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Alligator mississippiensisAlligator, Gator, American alligator, Florida alligator, Mississippi alligator, Louisiana alligator.

By Katharyn Seay

Geographic Range

Alligator mississippiensis is a crocodilian native to North America and is the crocodilian with the northernmost distribution worldwide. These creatures are found as far north as the tidal regions in North Carolina (35 degrees N latitude), to as far south as every county in Florida, and as far west as central Texas. Other states where the American alligator can be found are South Carolina, Georgia, Alabama, Mississippi, Louisiana, Arkansas, and Oklahoma. In some cases, formerly captive American alligators have been released into states outside of their geographic range. A few examples of these non-native states are California, New Jersey, and Virginia. However, their existence is short-lived. (Ouchley, 2013)

Habitat

Although sometimes found in brackish water settings, the American alligator is most commonly found in freshwater environments of the temperate region due to its low tolerance for salt. The most common areas to observe the American alligator are in marshes, swamps, rivers, ponds, and lagoons. The American alligator has also been known to occupy man-made water structures such as swimming pools, fishponds, and dammed lakes in urban and suburban areas.

An alligator can make a structure known as a gator hole in the ground. These holes are made by the alligator using its snout and tail to burrow into the mud or soil until a suitable space is created. This gator hole is created as a safe haven against drought and irregular weather patterns.

Although the American alligator is sometimes seen on land, it is primarily an aquatic creature. There are two main factors that contribute to habitat inclination for the American alligator. The first factor depends on the sex of the alligator because the female is more interested in protecting her young than the male. A male alligator spends the majority of his time in open waters, while the female only ventures into open water during mating season. The second factor is based on size. The smaller the alligator, the more likely it is to be found in wetlands, where it uses the plant life as a means of protection from predators. Whereas the larger the alligator, the more likely it is to be found in open waters. (Bartlett and Bartlett, 2006; Campbell and Mazzotti, 2004; Neill, 1971)

Physical Description

As a hatchling, an alligator is typically 22.9 cm long. Until it is 91.4 cm long, both a male and female alligator will grow at similar rates. However, once this length is attained, a female will continue to grow at a slower rate than a male. Consequently, as a characteristic of sexual dimorphism, a male adult alligator is larger than a female alligator. A male alligator has an exponential growth rate until it is 20 years of age. By this time a male alligator is approximately 350.5 cm. In the female, after 20 years, lengths average 256.5 cm. A female is predicted to have stopped growing at age 45 with a length of 274.3 cm. It is estimated that a male alligator stops growing at a length of 365.8 cm. The tail of the American alligator accounts for half of its overall body length. The weight of the American alligator depends on habitat, what food is available, and sex, but the average weight is 150 kg. In the United States the largest recorded alligator was found in 1998 in Jackson County, Texas at 436.9 cm and weighing 408.23 kg.

The American alligator is the darkest alligator in the crocodilian family. As a juvenile, the American alligator is black with yellow cross bands. As an adult, the yellow color fades and the alligator is an olive black color.

The American alligator is the largest reptile in the United States. While it is quite large, its limbs are relatively short and thick to help it swim. Another distinguishing feature of the American alligator is its jaw structure and overall shape of the rostrum. As compared to the pointed shape of the crocodile snout, the snout of the American alligator is round. Because the upper jaw is larger than the lower jaw, when an alligator closes its mouth, no teeth are visible, as compared to the visibility of teeth when a crocodile has a closed mouth. The American alligator is a homodont and has approximately 80 teeth of all the same size, but because the teeth break, get worn down, or fall out, the teeth are replaced rapidly throughout its lifetime. (Bartlett and Bartlett, 2006; Brunell, et al., 2013; Carpenter and Lindsey, 1980; Erickson, 1996; Neill, 1971)

  • Sexual Dimorphism
  • male larger
  • Range mass
    91 to 360 kg
    200.44 to 792.95 lb
  • Average mass
    150 kg
    330.40 lb
  • Range length
    257 to 437 cm
    101.18 to 172.05 in
  • Average length
    350 cm
    137.80 in
  • Average basal metabolic rate
    0.1539 W
    AnAge

Development

The sex of the American alligator is temperature-determinant. The sensitive temperature interval for sex determination is 25 to 30 days after the eggs have been laid. A female hatchling is formed when the incubation temperature is 31 degrees C or below. A male is formed when the incubation temperature is 33 degrees C or higher. At 32 degrees C an even ratio of male and female hatchlings are produced.

After the egg is laid, it takes approximately two months for it to hatch. The egg is an ovoid shape with the alligator wrapped inside. To help the alligator emerge when it hatches, it has an egg tooth to help break through the shell. At the time of hatching, the alligator is approximately 20.3 cm in length. During the first few days post-hatching, the alligator uses the unabsorbed egg yolk inside its belly as nourishment. A scar might be visible on its underside where the egg membranes were attached. By the time the hatchling is about three months old, it goes into the water for winter retreat and the scar disappears. A baby alligator is white when it hatches and later develops the dark green-brownish adult coloration

Not all eggs will make it to hatching because of fire, floods, and mothers crushing them. Neill (1971) reported, out of 35 hatchlings, only four would reach adulthood. An alligator that does survive will continue to grow in length until it reaches a length of 1.83 meters. This takes between 10-20 years, which has a direct correlation with sexual maturity. It has a determinate growth system, meaning after a certain age, it eventually stops growing.

When an alligator is less than 0.9 meters long it is possible to look for external genitalia to determine the sex. Relative to age, a larger alligator usually indicates a male and a smaller alligator indicates a female. (Ferguson and Joanen, 1983; Neill, 1971; Woodward, et al., 2011)

  • Development - Life Cycle
  • temperature sex determination

Reproduction

The American alligator is a polyandrous animal, meaning one male alligator can mate with several females. However, one male usually mates with just one female per breeding season. Each season, a male will breed with a different female. A male alligator will confront other alligators over its spaces because it feels a threat for space preservation. According the Neill (1971), when one male alligator confronts another male alligator, the confrontation has a specific process it follows. Each alligator opens its mouth wide, lunges its body upward, and attempts to be louder than the other. At this time, a hissing sound is produced instead of a bellow. Once the eggs have been laid, both sexes bellow, sometimes in a choral circle, to claim territory among other alligators in the area.

The search for finding a potential mate starts in the spring. Both the male and female alligators participate in this process. This process can be time-consuming because each alligator has to find a mate that is fitting for its size, age, and readiness to mate. In both sexes, a trail is made by the excretions from the anal glands. This trail of courtship pheromones makes it easier for an alligator to find a potential mate.

After the pheromone trail is laid down, the male begins bellowing, as a method to minimize crowding by males in the area. While a female alligator concentrates activity where her nest is located, the male alligator seeks an area where he can mate. Every year, the adult alligator will mate and nest in the same general areas. The main change that occurs in spatial distribution is with a female alligator that protects her nesting area from the previous year, which may occasionally increase in area. (Mason and Rockwell Parker, 2010; Neill, 1971)

American alligators reproduce sexually, with internal fertilization. Because alligators are oviparous, after fertilization takes place, the female alligators lays eggs. American alligators are seasonal breeders and breed once each year. The breeding season starts in April and lasts throughout June. Eggs typically hatch within 60 days.

Alligators can produce 2-58 offspring at a time. Because they are iteroparous, the eggs are produced in more than one clutch. The average number of eggs produced is 39 per clutch. Eggs are laid at night which can last an hour in duration. The eggs are generally the size of a goose egg, which average 4 cm in length and 17.78 cm in diameter, and are white and translucent. The clutch of eggs is all laid at one time with the amount of eggs that are produced positively correlating to the size of female alligators. The eggs incubate in a nest for a period of 65 to 70 days. During this time, female alligators don’t stay directly on the nest the whole time. Instead, they stay close by to try and fend off any raccoons, Procyon lotor, or other predators. After the eggs are hatched, the average birth mass of the hatchlings is 65 g. While they are growing and developing, they usually spend the first year of their lives with the mothers, and then they become independent. Sexual maturity is not measured by years in American alligators, but rather by reaching a length of 1.83 meters. It usually takes females 10 to 20 years to reach this length and males 10 to 18 years. Age at sexual maturity is influenced by growth factors, such as habitat, food availability, and geographic range. (Erickson, et al., 2003; Lance, 1989; Neill, 1971; Ouchley, 2013)

  • Breeding interval
    American alligators breed once yearly.
  • Breeding season
    American alligators start courting in April. Mating season continues until the eggs are laid in early June. The eggs typically hatch 60 days after they are laid.
  • Range number of offspring
    2 to 58
  • Average number of offspring
    39
  • Average time to independence
    1 years
  • Range age at sexual or reproductive maturity (female)
    10 to 20 years
  • Range age at sexual or reproductive maturity (male)
    10 to 18 years

The female American alligator is the only parent that exhibits parental care to offspring. The male doesn’t invest any time or effort, but he may stay near the nest. The female is protective of her new hatchlings from the pre-hatchling stage up until the pre-weaning stage, which usually lasts a year after the eggs have hatched.

The female alligator starts building her nest in early summer. She selects an area that already has debris, leaves, mud, and vegetation. The vegetation and other plant materials, which are used for shade, are formed to make a nest that is 3-5 meters from the water’s edge. The female builds the nest using her tail and doesn’t gather anything using her mouth. If the material is not within 4.6 meters away she doesn’t retrieve it; instead she uses what is immediately available in the location.

After the eggs are laid, the female covers the nest so it is sheltered from the environment. She doesn’t sit directly on top of her nest due to the potential of crushing the eggs. Instead, she will remain within 3 meters of the nest. The only time a female might stray form the nest is when predation pressure is high. If she leaves to avoid predation, her nest is vulnerable.

Because the eggs are temperature-sensitive, the female alligator will ensure the nest is near a damp area that is close to a water source and will dampen the nest as necessary.

The female alligator can leave her hatchlings while they are still in the eggs if food becomes an immediate necessity for her, or if the nest is no longer identifiable to predators. If she stays past this period, she doesn’t stay with her young for more than a year, at which time they become independent. (Hunt and Watanabe, 1982; Neill, 1971)

  • Parental Investment
  • female parental care
  • pre-hatching/birth
    • protecting
      • female
  • pre-weaning/fledging
    • protecting
      • female

Lifespan/Longevity

It is estimated that an American alligator can typically live 20-30 years in the wild, whereas in captivity, it can live approximately 50 years. The longest recorded time for an alligator living in the wild was 56 years, and longest lifespan recorded in captivity was 73.1 years. (Caspari and Robbins, 2003; Potts, 1998)

Behavior

American alligators are social animals, and live in groups. The hatchlings are more social than the adults. The new hatchlings tend to stay together because closeness is a beneficial defense against potential predators; there is safety in numbers. Adult alligators tend to inhabit smaller, close-knit groups, rather than large social circles. Their activities take place diurnally and seasonally, being most active in the spring. As ectotherms, American alligators bask in the early morning. In early spring, basking continues longer into the day than during the summer months, when basking occurs earlier in the morning and later in the afternoon. Due to winter’s temperature limitations, basking occurs throughout the whole day.

These alligators are territorial, motile animals. American alligators are fossorial and make holes in the ground to live in during extreme conditions. These holes can be very large and act as a barrier of protection in times of extreme cold or hot temperatures or irregular weather patterns, such as droughts and tropical storms.

American alligators are natatorial. However, when these creatures walk on land, they exhibit a movement called a high walk. This behavior includes walking on all fours, in a very slow motion with their tail dragging the ground. This is a low energy form of mobility. (Garrick, et al., 1978; Neill, 1971; Ouchley, 2013; Willey, et al., 2003)

  • Range territory size
    409000 to 689000 m^2

Home Range

Male alligators inhabit larger areas than female alligators. The average home range for female alligators is 40,900 m^2, while the home range of male alligators is 68,900 m^2. The alligators defend this entire home range as their territory. (Lewis, et al., 2014)

Communication and Perception

The American alligator can communicate using airborne and waterborne frequencies. One hundred Hz to 2,000 Hz is the frequency range an alligator can respond to in water, with 800 Hz as the peak sensitivity point. One hundred Hz to 8,000 Hz is the frequency range an alligator is able to respond to in air, with 1,000 Hz as the peak sensitivity point. Also during mating season, the male American alligator makes a low pitch frequency bellow type sound by sucking in air because it has no vocal cords to attract potential mates. This bellowing can have varied duration, but it is usually loud and deep in tone to ward off any other males in the area.

The American alligator is known to be a vocal creature throughout its lifetime. Even alligator hatchlings make high pitched screeching noises as a distress call. These calls have a frequency of as high as 1KHz to as low as 50 Hz. As these signals are heard, any adult alligator in the area will come to the scene to make sure the juveniles are safe.

It is more difficult for the alligator to communicate through waterborne signals. To communicate in water, an alligator communicates by slapping the water. During mating season, the male alligator does a head slap on the water to send signals out to the female alligator. Because sound travels faster in water, the head slap technique can allow long-distance communication. Infrared vibrations are more difficult to perceive than other waterborne signals. As a result, the head slap is combined with the infrared signals for easier recognition. The infrared signals are used to detect size and strength of an animal in detection, whereas the slap is used to perceive where exactly the animal is located.

Integumentary sense organs (ISO) are features of an alligator to help it perceive its environment. These ISOs can be found in the jaws or scales of the alligator. The ISOs help the American alligator sense movements in the water, tell it when prey is in contact with the teeth, and help identify what item it has in its jaw at a certain time. An alligator's eyes are located on the side of its head to help it perceive its environment. As it swims through the water its eyes are always above the water surface to also aid in the process of perception of surroundings. (Dinets, 2013a; Dinets, 2013b; Higgs, et al., 2002; Leitch, 2012; Riede, et al., 2011)

Food Habits

The diet of the American alligator is varied. Two main factors that contribute to the food habits of the American alligator are its size and stage of development. The bigger the alligator, the more it can eat in terms of volume and the bigger animals it can eat. Even in the adult stage, size of the adult affects what they eat; larger adults consume larger prey in greater volume. From neonate to juvenile to adult, the American alligator grows in size, but the distal limbs actually decrease in terms of relative size. This potentially forces the alligator to spend almost all of its time in the water, where in turn it will consume more aquatic animals. During the juvenile life stage, an alligator eats mostly small fish, insects, and invertebrates. As the alligator matures, it starts to eat larger mammals. As an adult, an alligator can also eat reptiles and birds.

The American alligator is classified as a generalist carnivore. Saalfeld et al.(2011) conducted a diet study in Texas, and found that invertebrates comprise 15.7-34.6% of the alligators’ diets, while amphibians and reptiles made up 11.9-26%, and mammals 2-11.4%. The remainder of the diet included birds and fish (0-11.3%). A few examples of animals consumed are Micropterus salmoides (largemouth bass), Lepisosteus oculatus (spotted gar), Margaritifera margaritifera (freshwater pearl mussel), Hyla cinerea (green tree frog), Kinosternon flavescens (yellow mud turtle), Agkistrodon piscivorus (water moccasin), Gallinula chloropus (common moorhen), and Sus scrofa (feral hog).

If an alligator's primary food resource is not available, it will sometimes feed on carrion and non-prey items such as rocks and artificial objects, like bottle caps. These items help the alligator in the process of digestion by crushing up the meat and bones of animals, especially animals with shells. (Kerfoot, et al., 2014; Lutterschmidt and Wasko, 2006; Ouchley, 2013; Saalfeld, et al., 2011)

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • fish
  • carrion
  • mollusks

Predation

Many animals are predators of American alligator eggs and hatchlings. The dominant egg predators are raccoons Procyon lotor, which are found throughout the range of the alligators. There are also many nest predators, including black bears Ursus americanus, Virginia opossums Didelphis virginiana, river otters Lontra canadensis, feral hog Sus scrofa, and American crows Corvus brachyrhynchos. Birds, such as great blue herons Ardea herodias, are also predators to young alligators along with larger American alligators. Humans, Homo sapiens, also have a substantial impact on American alligators, killing them intentionally and unintentionally.

Alligator skin is used as a protective mechanism against predators. It is thick and has bony scutes called osteoderms underneath the skin. These scutes are similar to bone, providing a tough barrier on the skin to help when defending from predators. (Chen, et al., 2013; Ouchley, 2013)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

The American alligator is a host for the ectoparasite, the sea turtle barnacle Chelonibia testudinaria. The attachment formed between the hardened keratinized portions of the osteoderms of the American alligator and the sea turtle barnacle Chelonibia testudinaria is the first time successful attachment was made using this method. Nifong and Frick (2011) report that this is an infrequent ectoparasitic relationship known because only two cases have been documented.

Two endoparasites of the American alligator are root-knot nematodes, Meloidogyne incognita, and pentastomids, Sebekia mississippiensis. Freshwater leeches, Macrobdella decora, and American dog ticks, Dermacentor variabilis, are other known ectoparasites. According to Nifong and Frick (2011), the ectoparasites can harm the eardrum, cloaca, and epidermis. They cause damage to these parts by acting as a haven for harmful bacteria and causing destruction to the blood capillaries. (Nifong and Frick, 2011)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Humans (Homo sapiens) hunt alligators for meat, skin, and teeth. The meat is eaten, the skin is mostly used for manufacturing purposes, such as making boots or jackets, and the teeth are used to make jewelry, buttons, and cane handles. The oils of relatives in the order Crocodilia are also used as antimicrobial or anti-inflammatory to help cure skin aliments through the use of fatty acids produced by these animals. Alligators are also a tourist attraction in many zoos, which contributes to ecotourism, especially in Florida. (Buthelezi, et al., 2012; Neill, 1971)

Economic Importance for Humans: Negative

American alligators can cause harm or death to humans. According to Ouchley (2013), between 1948 and 2005, 337 attacks occurred in Florida, 15 in Texas, 9 in Georgia, 9 in South Carolina, 5 in Alabama, 2 in Louisiana, and 1 in North Carolina. Ouchley also reported that in Florida between 1948 and 2012, 22 of the 344 attacks were fatal.

Alligators that are 2.74 meters long or larger are to blame for the most attacks. Attacks can happen throughout the year, and typically occur when people are swimming or destroying the alligators’ natural habitat by building homes and other manmade structures. (Ouchley, 2013)

  • Negative Impacts
  • injures humans

Conservation Status

Inadvertently, humans (Homo sapiens) kill alligators by running over them with vehicles, catching them in nets and trout-lines, and striking them with boats in shallow waterways. Along with hunting, these threats contributed to the American alligators being listed as federally endangered.

In 1966, American alligators were first listed under the Endangered Species Preservation Act of 1966 in hopes restoring habitat. However, this effort was not successful. Alligators also were listed as endangered when the Endangered Species Act of 1973 passed. After many years of habitat preservation and increasing alligator numbers, American alligators were delisted and the population of alligators has since fully recovered. The IUCN red list lists the American alligators as a species of least concern. On the on-line US federal list they are still listed as threatened, but as other research provides, they are no longer a listed species. They are also listed as appendix II of CITES, which means even though they are not a threatened species currently; if trade is not controlled properly they could return to a threatened state. Certificates and permits are also required for the export and import of the alligators under appendix II of CITES. (Crocodile Specialist Group, 1996; Moyle, 2013; Ouchley, 2013)

Contributors

Katharyn Seay (author), Radford University, Karen Powers (editor), Radford University, April Tingle (editor), Radford University, Emily Clark (editor), Radford University, Cari Mcgregor (editor), Radford University, Jacob Vaught (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

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.

World Map

acoustic

uses sound to communicate

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.

carnivore

an animal that mainly eats meat

carrion

flesh of dead animals.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

drug

a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease

ecotourism

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.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

freshwater

mainly lives in water that is not salty.

infrared/heat

(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

suburban

living in residential areas on the outskirts of large cities or towns.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

temperate

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).

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

threatened

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).

urban

living in cities and large towns, landscapes dominated by human structures and activity.

vibrations

movements of a hard surface that are produced by animals as signals to others

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