Federal status“Threatened due to similarity ofappearance” to other crocodilian

speciesSize/age at maturity

6 ft./dependent on growth ratesTypical maximum size

males–13 to 14 feet,females–9 to 10 feet

Largest SRS alligator12’10” male that died in 1996

Weightvaries; adult males can be

500+ poundsLongevity

40 or more years in the wild,record 66 years in captivity

Home range sizeup to 2,000 acres for

adult malesHatchling size8 to 10 inchesClutch size20–60 eggs

Incubation periodapproximately 65 days

Teeth74 to 80

Name originAlligator is derived from the

Spanish el lagarto which means“the lizard”; mississippiensismeans “of or belonging to the

Mississippi”Ancestry

fossil records of crocodilianancestors, archosaurs, are

known from 225 million yearsago; archosaurs are thought to

have given rise to dinosaursand birds

This brochure was produced by the Savannah River EcologyLaboratory Environmental Outreach Program, in support ofPartners in Amphibian and Reptile Conservation (PARC;www.parcplace.org). Printing was sponsored by SREL(www.uga.edu/srel/), with additional program support from TheChristensen Fund and the Department of Energy. Text by DavidE. Scott, I. Lehr Brisbin, Jr., Travis C. Glenn, and William A.Hopkins. Photographs by David E. Scott(except as noted). Layout and design byLaura L. Janecek.

temperatures rose to such extremes? Byusing the combination of external andinternal temperature-sensitive transmitters,researchers learned that alligatorsresponded to thermal cues very rapidly,seeking cooler waters in coves, streamedges, or on stream bottomsonce their body temper-ature reached about91°F (33°C).

Like many wildlifespecies, alligatorsare vulnerable toenvironmental con-taminants. Becausealligators are top-levelcarnivores, they can bio-accumulate contaminantsin their tissues through the preyitems they ingest. Some environmentalcontaminants can be passed from femalealligators to eggs, potentially adverselyaffecting the health of developing offspring.Scientists at SREL are studying maternaltransfer of contaminants from females totheir offspring. On the SRS, alligators nestin a swamp downstream from a coal-burning power plant. The swamp iscontaminated with a variety of potentiallytoxic trace elements including arsenic,cadmium, and selenium (Se). Of theseelements, selenium is of great concernbecause it readily bioaccumulates andcauses developmental abnormalities whentransferred from females to developingembryos. Monitoring efforts in thecontaminated system revealed that adultfemale alligators accumulate Se andtransfer significant quantities to their eggs.Concentrations of Se in eggs and hatchlingscollected from the contaminated site are3-5 times higher than levels fromuncontaminated samples. Fortunately, theconcentrations of Se do not appear highenough to adversely affect developingoffspring; embryonic development, hatch-ing success, and hatchling size all appearnormal in clutches produced by femalealligators nesting in the contaminated area.

Alligators from the Par Pond population havealso been the subjects of contaminantstudies. Elevated levels of the radioactiveelement radiocesium (137Cs) occur in someportions of Par Pond as a result of reactoroperations. Cesium-137 mimics elemental

potassium when incorporatedinto plant and animal tissues;

in animals it tends toconcentrate in muscle

tissue. SREL studiesconcluded that al-though some indiv-iduals had elevatedlevels of 137Cs in their

bodies, there were nodetectable effects on

individual or populationhealth.

There is, however, reason for concern abouthuman consumption of alligators due to amuch more widely distributed environ-mental contaminant, mercury (Hg). Point-source pollution and atmospheric transportof this metal have resulted in many wildlifespecies having elevated Hg levels, even in“pristine” habitats. High Hg levels arecommon in wetland habitats and in top-levelpredators. Alligators are therefore primecandidates for exhibiting high Hgconcentrations. Mercury levels in the tissuesof SRS alligators, as well as those from othersoutheastern wetlands, have been analyzed.Although there are no national standards forHg concentrations in reptile meat, if thesame standards that are used for fish wereapplied to alligators (1 mg Hg/kg wet weightof tissue), then a high proportion ofalligators from the Everglades, other areasof Florida, and the SRS would be consideredunsafe for human consumption.

SREL scientists are also developing and usingmodern analytical and DNA techniques tolearn about alligators and solve environ-mental problems. For example, researchershave developed microsatellite DNA loci foralligators, which are the same type of geneticmarkers used for paternity analyses or

The American alligator, Alligator mississippiensis,occurs throughout most of the southeastern United States. Alligators

were once hunted primarily to produce leather products, which becamefashionable in the late 1800s. Untold numbers of animals were killed during

decades of unregulated hunting. Even after limited protection was put into effect insome areas in the mid-1900s, animals continued to be poached. As a result, alligator numbers

were dramatically reduced and in some regions it was feared that local populations would goextinct. Federal legislation in the 1970s and 1980s, including the Endangered Species Act of

1973 and amendments to the Lacey Act in 1981, ensured the alligator’s protection, and eventually its comeback. Todayalligator numbers are estimated in the millions and they are common throughout most of their historic range.

The story of the American alligator, both tragedy and success, is similarto that of many of its close kin, the crocodiles. Worldwide there are 23species of crocodilians; most were also hunted for food and skins,and by 1971 all crocodilians were endangered, threatened, or decliningin numbers. Habitat destruction in many countries exacerbated thedeclines. But a combination of legislation, effective law enforcement,dedicated conservationists, and innovative sustainable yield harvestingprograms reversed the decline for many species, despite continuinghabitat loss. Since the 1970s 16 of the 23 crocodilian species haveincreased in population size. However, some species, such as theChinese alligator, remain highly endangered in the wild.

The current federal protection status of the alligator remains as “threatened due to similarity of appearance” to endangeredcrocodiles (and products made from their skin). In some states alligators may be harvested using controlled hunts. Alligators arealso bred and raised in captivity for the production of meat and skins, but most of the half million farmed alligators are hatchedfrom eggs collected from the wild. The products from these tightly regulated wild harvests and alligator farms are now sold legally,providing important funds for the conservation of this species and its habitat.

HabitatAlligators live in fresh and brackish water habitats but will venture into saltwater. Alligators inhabit swamps, tidal marshes, creeks and rivers, canals, ponds,lakes, and reservoirs. In some areas alligators do something that only a fewspecies, such as humans and beavers, do—create wetland habitat. In marsh,sawgrass, and floodplain habitats gators sometimes create “gator holes,” whichprovide a refuge for many other animals during dry periods. Alligators createthe holes, which can be the size of a small backyard pool, using their snout,forefeet, and tail. Alligators are called a “keystone species” due to the stronginfluence they have on other species.

���������������

Alligator in a gator hole (photo by T.C. Glenn, SREL).

The American alligator and some crocodilespecies are prime examples of the concept of“sustainable use.” Sustainable use simply meansthat an organism is harvested at levels that canbe continued indefinitely. The specifics ofsustainable use programs vary among croco-dilian species, and among populations within aspecies in different parts of its geographic range.For example, the harvesting program foralligators in Florida differs from programs inLouisiana and other southeastern states; evenpopulations in different lakes within Florida aremanaged differently. The numbers of adultanimals that can be killed, as well as theproportions of eggs and hatchlings that can beremoved from the wild, are based on annualpopulation trends. The end result is that the legal,regulated harvest of various life stages does notharm the population, and gator and crocpopulations can thrive even as humans use themcommercially. In fact, many scientists believe thatsome crocodile species would be in far worseshape, and perhaps would have become extinct,if there were not a sustainable use managementprogram for those species. Carefully managedsustained-yield harvest programs provide directeconomic benefits to local people andcommunities, giving everyone an incentive toprotect both the species and its habitat.

human identification at crime scenes. Using these markers todetermine paternity in alligators led to the discovery that aboutone-third of all gator nests contain offspring from multiplefathers. In addition, although there are many 8-10 ft (2.4-3 m)male alligators in the gator population on the SRS, only the fewvery large males (11+ ft; 3.4+ m) sire offspring. Finally,microsatellites have been used in investigations of the effects ofcontaminants, leading to the discovery that the Hg and low-levels of radioactive contamination in some alligators on theSRS are not resulting in increased mutation rates relative togators from other populations. Continuing research will usethese genetic markers to make more discoveries about thebiology of alligators, solve other environmental problems, andeven produce a map of the alligator genome.

The recovery of alligator populations throughout the Southeast,combined with human population growth and encroachmenton wetland habitats, has increased the likelihood of gator-humaninteractions. Even so, the fact remains that the probability of analligator attacking aperson is extremelylow. The number ofalligators throughoutthe range at any givenpoint in time isprobably more thanthree million animals,yet on the average thereare fewer than 10attacks per year. Themajority of attacks haveoccurred in Florida,where there have been11 fatalities during a50-year period. Mostattacks occur either because alligators have lost their naturalfear of humans (due to being illegally fed by people and learningto associate humans with food) or because they are defendinga territory. Humans can do several things to minimize the riskof attack:� Do not feed alligators, thereby causing them to become

accustomed to humans.� Do not swim in areas (especially near heavily vegetated

shorelines) where large (>6 feet) alligators are present,particularly at night/dusk when they are feeding.

� Do not attempt to capture alligators—it is dangerous andagainst the law.

� Do not approach an alligator nest or hatchlings.

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The habitat preferences of alligators dependsomewhat on the size, age, and sex of thegator. Large adult male alligators generallyprefer deep, open water during the entireactive season. Large females also are foundin open water during the breeding season,but then move to marshes and lake edgesduring the nesting season and after younghave hatched. Smaller alligators (4-5 ft/1.2-1.5 m or less) typically occur in wetlandswith relatively dense vegetation, whichprovides both a hiding place and goodhabitat for prey items.

Reproduction, nesting, & hatchingThe time it takes for alligators to becomemature, and thus able to reproduce, variesfrom population to population. Repro-ductive maturity in alligators is primarilyrelated to body size, so the age at which anindividual can breed depends on how fastit grows throughout its life. Both males andfemales tend to mature at about 6 feet (1.8m) in length, but the size at which analligator may successfully breed is alsodependent upon social interactions amongmembers of the population. The courtshipand breeding season for alligators isgenerally from April through May, althoughthere are some reports of autumn mating.Breeding occurs in open water. Bodyposturing, snout rubbing, water slapping,and bellowing are all part of the courtshipprocess.

Range of the American alligator.After mating, females construct shorelinemound nests made from vegetation, leaflitter, and mud. In June and July femaleslay 20-60 eggs in the nest andcover them with additionalvegetation and debris.The temperature of thenest during themiddle third of theincubation perioddetermines the sexof the hatchlings.Constant incubationtemperatures below87.8oF (31oC) duringthis period produceonly females, temper-atures between 90.5 and91.4oF (32.5-33oC) produce onlymales, and temperatures above 93.2oF(34oC) produce a high proportion offemales. It generally takes a little morethan two months for the embryos todevelop and for hatchlings to emerge fromthe eggs. Eggs in alligator nests are oftenpreyed upon by raccoons, opossums,skunks, pigs, and other nest predators.For example, in Florida it is considered“normal” if only 50% of the eggs escapepredation and hatch. At hatching time thebabies make a call that attracts the female.She uncovers the hatchlings in the nest bydigging with her front feet and snout andmay carry hatchlings in her mouth fromthe nest to the water’s edge.

Most reptile species do very little“parenting,” especially after the eggs havehatched. In contrast, femalealligators will protect babiesat all stages: eggs in thenest, hatchlings, and babiesup to three years old.Hatchling gators generallystay together in a “pod” for1-3 years, and make a call(presumably a distress call)to which females respond.Nonetheless, many hatch-lings are preyed upon by a

wide variety of animals, including largewading birds, snakes, bass, and evenbullfrogs.

Feeding habitsThe diet of alligators is

quite varied, and isdependent upon thesize of the gator. Allgators, regardless ofsize, are primarilycarnivores, althoughsome plant material

may incidentally beingested. Hatchlings

and young alligators eatinsects, crayfish, snails and

other invertebrates, small fish,and amphibians. At 5-6 ft long (1.5-

1.8 m) alligators begin to feed more onlarge fish, turtles, snakes, waterfowl andwading birds, and small mammals. Inaddition to keen eyesight, hundreds ofspecialized pressure sensors on the snoutsof gators help them locate prey in the water;these bumps are sensitive enough to detectripples from a single drop of water. Becausealligators are “cold blooded” their feedingactivity is dependent on water temper-ature—gators will usually stop feeding ifwater temperatures are below approxi-mately 70oF (21oC). Thus, alligatorsgenerally feed from late March/early Aprilthrough October.

Growth & body sizeGrowth rates in young alligators vary from4-14” (10-36 cm) per year, depending on

The American alligator (top) and Americancrocodile (right) are native to the U.S. The spectacledcaiman (lower left) is established in parts of southFlorida. Species are distinguished primarily bylocation (range and habitat), head shape, and teeth.

An alligator exhibiting “icing” behavoir.

reproductive synchronization with femalesthat remained in the cooler parts of thereservoir and entered typical winterdormancy. Researchers speculated that thealtered male activity cycle may have causeda change in the timing of male repro-duction, and made males incapable ofbreeding by the time females became activeand ready to breed in the spring. Indeed,the early gator population at Par Pond hadan unusually high proportion of adults(64%) and few juveniles, the pattern onemight expect if females were not nestingand producing young. However, the samepattern might occur if males are morelikely than females to colonize new aquatichabitats, resulting in a male-biased sexratio with few adult females available forbreeding. In 1974 there were 3.2 malealligators for every female, and only anestimated 15 females in all of Par Pond.Multiple possible causes for a singleobserved pattern illustrates why sciencecan be so challenging!

By the mid-1980s the Par Pond alligatorpopulation had nearly doubled from 1974estimates, to a total of almost 200 adultsand juveniles (42%), with 24 adult females.

SREL scientists foundthemselves in a uniqueposition in 1991, whenPar Pond was loweredapproximately 18 ft (5.5m) while repairs weremade to the dam.Radiotracking studiesduring the 3-year periodof low water levelshowed that breedingfemales remained in thelowered reservoir andcontinued to nest successfully. However,survival of young from these nests wasextremely low because the draw-downhad denuded the reservoir shoreline ofmuch of the emergent aquatic vegetationthat newly hatched alligators need forprotection from predators. Some adultalligators, primarily males, moved fromPar Pond to nearby bodies of water. L-Lake, a new reservoir constructed in late1985, is approximately 4 miles (6.4 km)from Par Pond. By 1988 alligators hadnot colonized the reservoir, but in the1990s alligators began to take upresidence in the new lake, although nonewere identified as known Par Pondanimals. Researchers continue to studythe colonization of L-Lake by alligators,which had reached a population size ofseveral dozen (mostly adults) by the late1990s.

SREL biologists have also used thetechnique of radiotelemetry to learnabout alligator physiology. Radio-transmitters can be designed so that thepulse rate of the radio signal isdependent on temperature, simplymeaning that the sound a biologisthears when tracking the animal isslower when cold and faster whenwarm. In the case of a large alligator,researchers attached one trans-mitter on a collar to the outside ofthe animal, and inserted onetransmitter into the stomach, so thatboth the environmental temperature

and body temperature were determined.Using these methods researchers studiedthe body temperature and behaviorrelationships of larger alligators as theyfaced cold weather in unheated reservoirs.

Similar techniques were used in otherstudies of the effects of thermal effluentfrom reactors. In addition to coolingreservoirs, three SRS streams receivedthermal effluent during periods of reactoroperation. In the 1980s SREL researchersexamined how hot water plumes in SRSstreams affected alligators. At the time,alligators were still a federally listedendangered species in inland SouthCarolina, and the impact of hot water onalligators was of concern to the Departmentof Energy. Researchers had alreadydetermined that the critical thermalmaximum (CTM), or the temperature atwhich alligators would overheat and die,was 100°F (38°C). Temperatures in partsof some SRS streams exceeded 104°F(40°C) when reactors were operating. Howdid alligators respond when water

����������������������

temperature, food resources of the habitat, and the animal’s sex, size,and age. For example, juvenile alligators in some South Carolinapopulations average 7.5” (19 cm) of growth per year, while those inLouisiana may grow 12” (30.5 cm) per year. Because maturity is relatedto body size, this means that alligators in Louisiana may reach maturityearlier than those in South Carolina. As alligators get larger their growthrate slows, and once an alligator becomes reproductively mature itsgrowth rate drops dramatically. Male alligators grow faster and largerthan females. Females can attain approximately 9 ft (2.7 m) in lengthand 200+ lbs (91 kg). Males can grow to 13+ ft (4 m) and 500+ lbs(227 kg). The record alligator, taken on Marsh Island, Louisiana, wasreported to be 19’2” long.

Interesting behaviorsFor an animal with a maximum brain mass of less than ½ ounce (~10.5grams), alligators demonstrate some interesting behaviors.� In the temperate portions of their range, alligators construct dens

(a cave-like structure in the bank of the waterway) where theyremain dormant during winter months. Gators also exhibit “icingbehavior” in response to extreme cold. Before a pond freezes, anadult will move to shallow water, place its nostrils (on the tip ofthe snout) out of the water, and let its snout become frozen intothe ice. Hatchlings and juveniles may not be as successful at this,which may explain (in part) the limits to the range of the alligator.

� Humans can hear a wide variety of the sounds that alligators use

to communicate, fromcoughing and hissing todistress yelps, hatchingcalls, and bellowing. Inaddition, alligators areone of many species ofanimals that commun-icate using sounds thatwe cannot hear.Humans hear sound inthe range of 20-20,000Hz (hertz; cycles persecond), and somealligator vocalizationsare below 20 Hz, in the infrasound range. Low frequency soundcan travel very long distances.

� Researchers who have used radiotransmitters to track alligatorshave learned that they have large home range sizes, with malesusing a larger area than females. Males move the most and havetheir largest home ranges during the breeding season, and femalesmove the least and have their smallest ranges during the nestingseason. Alligator home range size depends on many factors,including the location and type of habitat, but an adult male alligatormay have a home range of more than 1,000 acres.

� Unique among reptiles, crocodilians have been observed bringingfood to their young.

The University of Georgia’s Savannah River Ecology Laboratory (SREL)began conducting ecological studies on the newly created SavannahRiver Site (SRS) on the upper Coastal Plain of South Carolina in 1951.Studies of the American alligator on the SRS have increased ourknowledge about its basic ecology and provided insights on the effectsof industrial facilities on alligators. SREL’s ongoing research, incollaboration with researchers from around the world, continues tolead to new discoveries about alligators and other crocodilians.

The SREL program of alligator research began in the late 1960s whennuclear production reactors were periodically discharging heatedeffluents into cooling reservoirs and streams on the SRS. The heatedwaters created unique gradients of water temperature never beforeexperienced by alligators. As one example of a “thermal effect,” alligatorsthat inhabited the warm portions of the 2,840 acre (1,150 hectare)Par Pond reservoir were noted to bask less frequently, especially duringcooler months, than gators in normal-temperature water. Research overthe next decade documented the seasonal use of heated waters,particularly by larger males that moved into the warm waters andremained active during the winter months of the year. The prolongedactive season of these larger male alligators seemed to put them out of

Hatchling gator hitching a ride on Mom

.

The habitat preferences of alligators dependsomewhat on the size, age, and sex of thegator. Large adult male alligators generallyprefer deep, open water during the entireactive season. Large females also are foundin open water during the breeding season,but then move to marshes and lake edgesduring the nesting season and after younghave hatched. Smaller alligators (4-5 ft/1.2-1.5 m or less) typically occur in wetlandswith relatively dense vegetation, whichprovides both a hiding place and goodhabitat for prey items.

Reproduction, nesting, & hatchingThe time it takes for alligators to becomemature, and thus able to reproduce, variesfrom population to population. Repro-ductive maturity in alligators is primarilyrelated to body size, so the age at which anindividual can breed depends on how fastit grows throughout its life. Both males andfemales tend to mature at about 6 feet (1.8m) in length, but the size at which analligator may successfully breed is alsodependent upon social interactions amongmembers of the population. The courtshipand breeding season for alligators isgenerally from April through May, althoughthere are some reports of autumn mating.Breeding occurs in open water. Bodyposturing, snout rubbing, water slapping,and bellowing are all part of the courtshipprocess.

Range of the American alligator.After mating, females construct shorelinemound nests made from vegetation, leaflitter, and mud. In June and July femaleslay 20-60 eggs in the nest andcover them with additionalvegetation and debris.The temperature of thenest during themiddle third of theincubation perioddetermines the sexof the hatchlings.Constant incubationtemperatures below87.8oF (31oC) duringthis period produceonly females, temper-atures between 90.5 and91.4oF (32.5-33oC) produce onlymales, and temperatures above 93.2oF(34oC) produce a high proportion offemales. It generally takes a little morethan two months for the embryos todevelop and for hatchlings to emerge fromthe eggs. Eggs in alligator nests are oftenpreyed upon by raccoons, opossums,skunks, pigs, and other nest predators.For example, in Florida it is considered“normal” if only 50% of the eggs escapepredation and hatch. At hatching time thebabies make a call that attracts the female.She uncovers the hatchlings in the nest bydigging with her front feet and snout andmay carry hatchlings in her mouth fromthe nest to the water’s edge.

Most reptile species do very little“parenting,” especially after the eggs havehatched. In contrast, femalealligators will protect babiesat all stages: eggs in thenest, hatchlings, and babiesup to three years old.Hatchling gators generallystay together in a “pod” for1-3 years, and make a call(presumably a distress call)to which females respond.Nonetheless, many hatch-lings are preyed upon by a

wide variety of animals, including largewading birds, snakes, bass, and evenbullfrogs.

Feeding habitsThe diet of alligators is

quite varied, and isdependent upon thesize of the gator. Allgators, regardless ofsize, are primarilycarnivores, althoughsome plant material

may incidentally beingested. Hatchlings

and young alligators eatinsects, crayfish, snails and

other invertebrates, small fish,and amphibians. At 5-6 ft long (1.5-

1.8 m) alligators begin to feed more onlarge fish, turtles, snakes, waterfowl andwading birds, and small mammals. Inaddition to keen eyesight, hundreds ofspecialized pressure sensors on the snoutsof gators help them locate prey in the water;these bumps are sensitive enough to detectripples from a single drop of water. Becausealligators are “cold blooded” their feedingactivity is dependent on water temper-ature—gators will usually stop feeding ifwater temperatures are below approxi-mately 70oF (21oC). Thus, alligatorsgenerally feed from late March/early Aprilthrough October.

Growth & body sizeGrowth rates in young alligators vary from4-14” (10-36 cm) per year, depending on

The American alligator (top) and Americancrocodile (right) are native to the U.S. The spectacledcaiman (lower left) is established in parts of southFlorida. Species are distinguished primarily bylocation (range and habitat), head shape, and teeth.

An alligator exhibiting “icing” behavoir.

reproductive synchronization with femalesthat remained in the cooler parts of thereservoir and entered typical winterdormancy. Researchers speculated that thealtered male activity cycle may have causeda change in the timing of male repro-duction, and made males incapable ofbreeding by the time females became activeand ready to breed in the spring. Indeed,the early gator population at Par Pond hadan unusually high proportion of adults(64%) and few juveniles, the pattern onemight expect if females were not nestingand producing young. However, the samepattern might occur if males are morelikely than females to colonize new aquatichabitats, resulting in a male-biased sexratio with few adult females available forbreeding. In 1974 there were 3.2 malealligators for every female, and only anestimated 15 females in all of Par Pond.Multiple possible causes for a singleobserved pattern illustrates why sciencecan be so challenging!

By the mid-1980s the Par Pond alligatorpopulation had nearly doubled from 1974estimates, to a total of almost 200 adultsand juveniles (42%), with 24 adult females.

SREL scientists foundthemselves in a uniqueposition in 1991, whenPar Pond was loweredapproximately 18 ft (5.5m) while repairs weremade to the dam.Radiotracking studiesduring the 3-year periodof low water levelshowed that breedingfemales remained in thelowered reservoir andcontinued to nest successfully. However,survival of young from these nests wasextremely low because the draw-downhad denuded the reservoir shoreline ofmuch of the emergent aquatic vegetationthat newly hatched alligators need forprotection from predators. Some adultalligators, primarily males, moved fromPar Pond to nearby bodies of water. L-Lake, a new reservoir constructed in late1985, is approximately 4 miles (6.4 km)from Par Pond. By 1988 alligators hadnot colonized the reservoir, but in the1990s alligators began to take upresidence in the new lake, although nonewere identified as known Par Pondanimals. Researchers continue to studythe colonization of L-Lake by alligators,which had reached a population size ofseveral dozen (mostly adults) by the late1990s.

SREL biologists have also used thetechnique of radiotelemetry to learnabout alligator physiology. Radio-transmitters can be designed so that thepulse rate of the radio signal isdependent on temperature, simplymeaning that the sound a biologisthears when tracking the animal isslower when cold and faster whenwarm. In the case of a large alligator,researchers attached one trans-mitter on a collar to the outside ofthe animal, and inserted onetransmitter into the stomach, so thatboth the environmental temperature

and body temperature were determined.Using these methods researchers studiedthe body temperature and behaviorrelationships of larger alligators as theyfaced cold weather in unheated reservoirs.

Similar techniques were used in otherstudies of the effects of thermal effluentfrom reactors. In addition to coolingreservoirs, three SRS streams receivedthermal effluent during periods of reactoroperation. In the 1980s SREL researchersexamined how hot water plumes in SRSstreams affected alligators. At the time,alligators were still a federally listedendangered species in inland SouthCarolina, and the impact of hot water onalligators was of concern to the Departmentof Energy. Researchers had alreadydetermined that the critical thermalmaximum (CTM), or the temperature atwhich alligators would overheat and die,was 100°F (38°C). Temperatures in partsof some SRS streams exceeded 104°F(40°C) when reactors were operating. Howdid alligators respond when water

����������������������

temperature, food resources of the habitat, and the animal’s sex, size,and age. For example, juvenile alligators in some South Carolinapopulations average 7.5” (19 cm) of growth per year, while those inLouisiana may grow 12” (30.5 cm) per year. Because maturity is relatedto body size, this means that alligators in Louisiana may reach maturityearlier than those in South Carolina. As alligators get larger their growthrate slows, and once an alligator becomes reproductively mature itsgrowth rate drops dramatically. Male alligators grow faster and largerthan females. Females can attain approximately 9 ft (2.7 m) in lengthand 200+ lbs (91 kg). Males can grow to 13+ ft (4 m) and 500+ lbs(227 kg). The record alligator, taken on Marsh Island, Louisiana, wasreported to be 19’2” long.

Interesting behaviorsFor an animal with a maximum brain mass of less than ½ ounce (~10.5grams), alligators demonstrate some interesting behaviors.� In the temperate portions of their range, alligators construct dens

(a cave-like structure in the bank of the waterway) where theyremain dormant during winter months. Gators also exhibit “icingbehavior” in response to extreme cold. Before a pond freezes, anadult will move to shallow water, place its nostrils (on the tip ofthe snout) out of the water, and let its snout become frozen intothe ice. Hatchlings and juveniles may not be as successful at this,which may explain (in part) the limits to the range of the alligator.

� Humans can hear a wide variety of the sounds that alligators use

to communicate, fromcoughing and hissing todistress yelps, hatchingcalls, and bellowing. Inaddition, alligators areone of many species ofanimals that commun-icate using sounds thatwe cannot hear.Humans hear sound inthe range of 20-20,000Hz (hertz; cycles persecond), and somealligator vocalizationsare below 20 Hz, in the infrasound range. Low frequency soundcan travel very long distances.

� Researchers who have used radiotransmitters to track alligatorshave learned that they have large home range sizes, with malesusing a larger area than females. Males move the most and havetheir largest home ranges during the breeding season, and femalesmove the least and have their smallest ranges during the nestingseason. Alligator home range size depends on many factors,including the location and type of habitat, but an adult male alligatormay have a home range of more than 1,000 acres.

� Unique among reptiles, crocodilians have been observed bringingfood to their young.

The University of Georgia’s Savannah River Ecology Laboratory (SREL)began conducting ecological studies on the newly created SavannahRiver Site (SRS) on the upper Coastal Plain of South Carolina in 1951.Studies of the American alligator on the SRS have increased ourknowledge about its basic ecology and provided insights on the effectsof industrial facilities on alligators. SREL’s ongoing research, incollaboration with researchers from around the world, continues tolead to new discoveries about alligators and other crocodilians.

The SREL program of alligator research began in the late 1960s whennuclear production reactors were periodically discharging heatedeffluents into cooling reservoirs and streams on the SRS. The heatedwaters created unique gradients of water temperature never beforeexperienced by alligators. As one example of a “thermal effect,” alligatorsthat inhabited the warm portions of the 2,840 acre (1,150 hectare)Par Pond reservoir were noted to bask less frequently, especially duringcooler months, than gators in normal-temperature water. Research overthe next decade documented the seasonal use of heated waters,particularly by larger males that moved into the warm waters andremained active during the winter months of the year. The prolongedactive season of these larger male alligators seemed to put them out of

Hatchling gator hitching a ride on Mom

.

The habitat preferences of alligators dependsomewhat on the size, age, and sex of thegator. Large adult male alligators generallyprefer deep, open water during the entireactive season. Large females also are foundin open water during the breeding season,but then move to marshes and lake edgesduring the nesting season and after younghave hatched. Smaller alligators (4-5 ft/1.2-1.5 m or less) typically occur in wetlandswith relatively dense vegetation, whichprovides both a hiding place and goodhabitat for prey items.

Reproduction, nesting, & hatchingThe time it takes for alligators to becomemature, and thus able to reproduce, variesfrom population to population. Repro-ductive maturity in alligators is primarilyrelated to body size, so the age at which anindividual can breed depends on how fastit grows throughout its life. Both males andfemales tend to mature at about 6 feet (1.8m) in length, but the size at which analligator may successfully breed is alsodependent upon social interactions amongmembers of the population. The courtshipand breeding season for alligators isgenerally from April through May, althoughthere are some reports of autumn mating.Breeding occurs in open water. Bodyposturing, snout rubbing, water slapping,and bellowing are all part of the courtshipprocess.

Range of the American alligator.After mating, females construct shorelinemound nests made from vegetation, leaflitter, and mud. In June and July femaleslay 20-60 eggs in the nest andcover them with additionalvegetation and debris.The temperature of thenest during themiddle third of theincubation perioddetermines the sexof the hatchlings.Constant incubationtemperatures below87.8oF (31oC) duringthis period produceonly females, temper-atures between 90.5 and91.4oF (32.5-33oC) produce onlymales, and temperatures above 93.2oF(34oC) produce a high proportion offemales. It generally takes a little morethan two months for the embryos todevelop and for hatchlings to emerge fromthe eggs. Eggs in alligator nests are oftenpreyed upon by raccoons, opossums,skunks, pigs, and other nest predators.For example, in Florida it is considered“normal” if only 50% of the eggs escapepredation and hatch. At hatching time thebabies make a call that attracts the female.She uncovers the hatchlings in the nest bydigging with her front feet and snout andmay carry hatchlings in her mouth fromthe nest to the water’s edge.

Most reptile species do very little“parenting,” especially after the eggs havehatched. In contrast, femalealligators will protect babiesat all stages: eggs in thenest, hatchlings, and babiesup to three years old.Hatchling gators generallystay together in a “pod” for1-3 years, and make a call(presumably a distress call)to which females respond.Nonetheless, many hatch-lings are preyed upon by a

wide variety of animals, including largewading birds, snakes, bass, and evenbullfrogs.

Feeding habitsThe diet of alligators is

quite varied, and isdependent upon thesize of the gator. Allgators, regardless ofsize, are primarilycarnivores, althoughsome plant material

may incidentally beingested. Hatchlings

and young alligators eatinsects, crayfish, snails and

other invertebrates, small fish,and amphibians. At 5-6 ft long (1.5-

1.8 m) alligators begin to feed more onlarge fish, turtles, snakes, waterfowl andwading birds, and small mammals. Inaddition to keen eyesight, hundreds ofspecialized pressure sensors on the snoutsof gators help them locate prey in the water;these bumps are sensitive enough to detectripples from a single drop of water. Becausealligators are “cold blooded” their feedingactivity is dependent on water temper-ature—gators will usually stop feeding ifwater temperatures are below approxi-mately 70oF (21oC). Thus, alligatorsgenerally feed from late March/early Aprilthrough October.

Growth & body sizeGrowth rates in young alligators vary from4-14” (10-36 cm) per year, depending on

The American alligator (top) and Americancrocodile (right) are native to the U.S. The spectacledcaiman (lower left) is established in parts of southFlorida. Species are distinguished primarily bylocation (range and habitat), head shape, and teeth.

An alligator exhibiting “icing” behavoir.

reproductive synchronization with femalesthat remained in the cooler parts of thereservoir and entered typical winterdormancy. Researchers speculated that thealtered male activity cycle may have causeda change in the timing of male repro-duction, and made males incapable ofbreeding by the time females became activeand ready to breed in the spring. Indeed,the early gator population at Par Pond hadan unusually high proportion of adults(64%) and few juveniles, the pattern onemight expect if females were not nestingand producing young. However, the samepattern might occur if males are morelikely than females to colonize new aquatichabitats, resulting in a male-biased sexratio with few adult females available forbreeding. In 1974 there were 3.2 malealligators for every female, and only anestimated 15 females in all of Par Pond.Multiple possible causes for a singleobserved pattern illustrates why sciencecan be so challenging!

By the mid-1980s the Par Pond alligatorpopulation had nearly doubled from 1974estimates, to a total of almost 200 adultsand juveniles (42%), with 24 adult females.

SREL scientists foundthemselves in a uniqueposition in 1991, whenPar Pond was loweredapproximately 18 ft (5.5m) while repairs weremade to the dam.Radiotracking studiesduring the 3-year periodof low water levelshowed that breedingfemales remained in thelowered reservoir andcontinued to nest successfully. However,survival of young from these nests wasextremely low because the draw-downhad denuded the reservoir shoreline ofmuch of the emergent aquatic vegetationthat newly hatched alligators need forprotection from predators. Some adultalligators, primarily males, moved fromPar Pond to nearby bodies of water. L-Lake, a new reservoir constructed in late1985, is approximately 4 miles (6.4 km)from Par Pond. By 1988 alligators hadnot colonized the reservoir, but in the1990s alligators began to take upresidence in the new lake, although nonewere identified as known Par Pondanimals. Researchers continue to studythe colonization of L-Lake by alligators,which had reached a population size ofseveral dozen (mostly adults) by the late1990s.

SREL biologists have also used thetechnique of radiotelemetry to learnabout alligator physiology. Radio-transmitters can be designed so that thepulse rate of the radio signal isdependent on temperature, simplymeaning that the sound a biologisthears when tracking the animal isslower when cold and faster whenwarm. In the case of a large alligator,researchers attached one trans-mitter on a collar to the outside ofthe animal, and inserted onetransmitter into the stomach, so thatboth the environmental temperature

and body temperature were determined.Using these methods researchers studiedthe body temperature and behaviorrelationships of larger alligators as theyfaced cold weather in unheated reservoirs.

Similar techniques were used in otherstudies of the effects of thermal effluentfrom reactors. In addition to coolingreservoirs, three SRS streams receivedthermal effluent during periods of reactoroperation. In the 1980s SREL researchersexamined how hot water plumes in SRSstreams affected alligators. At the time,alligators were still a federally listedendangered species in inland SouthCarolina, and the impact of hot water onalligators was of concern to the Departmentof Energy. Researchers had alreadydetermined that the critical thermalmaximum (CTM), or the temperature atwhich alligators would overheat and die,was 100°F (38°C). Temperatures in partsof some SRS streams exceeded 104°F(40°C) when reactors were operating. Howdid alligators respond when water

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temperature, food resources of the habitat, and the animal’s sex, size,and age. For example, juvenile alligators in some South Carolinapopulations average 7.5” (19 cm) of growth per year, while those inLouisiana may grow 12” (30.5 cm) per year. Because maturity is relatedto body size, this means that alligators in Louisiana may reach maturityearlier than those in South Carolina. As alligators get larger their growthrate slows, and once an alligator becomes reproductively mature itsgrowth rate drops dramatically. Male alligators grow faster and largerthan females. Females can attain approximately 9 ft (2.7 m) in lengthand 200+ lbs (91 kg). Males can grow to 13+ ft (4 m) and 500+ lbs(227 kg). The record alligator, taken on Marsh Island, Louisiana, wasreported to be 19’2” long.

Interesting behaviorsFor an animal with a maximum brain mass of less than ½ ounce (~10.5grams), alligators demonstrate some interesting behaviors.� In the temperate portions of their range, alligators construct dens

(a cave-like structure in the bank of the waterway) where theyremain dormant during winter months. Gators also exhibit “icingbehavior” in response to extreme cold. Before a pond freezes, anadult will move to shallow water, place its nostrils (on the tip ofthe snout) out of the water, and let its snout become frozen intothe ice. Hatchlings and juveniles may not be as successful at this,which may explain (in part) the limits to the range of the alligator.

� Humans can hear a wide variety of the sounds that alligators use

to communicate, fromcoughing and hissing todistress yelps, hatchingcalls, and bellowing. Inaddition, alligators areone of many species ofanimals that commun-icate using sounds thatwe cannot hear.Humans hear sound inthe range of 20-20,000Hz (hertz; cycles persecond), and somealligator vocalizationsare below 20 Hz, in the infrasound range. Low frequency soundcan travel very long distances.

� Researchers who have used radiotransmitters to track alligatorshave learned that they have large home range sizes, with malesusing a larger area than females. Males move the most and havetheir largest home ranges during the breeding season, and femalesmove the least and have their smallest ranges during the nestingseason. Alligator home range size depends on many factors,including the location and type of habitat, but an adult male alligatormay have a home range of more than 1,000 acres.

� Unique among reptiles, crocodilians have been observed bringingfood to their young.

The University of Georgia’s Savannah River Ecology Laboratory (SREL)began conducting ecological studies on the newly created SavannahRiver Site (SRS) on the upper Coastal Plain of South Carolina in 1951.Studies of the American alligator on the SRS have increased ourknowledge about its basic ecology and provided insights on the effectsof industrial facilities on alligators. SREL’s ongoing research, incollaboration with researchers from around the world, continues tolead to new discoveries about alligators and other crocodilians.

The SREL program of alligator research began in the late 1960s whennuclear production reactors were periodically discharging heatedeffluents into cooling reservoirs and streams on the SRS. The heatedwaters created unique gradients of water temperature never beforeexperienced by alligators. As one example of a “thermal effect,” alligatorsthat inhabited the warm portions of the 2,840 acre (1,150 hectare)Par Pond reservoir were noted to bask less frequently, especially duringcooler months, than gators in normal-temperature water. Research overthe next decade documented the seasonal use of heated waters,particularly by larger males that moved into the warm waters andremained active during the winter months of the year. The prolongedactive season of these larger male alligators seemed to put them out of

Hatchling gator hitching a ride on Mom

.

Federal status“Threatened due to similarity ofappearance” to other crocodilian

speciesSize/age at maturity

6 ft./dependent on growth ratesTypical maximum size

males–13 to 14 feet,females–9 to 10 feet

Largest SRS alligator12’10” male that died in 1996

Weightvaries; adult males can be

500+ poundsLongevity

40 or more years in the wild,record 66 years in captivity

Home range sizeup to 2,000 acres for

adult malesHatchling size8 to 10 inchesClutch size20–60 eggs

Incubation periodapproximately 65 days

Teeth74 to 80

Name originAlligator is derived from the

Spanish el lagarto which means“the lizard”; mississippiensismeans “of or belonging to the

Mississippi”Ancestry

fossil records of crocodilianancestors, archosaurs, are

known from 225 million yearsago; archosaurs are thought to

have given rise to dinosaursand birds

This brochure was produced by the Savannah River EcologyLaboratory Environmental Outreach Program, in support ofPartners in Amphibian and Reptile Conservation (PARC;www.parcplace.org). Printing was sponsored by SREL(www.uga.edu/srel/), with additional program support from TheChristensen Fund and the Department of Energy. Text by DavidE. Scott, I. Lehr Brisbin, Jr., Travis C. Glenn, and William A.Hopkins. Photographs by David E. Scott(except as noted). Layout and design byLaura L. Janecek.

temperatures rose to such extremes? Byusing the combination of external andinternal temperature-sensitive transmitters,researchers learned that alligatorsresponded to thermal cues very rapidly,seeking cooler waters in coves, streamedges, or on stream bottomsonce their body temper-ature reached about91°F (33°C).

Like many wildlifespecies, alligatorsare vulnerable toenvironmental con-taminants. Becausealligators are top-levelcarnivores, they can bio-accumulate contaminantsin their tissues through the preyitems they ingest. Some environmentalcontaminants can be passed from femalealligators to eggs, potentially adverselyaffecting the health of developing offspring.Scientists at SREL are studying maternaltransfer of contaminants from females totheir offspring. On the SRS, alligators nestin a swamp downstream from a coal-burning power plant. The swamp iscontaminated with a variety of potentiallytoxic trace elements including arsenic,cadmium, and selenium (Se). Of theseelements, selenium is of great concernbecause it readily bioaccumulates andcauses developmental abnormalities whentransferred from females to developingembryos. Monitoring efforts in thecontaminated system revealed that adultfemale alligators accumulate Se andtransfer significant quantities to their eggs.Concentrations of Se in eggs and hatchlingscollected from the contaminated site are3-5 times higher than levels fromuncontaminated samples. Fortunately, theconcentrations of Se do not appear highenough to adversely affect developingoffspring; embryonic development, hatch-ing success, and hatchling size all appearnormal in clutches produced by femalealligators nesting in the contaminated area.

Alligators from the Par Pond population havealso been the subjects of contaminantstudies. Elevated levels of the radioactiveelement radiocesium (137Cs) occur in someportions of Par Pond as a result of reactoroperations. Cesium-137 mimics elemental

potassium when incorporatedinto plant and animal tissues;

in animals it tends toconcentrate in muscle

tissue. SREL studiesconcluded that al-though some indiv-iduals had elevatedlevels of 137Cs in their

bodies, there were nodetectable effects on

individual or populationhealth.

There is, however, reason for concern abouthuman consumption of alligators due to amuch more widely distributed environ-mental contaminant, mercury (Hg). Point-source pollution and atmospheric transportof this metal have resulted in many wildlifespecies having elevated Hg levels, even in“pristine” habitats. High Hg levels arecommon in wetland habitats and in top-levelpredators. Alligators are therefore primecandidates for exhibiting high Hgconcentrations. Mercury levels in the tissuesof SRS alligators, as well as those from othersoutheastern wetlands, have been analyzed.Although there are no national standards forHg concentrations in reptile meat, if thesame standards that are used for fish wereapplied to alligators (1 mg Hg/kg wet weightof tissue), then a high proportion ofalligators from the Everglades, other areasof Florida, and the SRS would be consideredunsafe for human consumption.

SREL scientists are also developing and usingmodern analytical and DNA techniques tolearn about alligators and solve environ-mental problems. For example, researchershave developed microsatellite DNA loci foralligators, which are the same type of geneticmarkers used for paternity analyses or

The American alligator, Alligator mississippiensis,occurs throughout most of the southeastern United States. Alligators

were once hunted primarily to produce leather products, which becamefashionable in the late 1800s. Untold numbers of animals were killed during

decades of unregulated hunting. Even after limited protection was put into effect insome areas in the mid-1900s, animals continued to be poached. As a result, alligator numbers

were dramatically reduced and in some regions it was feared that local populations would goextinct. Federal legislation in the 1970s and 1980s, including the Endangered Species Act of

1973 and amendments to the Lacey Act in 1981, ensured the alligator’s protection, and eventually its comeback. Todayalligator numbers are estimated in the millions and they are common throughout most of their historic range.

The story of the American alligator, both tragedy and success, is similarto that of many of its close kin, the crocodiles. Worldwide there are 23species of crocodilians; most were also hunted for food and skins,and by 1971 all crocodilians were endangered, threatened, or decliningin numbers. Habitat destruction in many countries exacerbated thedeclines. But a combination of legislation, effective law enforcement,dedicated conservationists, and innovative sustainable yield harvestingprograms reversed the decline for many species, despite continuinghabitat loss. Since the 1970s 16 of the 23 crocodilian species haveincreased in population size. However, some species, such as theChinese alligator, remain highly endangered in the wild.

The current federal protection status of the alligator remains as “threatened due to similarity of appearance” to endangeredcrocodiles (and products made from their skin). In some states alligators may be harvested using controlled hunts. Alligators arealso bred and raised in captivity for the production of meat and skins, but most of the half million farmed alligators are hatchedfrom eggs collected from the wild. The products from these tightly regulated wild harvests and alligator farms are now sold legally,providing important funds for the conservation of this species and its habitat.

HabitatAlligators live in fresh and brackish water habitats but will venture into saltwater. Alligators inhabit swamps, tidal marshes, creeks and rivers, canals, ponds,lakes, and reservoirs. In some areas alligators do something that only a fewspecies, such as humans and beavers, do—create wetland habitat. In marsh,sawgrass, and floodplain habitats gators sometimes create “gator holes,” whichprovide a refuge for many other animals during dry periods. Alligators createthe holes, which can be the size of a small backyard pool, using their snout,forefeet, and tail. Alligators are called a “keystone species” due to the stronginfluence they have on other species.

���������������

Alligator in a gator hole (photo by T.C. Glenn, SREL).

The American alligator and some crocodilespecies are prime examples of the concept of“sustainable use.” Sustainable use simply meansthat an organism is harvested at levels that canbe continued indefinitely. The specifics ofsustainable use programs vary among croco-dilian species, and among populations within aspecies in different parts of its geographic range.For example, the harvesting program foralligators in Florida differs from programs inLouisiana and other southeastern states; evenpopulations in different lakes within Florida aremanaged differently. The numbers of adultanimals that can be killed, as well as theproportions of eggs and hatchlings that can beremoved from the wild, are based on annualpopulation trends. The end result is that the legal,regulated harvest of various life stages does notharm the population, and gator and crocpopulations can thrive even as humans use themcommercially. In fact, many scientists believe thatsome crocodile species would be in far worseshape, and perhaps would have become extinct,if there were not a sustainable use managementprogram for those species. Carefully managedsustained-yield harvest programs provide directeconomic benefits to local people andcommunities, giving everyone an incentive toprotect both the species and its habitat.

human identification at crime scenes. Using these markers todetermine paternity in alligators led to the discovery that aboutone-third of all gator nests contain offspring from multiplefathers. In addition, although there are many 8-10 ft (2.4-3 m)male alligators in the gator population on the SRS, only the fewvery large males (11+ ft; 3.4+ m) sire offspring. Finally,microsatellites have been used in investigations of the effects ofcontaminants, leading to the discovery that the Hg and low-levels of radioactive contamination in some alligators on theSRS are not resulting in increased mutation rates relative togators from other populations. Continuing research will usethese genetic markers to make more discoveries about thebiology of alligators, solve other environmental problems, andeven produce a map of the alligator genome.

The recovery of alligator populations throughout the Southeast,combined with human population growth and encroachmenton wetland habitats, has increased the likelihood of gator-humaninteractions. Even so, the fact remains that the probability of analligator attacking aperson is extremelylow. The number ofalligators throughoutthe range at any givenpoint in time isprobably more thanthree million animals,yet on the average thereare fewer than 10attacks per year. Themajority of attacks haveoccurred in Florida,where there have been11 fatalities during a50-year period. Mostattacks occur either because alligators have lost their naturalfear of humans (due to being illegally fed by people and learningto associate humans with food) or because they are defendinga territory. Humans can do several things to minimize the riskof attack:� Do not feed alligators, thereby causing them to become

accustomed to humans.� Do not swim in areas (especially near heavily vegetated

shorelines) where large (>6 feet) alligators are present,particularly at night/dusk when they are feeding.

� Do not attempt to capture alligators—it is dangerous andagainst the law.

� Do not approach an alligator nest or hatchlings.

������������������

Federal status“Threatened due to similarity ofappearance” to other crocodilian

speciesSize/age at maturity

6 ft./dependent on growth ratesTypical maximum size

males–13 to 14 feet,females–9 to 10 feet

Largest SRS alligator12’10” male that died in 1996

Weightvaries; adult males can be

500+ poundsLongevity

40 or more years in the wild,record 66 years in captivity

Home range sizeup to 2,000 acres for

adult malesHatchling size8 to 10 inchesClutch size20–60 eggs

Incubation periodapproximately 65 days

Teeth74 to 80

Name originAlligator is derived from the

Spanish el lagarto which means“the lizard”; mississippiensismeans “of or belonging to the

Mississippi”Ancestry

fossil records of crocodilianancestors, archosaurs, are

known from 225 million yearsago; archosaurs are thought to

have given rise to dinosaursand birds

This brochure was produced by the Savannah River EcologyLaboratory Environmental Outreach Program, in support ofPartners in Amphibian and Reptile Conservation (PARC;www.parcplace.org). Printing was sponsored by SREL(www.uga.edu/srel/), with additional program support from TheChristensen Fund and the Department of Energy. Text by DavidE. Scott, I. Lehr Brisbin, Jr., Travis C. Glenn, and William A.Hopkins. Photographs by David E. Scott(except as noted). Layout and design byLaura L. Janecek.

temperatures rose to such extremes? Byusing the combination of external andinternal temperature-sensitive transmitters,researchers learned that alligatorsresponded to thermal cues very rapidly,seeking cooler waters in coves, streamedges, or on stream bottomsonce their body temper-ature reached about91°F (33°C).

Like many wildlifespecies, alligatorsare vulnerable toenvironmental con-taminants. Becausealligators are top-levelcarnivores, they can bio-accumulate contaminantsin their tissues through the preyitems they ingest. Some environmentalcontaminants can be passed from femalealligators to eggs, potentially adverselyaffecting the health of developing offspring.Scientists at SREL are studying maternaltransfer of contaminants from females totheir offspring. On the SRS, alligators nestin a swamp downstream from a coal-burning power plant. The swamp iscontaminated with a variety of potentiallytoxic trace elements including arsenic,cadmium, and selenium (Se). Of theseelements, selenium is of great concernbecause it readily bioaccumulates andcauses developmental abnormalities whentransferred from females to developingembryos. Monitoring efforts in thecontaminated system revealed that adultfemale alligators accumulate Se andtransfer significant quantities to their eggs.Concentrations of Se in eggs and hatchlingscollected from the contaminated site are3-5 times higher than levels fromuncontaminated samples. Fortunately, theconcentrations of Se do not appear highenough to adversely affect developingoffspring; embryonic development, hatch-ing success, and hatchling size all appearnormal in clutches produced by femalealligators nesting in the contaminated area.

Alligators from the Par Pond population havealso been the subjects of contaminantstudies. Elevated levels of the radioactiveelement radiocesium (137Cs) occur in someportions of Par Pond as a result of reactoroperations. Cesium-137 mimics elemental

potassium when incorporatedinto plant and animal tissues;

in animals it tends toconcentrate in muscle

tissue. SREL studiesconcluded that al-though some indiv-iduals had elevatedlevels of 137Cs in their

bodies, there were nodetectable effects on

individual or populationhealth.

There is, however, reason for concern abouthuman consumption of alligators due to amuch more widely distributed environ-mental contaminant, mercury (Hg). Point-source pollution and atmospheric transportof this metal have resulted in many wildlifespecies having elevated Hg levels, even in“pristine” habitats. High Hg levels arecommon in wetland habitats and in top-levelpredators. Alligators are therefore primecandidates for exhibiting high Hgconcentrations. Mercury levels in the tissuesof SRS alligators, as well as those from othersoutheastern wetlands, have been analyzed.Although there are no national standards forHg concentrations in reptile meat, if thesame standards that are used for fish wereapplied to alligators (1 mg Hg/kg wet weightof tissue), then a high proportion ofalligators from the Everglades, other areasof Florida, and the SRS would be consideredunsafe for human consumption.

SREL scientists are also developing and usingmodern analytical and DNA techniques tolearn about alligators and solve environ-mental problems. For example, researchershave developed microsatellite DNA loci foralligators, which are the same type of geneticmarkers used for paternity analyses or

The American alligator, Alligator mississippiensis,occurs throughout most of the southeastern United States. Alligators

were once hunted primarily to produce leather products, which becamefashionable in the late 1800s. Untold numbers of animals were killed during

decades of unregulated hunting. Even after limited protection was put into effect insome areas in the mid-1900s, animals continued to be poached. As a result, alligator numbers

were dramatically reduced and in some regions it was feared that local populations would goextinct. Federal legislation in the 1970s and 1980s, including the Endangered Species Act of

1973 and amendments to the Lacey Act in 1981, ensured the alligator’s protection, and eventually its comeback. Todayalligator numbers are estimated in the millions and they are common throughout most of their historic range.

The story of the American alligator, both tragedy and success, is similarto that of many of its close kin, the crocodiles. Worldwide there are 23species of crocodilians; most were also hunted for food and skins,and by 1971 all crocodilians were endangered, threatened, or decliningin numbers. Habitat destruction in many countries exacerbated thedeclines. But a combination of legislation, effective law enforcement,dedicated conservationists, and innovative sustainable yield harvestingprograms reversed the decline for many species, despite continuinghabitat loss. Since the 1970s 16 of the 23 crocodilian species haveincreased in population size. However, some species, such as theChinese alligator, remain highly endangered in the wild.

The current federal protection status of the alligator remains as “threatened due to similarity of appearance” to endangeredcrocodiles (and products made from their skin). In some states alligators may be harvested using controlled hunts. Alligators arealso bred and raised in captivity for the production of meat and skins, but most of the half million farmed alligators are hatchedfrom eggs collected from the wild. The products from these tightly regulated wild harvests and alligator farms are now sold legally,providing important funds for the conservation of this species and its habitat.

HabitatAlligators live in fresh and brackish water habitats but will venture into saltwater. Alligators inhabit swamps, tidal marshes, creeks and rivers, canals, ponds,lakes, and reservoirs. In some areas alligators do something that only a fewspecies, such as humans and beavers, do—create wetland habitat. In marsh,sawgrass, and floodplain habitats gators sometimes create “gator holes,” whichprovide a refuge for many other animals during dry periods. Alligators createthe holes, which can be the size of a small backyard pool, using their snout,forefeet, and tail. Alligators are called a “keystone species” due to the stronginfluence they have on other species.

���������������

Alligator in a gator hole (photo by T.C. Glenn, SREL).

The American alligator and some crocodilespecies are prime examples of the concept of“sustainable use.” Sustainable use simply meansthat an organism is harvested at levels that canbe continued indefinitely. The specifics ofsustainable use programs vary among croco-dilian species, and among populations within aspecies in different parts of its geographic range.For example, the harvesting program foralligators in Florida differs from programs inLouisiana and other southeastern states; evenpopulations in different lakes within Florida aremanaged differently. The numbers of adultanimals that can be killed, as well as theproportions of eggs and hatchlings that can beremoved from the wild, are based on annualpopulation trends. The end result is that the legal,regulated harvest of various life stages does notharm the population, and gator and crocpopulations can thrive even as humans use themcommercially. In fact, many scientists believe thatsome crocodile species would be in far worseshape, and perhaps would have become extinct,if there were not a sustainable use managementprogram for those species. Carefully managedsustained-yield harvest programs provide directeconomic benefits to local people andcommunities, giving everyone an incentive toprotect both the species and its habitat.

human identification at crime scenes. Using these markers todetermine paternity in alligators led to the discovery that aboutone-third of all gator nests contain offspring from multiplefathers. In addition, although there are many 8-10 ft (2.4-3 m)male alligators in the gator population on the SRS, only the fewvery large males (11+ ft; 3.4+ m) sire offspring. Finally,microsatellites have been used in investigations of the effects ofcontaminants, leading to the discovery that the Hg and low-levels of radioactive contamination in some alligators on theSRS are not resulting in increased mutation rates relative togators from other populations. Continuing research will usethese genetic markers to make more discoveries about thebiology of alligators, solve other environmental problems, andeven produce a map of the alligator genome.

The recovery of alligator populations throughout the Southeast,combined with human population growth and encroachmenton wetland habitats, has increased the likelihood of gator-humaninteractions. Even so, the fact remains that the probability of analligator attacking aperson is extremelylow. The number ofalligators throughoutthe range at any givenpoint in time isprobably more thanthree million animals,yet on the average thereare fewer than 10attacks per year. Themajority of attacks haveoccurred in Florida,where there have been11 fatalities during a50-year period. Mostattacks occur either because alligators have lost their naturalfear of humans (due to being illegally fed by people and learningto associate humans with food) or because they are defendinga territory. Humans can do several things to minimize the riskof attack:� Do not feed alligators, thereby causing them to become

accustomed to humans.� Do not swim in areas (especially near heavily vegetated

shorelines) where large (>6 feet) alligators are present,particularly at night/dusk when they are feeding.

� Do not attempt to capture alligators—it is dangerous andagainst the law.

� Do not approach an alligator nest or hatchlings.

������������������