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Crocodilians
There are 24 species of crocodilians in the world, and 10 of those species are listed as either vulnerable, endangered, or critically endangered according to the International Union for Conservation of Nature (IUCN). One of the major causes for decline in these species is human activities such as overexploitation and habitat loss from increasing development. In addition, crocodilians face persecution since they are large predators that are viewed as threats to people and their livelihoods. It is critical to understand how these reptiles are adapting to live in human-dominated landscapes.
American Alligator (Alligator mississippiensis)
American alligators (Alligator mississippiensis) are unique among crocodilians because, unlike most crocodilians, alligators’ natural range includes areas outside of tropical regions, ranging across much of the southeastern United States. Alligators can be found from North Carolina to Florida and as far west as Texas. Male alligators can grow to be 4.6 meters (~15 feet) long, while females usually do not exceed 3.8 meters (~9 feet). Due to demand for their meat and hides, alligators historically suffered severe consequences from overharvesting. As a result of this decline, alligators were placed on the Endangered Species List. With this protection from human threats, alligator populations flourished and their increasing numbers led to their removal from the Endangered Species List in 1987. At the same time, human populations were also expanding, often encroaching into alligators’ natural habitats. This significant habitat overlap has led to a large number of conflicts between the two species. While alligator attacks on humans are exceedingly rare, they are often sensationalized in the media. Usually when humans and alligators have negative interactions, alligators are on the losing side. Alligators are hit while crossing roads, struck by boats, and ingest plastic and other trash. Additionally, large alligators get reported as “nuisance” animals and are either relocated or destroyed. Understanding how alligators use space in developed landscapes and how human activity is affecting these animals is important in effectively managing alligator populations in a modern world.
American Crocodile (Crocodylus acutus)
American crocodiles (Crocodylus acutus) are the only other crocodilian native to the United States and only persist in the southernmost portion of Florida. The extent of its range lies within much of Central America and northern South America. Although they inhabit freshwater ecosystems, crocodiles seem to prefer higher salinity waters and are often associated with coastal habitats. American crocodiles grow to be much larger than alligators; males can reach lengths of 6 meters (~20 feet) and females can be as large as 3.8 meters (~12 feet). Like the alligator, American crocodiles were hunted unsustainably for their hides in the beginning of the 20th century. This led to a severe decline in populations across their range. Furthermore, this species nests along shorelines and uses coastal regions as critical habitat. With an ever increasing demand for development along coastlines, American crocodile habitats are being degraded and destroyed. This development, along with illegal hunting, have limited the species' ability to recover effectively. American crocodiles are still protected both nationally and internationally. The IUCN identifies population monitoring and analyzing habitat requirements as research that is needed to ensure this species continues to recover across its range.
Spectacled Caiman (Caiman crocodilus)
Spectacled caimans (Caiman crocodilus) are much smaller than both alligators and crocodiles. Males rarely exceed 2.5 meters (~8 feet) while females are usually 1.4 meters long (~4 feet). Despite their size, they are much more widespread than alligators and American crocodiles. Their native range is Central America through much of South America. Spectacled caimans have opportunistically thrived in areas where other crocodilian populations have been depleted, and they have been introduced as an exotic species in southern Florida. Unlike alligators and American crocodiles, spectacled caimans have escaped much of the pressures of overharvesting by humans. However, some populations remain locally threatened and taxonomic work has continued to lead to discoveries of new subspecies. Many countries implement conservation programs independently of the IUCN as spectacled caimans are labeled as a species of least concern on this list. However, further information is needed to understand how this species uses habitat and acts in the presence of larger crocodilian species such as the American crocodile.
Research Methods
One of the first steps in studying crocodilians is to quantify the size and structure of the populations. Census surveys can be used to estimate the number of individuals in a population and their size distribution (e.g., how many are in each age class [adults, juveniles]). Crocodilians are highly cryptic animals, but we can count crocodilians by the eye-shine reflected by spotlights used in night surveys. However, it is difficult to estimate the sizes of individuals at night, so we couple these spotlight surveys - which are more effective at counting the numbers of animals - with morning surveys where we can estimate more accurately how many individuals are in different size classes using binoculars. Additionally, capture-mark-recapture studies are used to apply unique marks to animals that allow us to distinguish the individuals, thereby generating more reliable population estimates. These studies can also be used to learn about the growth rates of individuals and sex ratio of the populations.
After determining the basic population size and structure, the next step in studying crocodilians is to learn how they are using their habitat by researching their spatial ecology. While capture-mark-recapture studies can offer indications of preferences by gathering coarse movement data, modern technology has made studying spatial relationships more achievable. By using a combination of VHF radio telemetry and GPS or satellite data recording, large datasets of crocodilian habitat use and movement information can be obtained.
Crocodilians are apex predators that have long lifespans, often exceeding 60 years old in the wild. As a result, they have a tendency to bioaccumulate ecological contaminants, such as heavy metals and persistent organic pollutants. During our mark-recapture efforts, we are collecting tissue and blood samples to be analyzed for contaminants like lead, mercury, and polychlorinated biphenyls. Analyzing these contaminant loads is critical to understanding how ecological toxins are moving through the food chain and affecting top predators that serve as important regulators of prey species. Tissue and blood are additionally stored to be used in genetic studies.
Teaming Up on Tracking Alligators
We are actively seeking sponsorship for satellite tags to track American alligators in the Okefenokee Swamp! If you are interested in sponsoring a satellite tag for this exciting project, please contact Kristen Zemaitis at kzemaitis@uga.edu!
Additionally, the Okefenokee Swamp Alligator Project has its own Amazon Wish List for all the equipment needed to study alligators in the Okefenokee Swamp. You can also make a donation to the project through the University of Georgia's crowdfunding website.