CSL
Alligator mississippiensis (DAUDIN, 1801)


NAMES | DISTRIBUTION | HABITAT | STATUS | APPEARANCE | IMAGES | DIET | BREEDING | CONSERVATION

FAMILY:
ALLIGATORIDAE

A. mississippiensis
A. sinensis
C. crocodilus
C. c. apaporiensis
C. c. fuscus
C. latirostris
C. yacare
M. niger
P. palpebrosus
P. trigonatus

FAMILY:
CROCODYLIDAE

C. acutus
C. intermedius
C. johnstoni
C. mindorensis
C. moreletii
C. niloticus
C. novaeguineae
C. palustris
C. porosus
C. rhombifer
C. siamensis
M. cataphractus
O. tetraspis
T. schlegelii

FAMILY:
GAVIALIDAE

G. gangeticus

DICHOTOMOUS KEY
[German]

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STATUS OF INFORMATION:
This information was most-recently updated January 2009 and is considered up-to-date. Please contact me directly regarding updates or corrections.

COMMON NAMES:
American alligator, Mississippi alligator, Pike-headed alligator, "gator"

NAME ETYMOLOGY:
> Alligator is derived from the Spanish el lagarto which means "the lizard"
> mississippiensis means "of the Mississippi (River)", derived from mississippi + ensis (Latin for "belonging to"). In the initial description, mississippiensis was misspelt as mississipiensis (one p) but later corrected by the International Commission on Zoological Nomenclature on the principal argument that it refers to the Mississippi River

DISTRIBUTION:
[CLICK ON MAP FOR DETAILED RANGE]
Distribution map Southeastern United States: Alabama, Arkansas, North & South Carolina, Florida, Georgia, Louisiana, Mississippi, Oklahoma, Texas

HABITAT:
Primarily freshwater swamps and marshes, but also in rivers, lakes and smaller bodies of water. They can tolerate a reasonable degree of salinity for short periods of time, being occasionally found in brackish water around mangrove swamps, although they lack the buccal salt-secreting glands present in crocodiles. Construction of burrows is well documented in this species. The burrows are used for shelter and hibernation when the seasonal temperatures fall. Even outside their burrows, they can tolerate limited periods of freezing conditions (see "icing response" in Miscellaneous Facts, below). They modify their habitat through the creation of 'alligator holes', which provide a refuge for other animals during dry periods. These are excavated using both snout and tail. Once these dry out, however, the alligator crosses land in order to find another body of water. Alligators near human habitation are often seen crossing roads, entering suburbs and finding shelter in swimming pools during the drier months.

STATUS:
     CITES: Appendix II
     IUCN Red List: LRlc (LOW RISK, LEAST CONCERN)
     Estimated wild population: over 1,000,000
Summary: Widely distributed and numerous throughout most of its range.

APPEARANCE:
[click on image for enlargement]
Head drawing Adults males typically reach 4 to 4.5 metres (approximately 13 to 14.7 feet), although there are several unconfirmed reports of larger 5 m (approx 16.4 feet) and even 6 m adults (19.8 feet is the largest "reported", though there are doubts over its veracity) having been found or killed in the 19th and 20th centuries. Such sizes seem unlikely for this species. Females reach lengths of just under 3 m (approx 9.8 feet). The snout is characteristically broad, although this varies slightly between populations. Captive animals have been shown to grow significantly broader jaws compared with wild alligators, mainly due to differences in diet. When the mouth is closed, the edge of the upper jaw overlaps teeth in the lower jaw, which therefore fit into depressions in the upper jaw. This is unlike Crocodylus and Gavialis in which the lower teeth fit into depressions on the outside of the upper jaw. A bony nasal bridge is present, similar to that seen in the spectacled caiman (Caiman crocodilus) but not as pronounced. Juveniles are essentially miniature versions of their parents, although they possess bright yellow cross-bands on a black background - disruptive camouflage. More western populations (which may have been historically isolated from eastern populations) are reported to have white speckling around the jaws, with paler colouration on their bodies and tails. In all individuals, older alligators gradually lose the yellow banding and turn olive brown and black, although areas around the jaws and on the neck and belly are creamy white. The ventral surface is pale, but most scales especially nearer the tail possess significant amounts of black. Ventral osteoderms (bony plates) are present in the belly scales of all American alligators, although the extent varies between populations and the skin is considered quite valuable. The colour of the eyes is similar to many other crocodilians, being generally olive green but variable. Wild adult populations have been observed to fall into two general forms: those which are long and thin, and those which are short and stocky. Variation in growth rate, diet, climate and other factors are likely responsible for these differences.

Dentition codeDENTITION:
How many teeth does an alligator have? The diagram on the left shows a "dental formula" showing the number of teeth in different parts of the upper and lower jaws. This is not always the same, so the total number of teeth varies from 74 to 80. That breaks down into 5 pre-maxillary; 13-15 maxillary; 19-20 mandibular

IMAGES:
[click on image for enlargement]

Click Alligator habitat in Florida Everglades Click Basking alligator on grass Click Drawing of adult alligator
Click Alligator on grass behind tree Click Sub-adult basking on floating log Click Leucistic hatchling (b&w)
Click Head of large adult Click Head of swimming adult Click Front view of adult asleep on sand
Click Adult floating in water Click Sub-adult basking on floating log Click Head silhouette in water
Click Leucistic adult alligator Click Dorsal view of elongated alligator head Click Top-down view of sub-adult alligator
Click Tightly-packed sub-adults in water Click Close-up of juvenile alligator eye Click Close-up of juvenile alligator head

DIET:
Juveniles eat a wide variety of small invertebrates, particularly insects, and small fish and frogs. As they grow larger, their dietary range increases to include consequently large prey. Eventually, large adults can tackle nearly all aquatic and terrestrial prey that comes within range, although mostly this includes fish, turtles, relatively small mammals, birds and reptiles including small alligators. Alligators are, like all crocodilians, opportunistic feeders and will take carrion if it becomes available and they are sufficiently hungry. They may also expand their choice of prey to include small dogs and other pets. Alligators have been known in rare instances to attack children and even occasionally adults, usually because they mistake the human for much smaller prey, or they are provoked. In some areas, alligators are fed by humans, which is extremely dangerous and encourages alligators to approach humans aggressively expecting food. When left alone, alligators will stay away from humans and pose little threat. Feeding activity is governed by water temperature, with foraging activity ceasing if the temperature drops below 20 to 23°C (68 to 73°F).

BREEDING:
Females reach sexual maturity at an average of 1.8 m (5.9 feet). The courtship rituals, which occur when the temperatures rise in spring (this varies geographically - it is earlier further south, but the most northerly populations may not breed), have been well-studied. Both sexes communicate using aural, visual, tactile and olfactory cues. The vibrations from low-frequency
bellowing travel considerable distances in water, advertising an individual's presence. The act of rapidly swinging the head down to make contact with the water surface (head-slapping) transmits both aural and visual messages. Complex body postures communicate additional information, which is reinforced with odour from paired musk glands everted from under the chin and from the cloaca. Near the end of courtship, both animals will engage in a bout of snout and back rubbing. Overall, this courtship can last for several hours, and is thought to help synchronise both spermatogenesis (sperm production) and ovulation (release of eggs from the ovaries).

A mound nest of vegetation (usually freshly torn up) and often mud is constructed at the start of the summer, when it is both damp and warm. Nests are typically situated on banks or mats of vegetation, and one of their functions is to elevate the eggs from the water level, to reduce the chance of flooding. Flooding will kill most eggs within 12 hours of submergence. The exact location of the nest depends upon a number of factors, as chosen by the female. These are often the same sites each year, and may be close to an 'alligator hole' which was constructed by the female. Using mainly her back legs, the female excavates a conical depression in the top of her completed mound, and lays between 20 and 50 eggs (mean of 40 - 45) inside. She subsequently covers the hole with more vegetation, scooped up using her front and back legs. Occasionally, before the female begins to lay her eggs, she will abandon the site for reasons unknown - perhaps the location was not suitable in terms of its environment, or due to social reasons, but other females have been known to use such "abandoned" nests for their own clutches. The finished nest may rise 3.5 feet (just over 1 m) and be twice as wide. Females remain near the nest, in nearby water or other shelter, throughout the incubation period which averages 65 days (depending on temperature). If danger threatens, she will rapidly return to the nest to deal with the threat. Once the eggs are ready to hatch, calls from the hatchlings stimulate the mother to open the nest using her front legs and jaws to break away the vegetation. Her presence is usually essential to help break apart the hardened mud and vegetation covering the eggs, although her absence does not always spell disaster. When the eggs are revealed and the hatchlings emerge, she carries between 8 and 10 babies in her mouth down to the water, pulling her tongue down to form a pouch in which they all sit. Once in the water, she opens her jaws and shakes her head gently side to side, encouraging her babies to swim out. Once hatched, juveniles form pods (which may even include individuals from others nests) and remain close to the mother for a variable period of time - typically up to a year, but in some cases two or even three years have been reported. This affords protection in numbers at their most vulnerable life stage, and a swift response from the guardian female if they begin calling as a result of impending danger. Despite this protection, juveniles are regularly threatened by predators such as raccoons, large fish, birds and even other alligators. This cannibalism is normally from large, dominant males, and is not uncommon in many crocodilian species. Members of a pod may be found over-wintering in the same den as the adult female.

CONSERVATION:
American alligators are probably the best studied species of crocodilian, and there is a large amount of literature available on most aspects of its biology, behaviour and ecology. Population surveys are extensive and ongoing, and data are available throughout the alligators' range due to links with management and harvest programs. While populations were severely affected in the early parts of the century (with protection occurring in the early 1960's), the recovery of this species has been remarkable in most areas thanks mainly due to properly controlled and monitored conservation and sustainable use (eg. tourism, harvesting) programs. The belly skin of the alligator produces a generally high-quality leather, and this resulted in considerable hunting pressure earlier in the 20th century, particularly in Louisiana and Florida. Even after hunting was prohibited in Florida, illegal poaching continued into the 1970s. Were it not for additional changes in the law to control the movement of hides, many think extinction may have been possible. Since then, populations have improved considerably (ie. millions) and are now only considered to be threatened in a few areas by habitat degradation (including water management programs). Alligators have more recently (1979) been downgraded from IUCN listing, while CITES Appendix II classification remains to assist control in trade of other crocodilian species whose skins are similar in appearance.

In some areas, increasing alligator populations cause problems with human populations on the edge of alligator habitat, and 'nuisance alligator' programs are required to deal with them. These involve catching and removing animals which have roamed too far into human habitation, or which pose a potential threat to people. Some animals are relocated, but this has generally been shown to be ineffective as alligators often return to their home range within a matter of days. Most recent "nuisance alligator" programs either sell the animals to a farm, or use their skins to help fund the program. Given the high degree of human-alligator contact, some attacks have been reported, but these are very rarely serious. There have only been a handful of alligator-related fatalities recorded in the USA since the 1950s, and improved education and awareness is the best long-term way to avoid future incidents. An increase in recent attacks have been attributed to illegal feeding of alligators, making them less wary of humans, bolder, and more likely to attack instead of flee.

Large-scale captive and wild sustainable harvest programs (eg. over 150 farms) are well established in several states (e.g. Florida, Louisiana, Texas). This involves captive rearing, ranching and direct cropping of wild populations (eggs and adults), but all linked to proper monitoring programs. The difference between the historical hunting that nearly led to extinction and modern harvest programs is simple: today, there are very strict quotas and controls that prevent wild populations from being adversely affected. Alligators have proven themselves to be highly resilient to both natural and induced mortality, and harvest has many indirect conservation benefits not just for alligators but for entire habitats. Cropping is only allowed from certain populations, protecting peripheral populations that are still recovering. Ranching programs usually have to return a high percentage (17% in Louisiana) of juveniles back into wild populations, although recovery in these areas has now been documented and further reintroduction is likely unnecessary. Alligators have been successfully reintroduced or restocked in several states (e.g. Arkansas, Mississippi). Alligator hunting is allowed in several states under strict quota or licence guidelines. In Florida, the results of harvesting have shown that up to 13% of subadult to adult animals, plus all the eggs from 50% of all located nests, can be safely removed from the alligator population annually without affecting population stability. These kinds of figures are vitally important for proper management programs for alligators and other species.

Several areas of research still require attention, including more work on population dynamics. Much has been learned in the last few years, but management programs rely upon a sound grasp of what populations do in the wild under different circumstances. The state of the wild alligator populations provides ample opportunity for such research to be undertaken. An examination of the effects of cropping and ranching is also possible. Other research taking place involves looking at captive husbandry techniques. These findings have implications for other crocodilian species. Although habitat modification is often to the detriment of crocodilians, proper management can benefit local populations. In Louisiana, weirs and impoundments have been constructed to allow for better water and salinity control of areas of marshland. Increased alligator populations are the result in areas where these controls have been implemented.

Alligators have been shown to be an important part of their ecosystem, and are thus regarded by many as a 'keystone' species. This encompasses many areas from control of prey species to the creation of peat through their nesting activities. Several other species benefit from the presence of alligator nests, not least the Florida Red-bellied turtle (Chrysemys nelsoni) which incubates its own eggs there (up to 200, from more than one individual). The creation of 'alligator holes' is of great value not only to the alligators, but to the other species of animals which use them. For these animals, the value of the refuge outweighs any additional risks from their creators. Alligators in some areas are also showing greatly increased levels of mercury, an indicator of the state of the ecosystem. This may have long-term implications for their ability to reproduce, but the effects are still being quantified.

MORE INFORMATION:
For more information on conservation initiatives for this species, see the CSG
Action Plan resource.

MISCELLANEOUS FACTS:

  • American alligators hibernate during the winter in burrows (or "dens") that they construct, but may occasionally emerge during brief spells of warmer weather.
  • Alligators do not feed during the cooler months. Studies in captivity have shown that alligators generally begin to lose their appetite below 27°C (80°F), and stop feeding altogether below 23°C (73°F). They can easily last the winter on their energy reserves.
  • Adult alligators can survive freezing conditions if they are in water. They submerge their body but keep their nostrils projecting above the water surface, so that when the surface freezes they can still breathe (called the "icing response"). Essentially their upper body becomes trapped in the ice. However, occasionally alligators may be trapped completely below ice, and have been known to survive for over 8 hours without taking a breath, because the freezing water slows their metabolic rate down to very low levels. Yet another example of their amazing ability to survive.
  • As of May 2006, there have been 19 confirmed fatalities caused by alligators in the State of Florida since records began in 1948.

    SIGNIFICANT REFERENCES:

  • Brandt, LA (1991). Long-term changes in a population of Alligator mississippiensis in South Carolina. J. Herpetol. 25(4): 419-424
  • Brisbin, IL, Ross, CA, Downes, MC, Staton, MA & Gammon, B (1986). A Bibliography of the American Alligator. Savannah River National Environmental Research Park. 310 pp.
  • Brisbin, IL, Standora, EA & Vargo, MJ (1982). Body temperature and behavior of American alligators during cold winter weather. Am. Midl. Nat. 107: 209-218
  • Elsey, RM, Joanen, T & McNease, L (1994). Louisiana's alligator research and management program: an update. In: Crocodiles. Proceedings of the 12th Working Meeting of the Crocodile Specialist Group. IUCN, Gland, Switzerland. pp. 199-229
  • Garrick, L, Lang, J & Herzog, HA (1978). Social signals of the American alligator. Bull. Amer. Mus. Nat. Hist. 160: 155-192
  • Hunt, RH, Ogden, JJ (1991). Selected aspects of the nesting ecology of American alligators in the Okefenokee swamp. J. Herpetol. 25(4): 448-453
  • Hunt, RH & Watanabe, ME (1982). Observations on the maternal behavior of the American alligator, Alligator mississippiensis. J. Herpetol. 16(3): 235-239
  • Kushlan, JA, & Simon, JC (1981). Egg manipulation by the American alligator. J. Herpetol. 15(4): 451-454
  • Lee, JR, Burke, VJ, & Gibbons, JW (1997). Behavior of hatchling Alligator mississippiensis exposed to ice. Copeia 1997(1): 224-226
  • McIlhenny, EA (1935). The Alligator's Life History. Christopher Publishing House, Boston.
  • Rootes, WL, Chabreck, RH (1993). Reproductive status and movement of adult female alligators. J. Herpetol. 27(2): 121-126
  • Vliet, K (1989). Social displays of the American alligator (Alligator mississippiensis). Amer. Zool. 29: 1019-1031
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