Wild Alligators Research Articles

Conquering the crush: A novel tool for holding crocodilian jaws open

AbstractCrocodilians have diverse snout shapes ranging from the long, narrow snouts of the Indian gharial (Gavialis gangeticus) to the broad snout of the American alligator (Alligator mississippiensis). In addition, crocodilians possess the strongest bite force of all extant animals, with recorded values for adult alligators exceeding 9 kilonewtons (kN). Jaw‐closing pressure poses a challenge and safety risk for people working with crocodilians, such as veterinarians, wildlife managers, and researchers who must safely access the oral cavity to perform veterinary procedures, health assessments, hook removals, or sample collection. Conventionally, polyvinyl chloride (PVC) or metal tubes (pipes) placed longitudinally into the mouth have been used to hold crocodilian jaws open for such operations. The short sections of opaque pipe can cause oral irritation, obscure the palate and tongue, and restrict access to the oral cavity and palatal valve. In conjunction with a project investigating the diet of alligators in the southeastern United States, we identified a need to create an efficient tool to allow safe and direct access to the alligator oral cavity. We built 2 versions of a device for holding alligator jaws open that are adjustable to accommodate different gape sizes. The device allows for safe positioning within the mouth, includes safety considerations for device failure, and is adaptable to both widen and collapse the gape of the mouth. We successfully deployed and recovered the device on 76 wild alligators ranging in total length from 120 to 329 cm. We also performed mechanical tests in the laboratory to assess the maximum force the devices and associated materials can safely withstand, as well as the conditions under which the devices fail. Our medium‐duty and heavy‐duty device designs withstood forces up to 6 kN and 18 kN, respectively. We observed no material fracture in the devices but did observe deformations of materials used during laboratory testing. The device is an inexpensive and effective tool for veterinarians, wildlife researchers, and managers who need to hold open the jaws of crocodilians safely.

American alligator (Alligator mississippiensis) weight gain in captivity and implications for captive reptile body condition.

The body condition of an animal is an indicator of health status and is dependent upon many factors, some of which can vary between wild and captive settings. Despite this, there have not been many studies on how captivity affects body condition relative to wild animal populations. This study explores the body condition of captive and wild American alligators (Alligator mississippiensis) because reptiles are frequently overlooked in studies of captive animal health and because alligators are well-represented in captivity. We collected body condition data from 209 captive alligators and 935 wild alligators throughout Florida and southeastern Georgia and compared the relationships between body condition and body length for each group. We found that captive alligators exhibited significantly higher body condition values as they aged, and that this result was driven by the difference between captive and wild males. Body condition values for captive juveniles did not differ from wild juveniles, but they differed when comparing adults. Our results suggest that factors such as diet and movement rates play major roles in determining alligator body condition and that body condition may be an important metric for monitoring captive alligator health, especially for older adult males.

Tissue Distribution of Mercury in the Bodies of Wild American Alligators (Alligator mississippiensis) from a Coastal Marsh in Louisiana (USA).

Total mercury (THg) concentrations were measured in wild alligators inhabiting a coastal marsh in southern Louisiana, to determine the tissue distribution of THg among various body organs and tissue compartments. Concentrations of THg in claws and dermal tail scutes were compared to those in blood, brain, gonad, heart, kidney, liver, and skeletal muscle to determine if the former tissues, commonly available by non-lethal sampling, could be used as measures of body burdens in various internal organs. Mercury was found in all body organs and tissue compartments. However, overall, THg concentrations measured in alligators were below the FDA action level for fish consumption and were comparable to previous data reported from southwestern Louisiana. Our results suggest consumption of meat from alligators found in this region may be of little public health concern. However, the extended period of time between sampling (in this study) and the present-day highlight the need for continuous, additional, and more recent sampling to ensure consumer safety. Total mercury concentrations were highest in the kidney (3.18 ± 0.69mg/kg dw) and liver (3.12 ± 0.76mg/kg dw). THg levels in non-lethal samples (blood, claws, and dermal tail scutes) were positively correlated with all tissue THg concentrations (blood: R2 = 0.513-0.988; claw: R2 = 0.347-0.637, scutes: R2 = 0.333-0.649). Because THg concentrations from blood, claws, and scutes were correlated with those of the internal organs, non-lethal sampling methods may be a viable method of estimating levels of THg in other body tissues.

Quantifying Circulating IgY Antibody Responses against Select Opportunistic Bacterial Pathogens and Correlations with Body Condition Factors in Wild American Alligators, Alligator mississippiensis.

Simple SummaryImmunoglobulin Y (IgY) was purified from American alligator, Alligator mississippiensis, serum and used to develop a monoclonal antibody (mAb AMY-9) specific for the heavy chains of IgY. This antibody tool was then used to develop an ELISA for quantifying serum antibody responses against whole bacterial pathogens in alligators sampled in Florida, USA and South Carolina, USA. Antibody responses against some of the bacteria were very robust and varied by location and year, and in general these antibody responses correlated well with body condition factors, such as body-mass-indices (BMI). A novel mAb is now available to the scientific community interested in disease ecology of alligators.Little is known about the disease ecology of American alligators (Alligator mississippiensis), and especially how they respond immunologically to emerging infectious diseases and zoonotic pathogens. In this study, we examined serum samples collected from wild alligators in Florida (2010–2011) and South Carolina (2011–2012, 2014–2017) for antibody responses to multiple bacteria. Immunoglobulin Y (IgY) was purified from serum to generate a mouse monoclonal antibody (mAb AMY-9) specific to the IgY heavy chain. An indirect ELISA was then developed for quantifying antibody responses against whole cell Escherichia coli, Vibrio parahaemolyticus, Vibrio vulnificus, Mycobacterium fortuitum, Erysipelothrix rhusiopthiae, and Streptococcus agalactiae. In Florida samples the primary differences in antibody levels were between January–March and late spring through summer and early fall (May-October), most likely reflecting seasonal influences in immune responses. Of note, differences over the months in antibody responses were confined to M. fortuitum, E. rhusiopthiae, V. vulnificus, and E. coli. Robust antibody responses in SC samples were observed in 2011, 2014, and 2015 against each bacterium except E. coli. All antibody responses were low in 2016 and 2017. Some of the highest antibody responses were against V. parahaemolyticus, M. fortuitum, and E. rhusiopthiae. One SC alligator estimated to be 70+ years old exhibited the highest measured antibody response against V. parahaemolyticus and M. fortuitum. By combining data from both sites, we show a clear correlation between body-mass-indices (BMI) and antibody titers in all six of the bacteria examined. Our study provides a critical antibody reagent and a proof-of-concept approach for studying the disease ecology of alligators in both the wild and in captivity.

A comparison of stress levels in farmed and wild American alligators: an indicator of animal health and best farming practices

ABSTRACT Blood was collected from alligators at a large alligator farm in Louisiana to compare stress levels to those in wild alligators. The measurement of corticosterone (CORT) levels and heterophil/lymphocyte ratios were used to assess stress levels because both parameters become elevated during periods of physiological stress. We compared CORT concentrations and H/L ratios in wild animals that were either the same size or the same age class as farmed alligators. Plasma CORT levels and H/L ratios were no higher than those in wild alligators. To ensure consistent results across the farm, we compared plasma hormone concentrations in animals of the same size classes maintained in different enclosures and also in different buildings and found no differences. We believe that results such as these obtained from independent laboratories can be used as evidence for regulatory agencies that crocodylian farms raise their animals in low stress environments under Best Management Practices guidelines.

Correlations between environmental salinity levels, blood biochemistry parameters, and steroid hormones in wild juvenile American alligators (Alligator mississippiensis)

American alligators (Alligator mississippiensis) inhabit freshwater wetlands that are vulnerable to salinization caused by anthropogenic alterations to freshwater flow, in addition to storm surges, sea level rise, and droughts. Salinization of coastal freshwater habitats is a growing concern in a changing climate due to increased frequency and intensity of storm surges and drought conditions. This study opportunistically sampled juvenile male and female wild alligators in various salinities each month excluding November, December, and January for one year at Rockefeller Wildlife Refuge in coastal Louisiana. Blood plasma biochemistry parameters including electrolyte levels were subsequently measured. In addition, levels of various renin–angiotensin–aldosterone system hormones, glucocorticoids, androgens, estrogens, and progestogens were analyzed using liquid chromatography and tandem mass spectrometry. Only males were sampled in hyperosmotic environments (> 10‰) during dry conditions in late summer 2018. In juvenile males, plasma Na+, Cl−, and the progestogen 17α,20β-dihydroxypregnenone were significantly and positively correlated with environmental salinity. However, variation in glucocorticoids, androgens, and estrogens were not associated with hypersaline water while sex steroids showed significant seasonal variation. This study demonstrated significant correlation of environmental salinity with electrolyte levels and a sex steroid in wild juvenile alligators, and to our knowledge represents the first measurement of 17α,20β-dihydroxypregnenone in alligators.

Marshmallows for Alligators: Defining Ecotourism in Southwest Florida

AbstractShould an ecotour operator feed marshmallows to wild alligators in the Florida Everglades? Observing the operator encourage alligators to approach an airboat so that the tourists onboard could see them provoked questions about what ecotourism is and what value it has for both the tourist industry and resource preservation. Is ecotourism merely a new label for an old product or is it a real effort to reengage the public in our natural and cultural heritage resources, but in an environmentally sensitive and culturally appropriate way? To answer this question, this paper considers how the ecosystem service or natural resource capital model can help reconcile what ecotourism offers to both the traveling consumer and to those tasked with measuring and protecting our natural resources.

Relationship between nest defence behaviours and reproductive benefits in Chinese alligators

The evolutionary theory in parental care predicts that parents may defend more vigorously of nests with higher survival and reproductive benefits. Based on this prediction, we proposed that the occurrence of nest defence behaviours in Chinese alligators might be connected to reproductive benefits (clutch size, fertility rate, and hatching rate). In this study, we examined the relationship between the occurrence of nest defence behaviours and (1) the variations in clutch size, fertility rate, and hatching rate of wild Chinese alligators, and (2) the variations in clutch size and fertility rate of captive Chinese alligators in a semi-natural facility. Results showed that for the wild Chinese alligators, the fertility and hatching rates with nest defence behaviours were higher than those without nest defence behaviours. The results also showed that for the captive Chinese alligators, the fertility rates with nest defence behaviours were higher than those without nest defence behaviours. These results suggested that nest defence behaviours in Chinese alligators might be relative to reproductive benefits, thus likely to further improve the probability of the species’ reproductive success.

Mercury contamination in alligators (Melanosuchus niger) from Mamirauá Reservoir (Brazilian Amazon) and human health risk assessment.

Mercury (Hg) concentrations in muscles of wild alligators (Melanosuchus niger) from the Mamirauá Reservoir (a reference area in the Brazilian Amazon) and the human health risks associated with its consumption were assessed. The mean Hg concentration in alligator muscles was 0.407 ± 0.114 μg/g (N = 61). Close to 5 % of the muscle samples showed Hg levels above the World Health Organization guideline for fish consumption (0.5 μg/g). A positive and significant relationship was observed between Hg concentrations in muscle and the age of the specimens. The dose-response approach suggests that close to 27.4 years is required for half of the exposed specimens to attain 0.5 μg/g. The hazard quotient (HQ) is a risk indicator which defines the ratio of exposure level and a toxicological reference dose. HQ resulted above the unity for all the specimens when the ingestion rate for riverine communities (200 g of muscle per day) is considered, indicating the existence of hazard. When the ingestion rate for market consumers (28.57 g/day) is considered, the risks are much lower (mean HQ = 0.55), suggesting that such group is not at risk. The establishment of local and regional ingestion rates for riverine populations and market consumers is extremely recommended.

The sex ratio of wild Chinese alligators Alligator sinensis

Abstract The Chinese alligator Alligator sinensis is one of the most endangered crocodilian species, and typically exhibits temperature-dependent sex determination. It is extremely important to clarify the sex structure of Chinese alligators to implement recovery projects successfully. However, the sex ratio of wild Chinese alligators remains unknown. In this study, we collected 28 years of sex ratio data from Chinese alligators residing in the natural and artificial habitats of Changxing Nature Reserve, China, and examined the differences in the sex ratio dynamics between these two populations. We observed that the sex ratio of wild Chinese alligators is 1 male to 4.507 females, which was significantly lower compared to that of the captive population (1 to 2.040; P < 0.001), and is significantly different to previously documented sex ratios for this species (all P < 0.01). Furthermore, we documented an annually stable (P = 1.000) female-biased sex ratio for wild alligators at hatching [1 male to 4.747 females; 0.174 (0.167–0.182)], in contrast to a dramatically fluctuating sex ratio (P < 0.001) in captivity [1 male to 1.674 females; 0.374 (0.246–0.593)], showing a potential mechanism for adjusting the sex structure. Finally, we found that the hatchling sex ratios were similar to that of the population sex ratio (P = 0.748), with little correlation to air temperature values in the 60–70 day incubation period during the breeding season (July and August; both P > 0.05). Overall, this study indicates that the stabilized female-biased sex ratio of Changxing Chinese alligators might result from selection pressure caused by local mate competition and major inbreeding.

American Alligator Digestion Rate of Blue Crabs and Its Implications for Stomach Contents Analysis

Stomach contents analysis (SCA) provides a snap-shot observation of a consumer's diet. Interpretation of SCA data can be complicated by many factors, including variation in gastric residence times and digestion rates among prey taxa. Although some SCA methods are reported to efficiently remove all stomach contents, the effectiveness of these techniques has rarely been tested for large irregular shaped prey with hard exoskeletons. We used a controlled feeding trial to estimate gastric residency time and decomposition rate of a large crustacean prey item, the Blue Crab (Callinectes sapidus), which is consumed by American Alligators (Alligator mississippiensis), an abundant apex predator in coastal habitats of the southeastern United States. The decomposition rate of C. sapidus in the stomachs of A. mississippiensis followed a predictable pattern, and some crab pieces remained in stomachs for at least 14 days. We also found that certain portions of C. sapidus were prone to becoming caught within the stomach or esophagus, meaning not all crab parts are consistently recovered using gastric lavage techniques. However, because the state of decomposition of crabs was predictable, it is possible to estimate time since consumption for crabs recovered from wild alligators. This information, coupled with a detailed understanding of crab distributions and alligator movement tactics could help elucidate patterns of cross-ecosystem foraging by the American Alligator in coastal habitats.

Extremely high major histocompatibility complex class IIb gene intron 2 variation and population structure in Chinese alligator

Identifying the processes that maintain genetic diversity within and among populations is a central goal of modern evolutionary genetics. So far, the studies on genetic diversity have mainly focussed on neutral DNA markers, such as mtDNA and microsatellites (Xu et al. 2010). While these markers are very informative in molecular clocks, to examine dispersal patterns of individuals (gene flow) and to classify them by relatedness and paternity analyses. The variation at neutral loci cannot provide direct information on selective processes involving the interaction of individuals with their environment or on the capacity for future adaptive changes (Sommer 2005). With the developments in molecular biology, researchers can directly examine selection at genes that underlie functional traits. Therefore, adaptive nonneutral markers have become especially valuable (Koskinen et al. 2002). One important example comes from the genes of the major histocompatibility complex (MHC). These genes are found in all jawed vertebrates and play a critical role in an organism’s immune response (Karaiskou et al. 2010). High levels of variation in MHC alleles are believed to confer the ability to recognize a wide range of antigens and thus increase resistance to a greater number of environmental pathogens. Chinese alligator (Alligator sinensis) is one of the 23 critically endangered crocodile species in the world. The wild population has been close to extinct during the past decades due to habitat loss and illegal hunting. The investigation indicated that the number of wild Chinese alligators has decreased from 500 individuals in the 1980s to currently less than 120 or 150 individuals (Thorbjarnarson et al. 2002).

Studies of Metals in Crocodilians by Spectrochemical Methods

: This review covers the results of metal determinations using various spectrochemical analytical techniques in crocodilians from various geographical regions. The most widely determined metal is mercury, both inorganic and organic. However, many other metals, including the known toxic metals of lead and cadmium, have been determined. In general, more elevated levels of metals have been determined in crocodilians from potentially contaminated as opposed to more pristine areas. Significant differences in concentrations for many metals have been demonstrated in captive versus wild alligators. The part of crocodilians most widely utilized for food, tail or tail meat, has attracted the most interest, but studies on kidney and liver as well as blood have been reported. Eggs and hatchings have also been examined for several metal concentrations.

Testing reintroduction as a conservation strategy for the critically endangered Chinese alligator: Movements and home range of released captive individuals

The Chinese alligator (Alligator sinensis) is considered the most critically endangered crocodilian as a result of the near total loss of its habitat and its extremely small and fragmented wild populations. Plans for population recovery lie mostly with wetland restoration and the reintroduction of captive-reared animals. We carried out a first-trial release of 3 adult Chinese alligators (1♂, 2♀) into a pond at the Hongxing conservation site, Xuancheng, southern Anhui Province; the animals were radio-tracked from May to October in 2003. We hypothesized that after a period of adaptation, the alligators would establish definable home ranges. Two (1♂, 1♀) of the 3 alligators were monitored for the whole of the tracking period. The male had an annual home-range size of 7.61 hm2, and the female 4.00 hm2. Water temperature and pond water level were two important factors influencing the alligators’ distributions, and daily movements. The radio-tracked alligators had overlapping home ranges, which notably included the one substantial island in the pond; that island is the only known nesting site of the local native wild alligators. Aggressive interactions between the released alligators and native wild alligators were observed during the breeding season around this island. All the three reintroduced alligators survived the winter of 2003 and were alive in the same pond in 2008. We concluded that the Hongxing conservation site provided a suitable habitat for the reintroduced alligators. However, the low water level in the pond resulting from farmland irrigation in August and September can be a substantial threat to the alligators’ survival. Therefore, regulations on irrigation in summer and autumn are needed to balance the water needs of the alligators and agriculture.

Report of case: leptospirosis after exposure to alligator carcass

In the past decade, leptospirosis has emerged as a globally important infectious disease. Mortality remains significant; this may be related to delays in diagnosis because of lack of infrastructure and adequate clinical suspicion, and to other poorly understood reasons that may include inherent pathogenicity of some leptospiral strains or genetically determined host immunopathological responses. Leptospirosis is a spirochete parasitic bacterium most commonly reported from rodents and contracted through contact with rodent urine, but also reported from cows and other domestic animals and contracted through contact with contaminated water. Humans are infected by direct contact with animals or through exposure to fresh water or soil contaminated by infected animal urine. Leptospires enter the body through cuts and abrasions, mucous membranes or conjunctivae, or aerosol inhalation of microscopic droplets. From 1995-1998, approximately nine people working with alligators in south Florida have apparently contracted leptospirosis. All of the victims were working with wild alligators; most had contact with alligator nests and nearly half required hospitalization. Although it has been postulated that leptospires may be transmitted directly from infected, large reptiles to the hands of handlers, it has been felt that it was probably more likely that handlers were indirectly exposed by water contaminated with the urine of leptospiruric reptiles or that the swamps and waterways from which eggs are harvested are contaminated by the infected urine of rodents or other animals. This report describes a case in which a Florida State Trooper became symptomatic after removal of an alligator carcass from a south Florida roadway.

Gizzard Shad Thiaminase Activity and Its Effect on the Thiamine Status of Captive American Alligators Alligator mississippiensis

Adult mortality and low egg hatch rate were observed among American alligators Alligator mississippiensis in Lake Griffin, Florida, between 1998 and 2003. Previous studies show that the alligator mortality is due to neurological impairment associated with thiamine (vitamin Bt) deficiency. This study determined the rate of thiaminase activity in gizzard shad Dorosoma cepedianum, a fish often eaten by alligators, and examined the thiamine status of captive adult alligators fed only gizzard shad. We found that the thiaminase activity of gizzard shad in Lake Griffin is 16,409 +/- 2,121 pmol/g/min (mean +/- 2SEs). This high rate of thiaminase activity was present in most months and across a wide range of shad sizes. Seven alligators were captured in the wild from Lake Griffin and Lake Woodruff, held in captivity, and fed gizzard shad. We monitored blood and muscle thiamine levels throughout the experiment and liver thiamine at the end. Over a period of 6-12 months, all of the alligators maintained weight but blood and muscle thiamine levels decreased to 25-50% of the original (healthy) values. Three animals with the greatest reduction in thiamine died, demonstrating mobility impairment and neural histopathology similar to those seen in wild alligators in Lake Griffin. Two alligators were fed shad for 10 months but then treated with thiamine. These animals showed a reduction in thiamine while eating shad, but treatment restored their thiamine levels to the initial values, which were comparable to those of normal wild Lake Griffin alligators. We demonstrated that thiamine deficiency can be induced by a diet of gizzard shad and cause neurological signs and death in alligators in captivity. We conclude that the thiaminase activity in gizzard shad is high enough to cause thiamine deficiency in wild alligators when shad are a major part of their diet.

Parental Exposure to Pesticides and Poor Clutch Viability in American Alligators

In central Florida, alligators (Alligator mississippiensis) inhabiting lakes contaminated with organochlorine pesticides (OCPs) produce eggs that have high OCP concentrations and low clutch viability (proportion of eggs in a clutch that yield a live hatchling) compared to those from less contaminated lakes (reference lakes). However, a clear dose-response relationship has not been established between OCPs and poor clutch viability. In order to better elucidate a cause and effect relationship between OCP exposure and clutch viability, we conducted concurrent field and laboratory studies. Our field study reaffirmed that eggs of wild alligators from OCP-contaminated lakes and wetlands continue to have lower clutch viability and higher OCP burdens than eggs from reference lakes. Our field study also demonstrated that OCP egg burdens were strongly correlated with clutch viability for some of the OCP-contaminated sites, but not all. To better test causal relationships, a parental exposure study was conducted using captive adult alligators. Our laboratory study demonstrated that dietary exposure of captive alligators to an ecologically relevant OCP mixture caused alligators to produce eggs with higher OCP burdens and reduced clutch viability, as compared to the captive-control population. The experimentally induced egg burdens and clutch viability reductions were similar to those of wild alligators from OCP-contaminated sites. Our field and laboratory results suggest parental OCP exposure may be contributing to low clutch viability in wild alligators inhabiting OCP-contaminated habitats, raising some concern for endangered crocodilians living in OCP-contaminated habitats.

Broad spectrum antimicrobial activity of leukocyte extracts from the American alligator ( Alligator mississippiensis)

Leukocytes were isolated from whole blood of wild alligators by differential sedimentation. The leukocytes were disrupted in 5% AcOH and the crude extracts processed by ultrafiltration. The extracts were subjected to solvent exchange (0.1% AcOH) and the fraction that contained macromolecules between 1 and 10 kDa were subjected to further analyses. The acid extracts of the alligator leukocytes exhibited substantial antimycotic activities against six of eight species of Candida yeast tested. In addition, the alligator leukocyte extracts were effective as antimicrobial agents against 10 of 12 bacterial species, and displayed moderate activity against two enveloped viruses (human immunodeficiency virus-1 and herpes simplex virus-1 HF). Kinetic analyses revealed that the antimycotic effects of the leukocyte extract occurred rapidly, with 64% fungal growth inhibition within 3 min of exposure. The molecule(s) responsible for the antimicrobial activities were sensitive to proteases, heat-stable, acid soluble, and in the 1–10 kDa range. These data suggest that alligator leukocytes express cationic peptides that are responsible for their antimicrobial properties.

Chronic incidental lead ingestion in a group of captive-reared alligators ( Alligator mississippiensis): Possible contribution to reproductive failure

An American alligator ( Alligator mississippiensis) breeding facility using male and female alligators raised from artificially incubated eggs was established in 1975. These alligators first reproduced at 6 years of age as compared to 10–12 years in wild alligators, but the eggs produced showed a lower hatching rate than those collected from the wild. By age 21 reproduction had failed almost completely. The alligators were sacrificed and tissues collected at necropsy from 44 captive and 15 wild animals and assayed for metals. Results showed that captive alligators had significantly higher tissue levels of lead than wild alligators. Cadmium did not differ between wild and captive and selenium was 50% higher in wild than captive alligator kidneys. Bone lead in captive alligators was 252,443 ± 20,462 ng/g. High yolk lead was suggested as a probable cause for early embryonic death in alligator eggs. The high tissue lead levels in captive alligators was attributed to long-term consumption of nutria ( Myocastor coypus) meat contaminated with lead shot. Liver, ovary, and testis were assayed for lipid peroxidation using the thiobarbituric acid (TBA) test. Captive alligators had 3.6 fold increased TBA-reactive materials in the liver tissue compared to wild. Lipid peroxidation was strongly suspected as having been enhanced by consumption of rancid nutria meat containing lead.

Laser ablation ICP–MS analysis of the radial distribution of lead in the femur of Alligator mississippiensis

A laser ablation ICP–MS technique has been used to examine the radial distribution of lead in transverse sections of alligator femur. Annual bone growth in the femur results in the deposition of incremental layers of calcified tissue at the periphery of existing bone. Patterns of lead concentration within these layers provide a record of time-dependent accumulation from which exposure history can potentially be deduced. Femur specimens obtained from captive-reared alligators exhibited levels of lead accumulation that were entirely consistent with previously documented clinical signs of lead intoxication. In contrast, femurs obtained from wild alligators contained only minor amounts of lead that were likely accumulated as a result of incidental exposure.