Identification: Alligator mississippiensis is a robust crocodilian with a total length of 1.8-5 m (6-16.5 ft), and a record length of 5.84 m (19 ft 2 in) (Conant and Collins, 1998). American alligators can be distinguished from Crocodylus acutus, the American crocodile, and Caiman crocodilus, common caiman, by the presence of a broad, rounded snout, without conspicuous teeth protruding while the mouth is closed (especially the lower 4th tooth) (Behler and King, 1979; Conant and Collins, 1998; Powell et al., 1998). Unlike C. crocodilus, alligators lack a prominent bony ridge in front of and between the eyes (Behler and King, 1979; Conant and Collins, 1998; Powell et al., 1998). See the species accounts titled "Crocodylus acutus (Cuvier, 1807)" and "Caiman crocodilus (Linnaeus, 1758)" on this website for comparison. The general dorsal coloration is black, but light juvenile markings may be present in adults; young have bold, yellowish crossbands on a black background (Grenard, 1991; Conant and Collins, 1998). The voice of both males and females is a throaty, deep, bellowing roar (McIlhenny, 1935; Elliott, 1994; Conant and Collins, 1998). Elliott (1994) has made a recording of this penetrating roar available on a CD. Females may grunt like pigs when calling to their young (McIlhenny, 1935; Conant and Collins, 1998).
American alligators have been illustrated by numerous authors over the years; the list provided here is not exhaustive (Reese, 1912; McIlhenny, 1935; Neill, 1971; Guggisberg, 1972; Carr, 1973; Mount, 1975; Perrero, 1975; Smith and Smith, 1977; Behler and King, 1979; Toops, 1979; Martof et al., 1980; Smith and Brodie, 1982; Garrett and Barker, 1987; Webb et al., 1987; [Sievert] and Sievert, ; Dundee and Rossman, 1989; Hirschhorn, 1989; Lazell, 1989; Ross, 1989; Ross and Magnusson, 1989; Ashton and Ashton, 1991; Carmichael and Williams, 1991; Glasgow, 1991; Grenard, 1991; Mahony, 1991; Ross and Ernst, 1994; Palmer and Braswell, 1995; Lamar, 1997; Conant and Collins, 1998; Magnusson, 1998; Powell et al., 1998; Bartlett and Bartlett, 1999a, b; Behler, 1999; Zug et al., 2001).
Status: All the American alligators found in New York have been collected (Anderson and Habuda, 2001; Anonymous, 2001a, b; Beebe, 2001c; Heaton-Jones, 2001; Mikkelson and Mikkelson, 2001). They are not established in this state nor could they survive the cold winters, and the story of alligators dwelling in New York City sewers is simply a well-entrenched myth (Mikkelson and Mikkelson, 2001).
One of the alligators found in Union County, New Jersey, was collected; although there is no further word about the success of the 1933 great gator hunt started on the Passaic River in Essex County (Mikkelson and Mikkelson, 2001).
All A. mississippiensis from Virginia, West Virginia, Indiana, and California were collected with no further evidence of established populations (Bury and Luckenbach, 1978; Green and Pauley, 1987; Mitchell, 1994; Minton, 2001).
Palmer and Braswell (1995) provide little detail of nonindigenous A. mississippiensis in North Carolina, but suggest some individuals are "thriving." There is no evidence of reproduction.
There is a possibility that introduced American alligators in Oklahoma may establish populations in or near the southeastern corner of the state; thus interacting with indigenous populations in this region ([Sievert] and Sievert, ).
The A. mississippiensis populations in the Brownsville area, Cameron County, and the surrounding lower Rio Grande Valley are established but some authors suggest they could be nonindigenous (Conant, 1977; Conant and Collins, 1998). Since alligators were reported from the Brownsville region before the presumptive introductions took place (Baird, 1859), they are probably indigenous (Ross and Ernst, 1994). Indigenous populations may have simply been augmented by intentional introductions (Conant, 1977).
The A. mississippiensis in Boulder, Colorado, was collected (Livo et al., 1998). Only one of the American alligators was collected from the Colorado River, Mesa County, Colorado; the other was never recaptured, but there is no evidence of an established population (Livo et al., 1998).
The American alligators from Phoenix, Arizona, were collected (M. Demlong, personal communication 1997); however, Howland (1996) lists this species as "not well established" in Arizona.
References: (click for full references)
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This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.