Alligator mississippiensis (American Alligator)

Περιγραφή

Geographic Range

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.

Habitat

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. 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.

Physical Description

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. 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. 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. 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.

Development

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.

Reproduction

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. 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. 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. 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. 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.

Lifespan/Longevity

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.

Behavior

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. 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. 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. 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.

Home Range

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.

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.

Food Habits

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.