorial defense. When defending a territory, alligators display, vocalize, and normally approach on the surface of the water where they can be more intimidating. In most serious alligator attacks, victims were unaware of the alligator prior to the attack. Female alligators frequently defend their nest and young, but there have been no confirmed reports of humans being bitten by protective females. Brooding females typically try to intimidate intruders by displaying and hissing before attacking.
Alligators quickly become conditioned to humans, especially when food is involved. Food-habituated alligators lose their fear of humans, and can be dangerous to unsuspecting people, especially children. Many aggressive or “fearless” alligators have to be removed each year following feeding by humans. Ponds and waterways at golf courses, and high-density housing, create a similar problem when alligators become accustomed to living near people.
The American alligator is found in wetlands throughout the coastal plain of the southeastern United States. Viable alligator populations are found in Texas, Oklahoma, Arkansas, Louisiana, Mississippi, Alabama, Florida, Georgia, South Carolina, and North Carolina. The northern range is limited by low winter temperatures. Alligators are rarely found south of the Rio Grande drainage. Alligators prefer freshwater, but also inhabit brackish water and occasionally venture into salt water. American crocodiles are scarce, and in the United States, are only found in the warmer coastal waters of Florida, south of Tampa and Miami. Caimans rarely survive winters north of central Florida, and reproduce only in southernmost Florida.
Alligators can be found in almost any type of freshwater, but population densities are greatest in wetlands with an abundant food supply and adjacent marsh habitat for nesting. In Texas, Louisiana, and South Carolina, the highest densities are found in highly productive coastal impoundments. In Florida, highest densities occur in nutrient-enriched lakes and marshes. Coastal and inland marshes maintain the highest alligator densities in Georgia, Alabama, and Mississippi. Alligators commonly inhabit urban wetlands (canals, lagoons, ponds, impoundments, and streams) throughout their range.
Alligators are exclusively carnivorous and prey upon whatever creatures are most available. Juvenile alligators (less than 4 feet [1.2 m]) eat crustaceans, snails, and small fish; subadults (4 to 6 feet [1.2 to 1.8 m]) eat mostly fish, crustaceans, small mammals, and birds; and adults (greater than 6 feet [1.8 m]) eat fish, mammals, turtles, birds, and other alligators. Diets are range-dependent; in Louisiana coastal marshes, adult alligators feed primarily on nutria (Myocastor coypus), whereas in Florida and northern Louisiana, rough fish and turtles comprise most of the diet. Recent studies in Florida and Louisiana indicate that cannibalism is common among alligators. Alligators readily take domestic dogs and cats. In rural areas, larger alligators take calves, foals, goats, hogs, domestic waterfowl, and occasionally, full-grown cattle and horses.
Allan R. Woodward. Alligator Research Biologist. Florida Game and Fresh Water Fish Commission. Gainesville, Florida 32601
Dennis N. David. Alligator Management Section Leader. Florida Game and Fresh Water Fish Commission. Gainesville, Florida 32601