American alligators are found from the southern Virginia-North Carolina border, along the Atlantic coast to Florida and along the Gulf of Mexico as far west as the Rio Grande in Texas. (Britton, 1999)
American alligators are usually found in freshwater swamps, marshes, rivers, lakes, and occasionally, smaller bodies of water. It is believed that this preference for calm waters has to do with their swimming and breathing. In areas of protected water, an American alligator has only to keep its nasal disk above water to breath, whereas in rough water the snout must be at a steeper angle, making it more difficult to swim. They can also tolerate reasonable amounts of salinity, but only for short amounts of time due to their lack of buccal glands. (Britton, 1999; Ross, 1989)
American alligators are also known to modify their enivironment by creating burrows. These are created using both snout and tail and are used for shelter and hibernation during freezing temperatures. If the water they live in dries out, alligators will swim or walk to other bodies of water, sometimes even taking shelter in swimming pools. (Britton, 1999)
The average size for an adult female is just under 3 meters (9.8 feet), while the adult male usually falls between 4 and 4.5 meters (13 to 14.7 feet). American alligators reaching lengths of 5-6 meters (16 to 20 feet) have been reported in the past, but there have been no recent recordings equaling those lengths. (Britton, 1999; Ross, 1989)
Legs of American alligators are characteristically short, though capable of carrying the animal at a gallop. The front legs have five toes while the back legs have only four. The snout of this alligator species is also distinct, being significantly broader for those in captive, mainly due to a difference in diet. (Britton, 1999)
Nostrils at the end of the snout allow for breathing while the alligator is otherwise fully submerged beneath the water's surface. During times of hibernation, alligators keep these nostrils just above the water's surface, allowing the top part of the body to freeze in ice. The large fourth tooth in the lower jaw fits into a socket in the upper jaw and is not visible when the mouth is closed. (Britton, 1999)
Both males and females have an "armored" body with a muscular flat tail, used in propelling the animal forward while swimming. The skin on their back is armored with embedded bony plates called osteoderms or scutes. Adult males and females have an olive brown or black color with a creamy white underside. The young can be distinguished from adults because they have bright yellow stripes on their tails. Eye color of American alligators is generally silverish. (Britton, 1999; Ross, 1989)
- Sexual Dimorphism
- male larger
The temperature at which American alligator eggs develop determines their sex. Those eggs which are hatched in temperatures ranging from 90 to 93 degrees Fahrenheit turn out to be male, while those in temperatures from 82 to 86 degrees Fehrenheit end up being female. Intermediate temperature ranges have proven to yield a mix of both male and females. After hatching, alligators can grow rapidly, espectially during the first four years of life, averaging over 1 foot of growth for each year of life. Both sexes reach sexual maturity at around 6 feet in length, however, this occurs earlier in males because they reach this length sooner than females. (; Ross, 1989)
- Development - Life Cycle
- temperature sex determination
Breeding takes place during the night, in shallow waters. Females usually initiate courtship during peak activity. When males (bulls) wish to attract females, they often roar or bellow, emmitting subaudible vibrations which can be seen by the bubbles and ripples they produce. Other courtship rituals include rubbing, touching, blowing bubbles, and vocalizing. It is also common for males to raise their heads out of the water, exposing their vulnerable necks as an expression of "good intentions". It is also quite common for both partners to try and push one another underwater in an attempt to judge eachothers strength. (; Ross, 1989)
Alligators are not monogamous, but rather, polygynous, which means one male may service up to ten or more females in his territory. This maximizes chances for successful breeding. Male alligators are territorial animals during the breeding season, and will defend their area against other male intruders, often displaying acts of headramming and sparring with open jaws. (; Ross, 1989)
- Mating System
Both males and females reach sexual maturity when they are about six feet long, a length attained at about 10 to 12 years, earlier for males than females. Courtship starts in April, with mating occuring in early May. After mating has taken place, the female builds a nest of vegetation. Then, around late June and early July, the female lays 35 to 50 eggs. Some females have been reported as laying up to 88 eggs. The eggs are then covered with the vegetation nest through the 65-day incubation period. (Britton, 1999; )
Towards the end of August, the young alligators begin to make high-pitched noises from inside of the egg. This lets the mother know that it is time to remove the nesting material, and the six to eight inch alligator is hatched. Newly hatched alligators live in small groups, call "pods." Eighty percent of young alligators fall victim to birds and raccoons. Other predators include bobcats, otters, snakes, large bass and larger alligators. Females have been known to aggressively defend their young during these first few months and, in some cases, years. Maturity is generally reached during the sixth year. (Britton, 1999; )
- Key Reproductive Features
- gonochoric/gonochoristic/dioecious (sexes separate)
- Breeding interval
- American alligators breed once yearly.
- Breeding season
- Breeding occurs in early May, with egg laying occuring in late June and early July.
- Range number of offspring
- 35 to 88
- Range age at sexual or reproductive maturity (female)
- 10 to 12 years
- Range age at sexual or reproductive maturity (male)
- 10 to 12 years
Males provide no parental care, and parental care by the female is limited to the first year of life. She is responsible for removing any vegetation covering the nest when her young are ready to hatch, and she will often bring them to water after hatching. During the first year or so she will defend her hatchlings from predators. After the first year, the female leaves her young to tend to new hatchlings of the next breeding season. ()
- Parental Investment
While there are currently no methods for determining the age of an alligator while still alive, it is known that those in the wild tend to live to between 35 and 50 year, while those in captive generally live longer, around 65-80 years. Factors which can lead to earlier mortality include successful predation early in life and hunting by humans. ()
- Typical lifespan
- 35 to 50 years
- Typical lifespan
- Typical lifespan
- 65 to 80 years
- Typical lifespan
Young alligators remain in the area where they are hatched and are generally a social species when young. This method of group living is associated with greater protection from predators. Adults do not display such close knit bonds, however, they do tend to associate loosly in social groups. When forced to live in tighter areas as a result of drought, though, these animals tend to ignore each other. (Britton, 1999; Levy, 1991; Ross, 1989)
American alligators undergo periods of dormancy when the weather becomes cold. They may excavate a cave in a waterway and leave a portion of it above water during this time. In areas where water level fluctuates, alligators dig themselves into hollows in the mud, which fill with water. These tunnels are often as long as 65 feet and provide protection during extreme hot or cold weather. (Britton, 1999; Levy, 1991)
Perhaps the most interesting aspect of alligator behavior is its means of locomotion. Besides swimming, American alligators walk, run, and crawl. Most often they will use a "high walk". In this walk alligators keep their legs almost directly beneath them, as opposed to most reptiles which keep their legs to the sides at a diagonal. This "high walk" results in greater elevation, allowing alligators to almost entirely lift their tales up off of the ground. (Ross, 1989)
When alligators wish to increase speed they diagonally opposite limbs move forward almost simultaneously. This allows for faster movement, but it also decreases the animal's stability. When the eqilibrium is lost an alligator begins moving in a new way, moving its limbs out to the sides and crashing onto its chest. In this manner an alligator quickly crawls along. This method of movement is most useful when going down steep shorelines into the water. (Ross, 1989)
Female alligators usually remain in a small area. The males occupy areas greater than two square miles. Both males and females extend their ranges during the courting and breeding season. (Britton, 1999; Levy, 1991)
Communication and Perception
American alligators are the most vocal of all crocodilians, and communication begins early in life, while alligators are still in eggs. When they are ready to hatch, the young will make high pitched whining noises. Alligators commonly bellow and roar at one another. The bellow is loud and throaty, and can be heard from up to 165 yards away. Alligators also emit sounds called chumpfs. These are cough like purrs made during courting. (; Levy, 1991; Ross, 1989)
Other communication during mating season includes non-verbal forms such as lifting the head out of the water to show honorable intentions, headslapping by males as a sign of aggression to ward off intruders, and perhaps most notably, the virbrations, bubbles, and ripples seen in the water as a result of subaudible noises.
Alligators are basically carnivores, but they eat more than just meat, feeding on anything from sticks to fishing lures to aluminum cans. Mostly, they consume fish, turtles, snakes, and small mammals. When they are young they feed on insects, snails, and small fish. (Britton, 1999; Levy, 1991)
Alligators hunt primarily in the water at night, snapping up small prey and swallowing it whole. Large prey are dragged under water, drowned and then devoured in pieces. Alligators have also been known to hold food in their mouth until it deteriorates enough to swallow. They also have a specialized valve in the throat called a glottis, which allows them to capture prey underwater. ()
With regards to hunting animals on land, alligators are usually considered idle hunters, waiting offshore for unsuspecting prey to drink at the water's edge. With this approach an alligator is likely to grab the drinking animal's head, slowly pulling it underwater until it drowns. In this way alligators exert minimal energy in capturing prey.
- Animal Foods
- Plant Foods
- wood, bark, or stems
The first few years of a hatchlings life are the most dangerous, as anything that can eat a small alligator will. Snakes, wading birds, osprey, raccoons, otters, large bass, garfish, even larger alligators will feed upon young alligators. Once the alligator reaches about 4 feet, its only real predator is man. Extremely thick skin protected by bony plates called scutes prevent harm from most attacks. It is this skin, though, which attracts man to alligators. It is commercially used for the creation of wallets, purses, boots, and other textiles. (; Ross, 1989)
American alligators have proven to be an important part of the environment, and therefor, are considered by many to be a "keystone" species. Not only do they control populations of prey species, they also create peat and "alligator holes" which are invaluable to other species. Red-bellied turtles, for example, incubates its own eggs in old alligator nests. Alligators also are good indicators of environmental factors, such as toxin levels. Increased levels of mercury have been found in recent blood samples. (Britton, 1999)
- Ecosystem Impact
- creates habitat
- keystone species
Economic Importance for Humans: Positive
Alligators are hunted mostly for their skin, but also they are hunted for their meat. Today, there is a multimillion dollar industry in which alligators are raised in captivity for the production of their meat and skin. Also, alligators are a tourist attraction, especially in Florida.
Economic Importance for Humans: Negative
Since the alligator will feed on almost anything, they pose a threat to humans. In Florida, where there is the greatest alligator population, there were five deaths to alligator attacks from 1973 to 1990. Dogs and other pets are also sometimes killed. (University of Florida)
American alligators are listed as threatened by the federal government because they are similar in appearance to American crocodiles (Crocodylus acutus). American crocodiles are endangered and the government does not want hunters to confuse the two species. Hunting is allowed in some states, but is is heavily controlled.
Lauren Pajerski (author), Undergraduate Research Opportunity Program, University of Michigan.
Benjamin Schechter (author), University of Michigan-Ann Arbor, Robin Street (author), University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
uses sound to communicate
living in landscapes dominated by human agriculture.
- bilateral symmetry
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- brackish water
areas with salty water, usually in coastal marshes and estuaries.
an animal that mainly eats meat
the nearshore aquatic habitats near a coast, or shoreline.
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
A substance that provides both nutrients and energy to a living thing.
mainly lives in water that is not salty.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
- keystone species
a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).
marshes are wetland areas often dominated by grasses and reeds.
having the capacity to move from one place to another.
specialized for swimming
- native range
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an animal that mainly eats fish
having more than one female as a mate at one time
associates with others of its species; forms social groups.
living in residential areas on the outskirts of large cities or towns.
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU).
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
living in cities and large towns, landscapes dominated by human structures and activity.
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
Levy, Charles K. 1991. Crocodiles and Alligators. The Apple Press. London. Pages 8-22, 59.
National Audobon Society Field Guide to North American Reptiles and Amphibians; 1994.
Britton, A. 1999. "Alligator mississippiensis in the Crocodilians, Natural History and Conservation" (On-line). Accessed 31 March 2000 at http://www.flmnh.ufl.edu/cnhc/csp_amis.htm.
Levy, C. 1991. Crocodiles and Alligators.. London: The Apple Press.
Ross, C. 1989. Crocodiles and Alligators. New York, New York: Facts on File, Inc..