Many people who learn of my penchant for kayaking in southern swamps ask “what about alligators?” I make no effort to get nose-to-nose with alligators, but I get a thrill out of seeing them. I don’t bother them, and they don’t bother me. No alligator has ever acted aggressively toward me. If they see me coming, as I get closer they will generally submerge if they are in the water or slide into the water if they are on the bank. If I surprise one, they will thrash into the water in a noisy, splashy hurry, but though they’ve startled me, they’ve never attempted to attack or intimidate me or my boat.
The Gulf Coast in general, and Louisiana and Florida in particular, are the gator capitals of the USA. As cold-blooded reptiles they appreciate the near-tropical warmth, and the American alligator Alligator mississippiensis grows faster and larger, on average, than further north. North Carolina is the northern limit of the alligator along the Atlantic coast, though as the climate warms, they may be edging into Virginia in the Great Dismal Swamp area.
Alligators are denizens of swamps, marshes, slow-moving coastal plain streams, and lakes. As waterfront land is devoured by development, and wetlands historically altered by dredging, filling, and artificial drainage, gator habitat has dwindled. However, human modifications of the environment have not always been detrimental.
In South Carolina, prime habitat was created by wetland alteration for rice cultivation, which began in Charleston around 1680. Ditch and dike construction modified natural drainage, resulting in extensive changes in wetland plant communities. Abandoned, diked rice fields began to deteriorate after the rice industry collapsed in the early 1900s, but some of the water control structures were repaired and maintained by hunters for waterfowl hunting. According to the S.C. Division of Natural Resources these impoundments host the highest alligator population densities in the state.
Though far more active in warmer times, S.C. alligators may be active year-round. June is the peak time for nest construction and egg laying in the Carolinas. Nests are generally on higher ground (a relative term indeed in marshes and swamps) within about 5 m (16 ft) of the water. According to the SCDNR, in the ACE (Ashepoo, Combahee, and Edisto) basin between Charleston and Beaufort, SC nest material is typically big cordgrass (Spartina cynosuroides), which is generally consistent with what I have seen in the field, at least where big cordgrass is present. Nests are about 1.5-1.8 m (5 or 6 ft) across and about 0.5 m (20 in) tall.
Gator in the Waccamaw River, SC
As with humans, alligator food habits vary with age and size. Hatchlings supplement their yolk reserve with insects, crustaceans, snails, and small fish. Grownups feed on aquatic fauna and animals that venture to the water’s edge. In estuaries, they’ll often eat blue crabs, and occasionally on dead meat (carrion). At maturity, gators are apex carnivores with no natural predators (unless you count humans). They’ll eat deer, raccoons, wading birds, semi-aquatic mammals such as beaver and nutria, and occasionally snakes and turtles. The latter apparently know when a gator is not hungry enough to crunch them, as I’ve seen turtles sunning peacefully next to alligators on the same log.
Alligators do not seek to eat humans—we’re too big. Alligator attacks on humans, while rare, can occur. Gators are shy and would rather avoid human contact. But they may become aggressive if they feel threatened, if they are provoked, or if they are protecting their nests or young. Most attacks happen when humans enter alligator habitats, such as swamps, marshes, or rivers; or when alligators occupy human-created habitats such as the ever-proliferating stormwater detention and golf course ponds of the Carolinas.
In the Carolinas alligator-infested waters occasionally freeze, and temperatures near or below freezing can be fatal. However, by staying in their dens they can survive. A study in Lake Ellis Simon near Havelock, NC in the early 1980s showed another adaptive behavior when the lake froze. Gators were observed mostly submerged, but with their snouts just above the water—in one case with the tip of the snout surrounded by, and possibly locked into, the ice. North of N.C. the cold weather prevents reproduction by restricting breeding, nesting, and hatching, but there are cases of transported alligators in more northerly locations that survived for several winters (2).
By the way, the oft-told tale of alligators living in the sewers of New York city is a myth. Transported alligators have been seen and caught in the city, and small dead ones have been found in the sewers, likely former pets that outlived or outgrew their welcome. But the idea that the NYC sewers host reproducing populations of large alligators is a great story, but just that—a story (3).
My impression in North Carolina waters I have frequented since the late 1970s, is that alligators are far more frequent than in the 1980s and 1990s. Back in the day I very rarely ever saw one; now I see them frequently. Other paddlers, fishermen, scientists, etc. who frequent the swamps that I’ve talked to generally have the same impression. But data are scarce. If you search online for how many alligators are in N.C., several sources will tell you that there are about 1000, usually with no indication of where that number comes from (though in one case it is attributed to the state Department of Forestry and Natural Resources, a non-existent agency). That number is too low, I am confident, though it may have been applicable decades ago, when populations were still recovering. I’ve seen about 50 in my current home county alone (Craven County), and there bound to be at least a dozen I didn’t see for every gator that I laid eyes on. That gets us to 600 right there, not counting swamps in Craven County I haven’t visited yet, and at least 24 other N.C. counties where the animals are known to occur.
In 2012-2013 a group from N.C. State University surveyed alligators in 25 coastal counties where gators were previously known to exist. They used multiple detection methods and some sophisticated statistics to predict alligator occupancy based on habitats and environmental variables (see figure below). The distribution was similar to that found in the only previous survey 30 years early. They did note that “there is some indication the population may have increased in certain areas” (4).
In the early to mid-20th century alligator populations nationally declined precipitously due to hunting for food, leather, and sport. They received various levels of legal protection from the early 1960s and were protected under the 1973 federal Endangered Species Act. Populations increased, and the alligator was delisted (from endangered to threatened) in 1987, and populations in the Carolinas seem to have increased since then to the point that limited permit-based hunting is allowed in the Carolinas.
Though some unregulated hunting still occurs, by far the major threats to Alligator mississippiensis in the Carolinas are wetland habitat disruption and destruction, and coastal development that not only destroys and degrades habitat, but brings humans and alligators into more frequent contact—hunting and trapping of so-called “nuisance” alligators is permitted.
Alligators are ecosystem engineers as they modify habitats via nest construction and excavation of dens, holes, and tunnels that, in addition to benefitting the gators, also provides benefits for other critters. A study in Georgetown County, SC, using game cameras identified 81 different species at alligator nests from 2016-2021; a variety of birds, mammals, reptiles, amphibians, and invertebrates. They used the nests for foraging and feeding, traveling, and other purposes, including, in the words of the study, loafing (5).
Sea-level and alligators
Ongoing sea-level rise will increase the salinity in some alligator habitats. Alligators are primarily freshwater animals, but they can live in some low-salinity brackish areas and may be common in environments that are usually fresh but experience occasional low-salinity saltwater intrusion. They can tolerate saltier waters from a few hours (or maybe days), but do not live in marine or high-salinity estuarine environments. They are occasionally seen on ocean beaches, but this is rare enough that it is always a big deal. As a freshwater body or river reach gets saltier as sea-level rises, it would presumably come less suitable or unsuitable for alligators. As mobile creatures, however, they can readily migrate if suitable habitats are available. And therein lies the main issue.
As sea-level rises various swamp and marsh habitats may migrate up onto the adjacent uplands or upriver, though the extent to which this occurs depends on the slopes the landforms and ecosystems must climb. The geomorphological, hydrological, and ecological responses are more complex than a simple translation upward and inland, but there is not necessarily a net wetland habitat loss if there is room to migrate (6)
The key point is “if there is room to migrate.” If the adjacent land use is a housing development, golf course, or farm—as it often is—a transition to wetland will often not be allowed. Drainage, infilling, landscaping, vegetation management, and other tactics are often using to prevent or slow sea-level driven encroachment. If the wetland-upland boundary is a bulkhead, seawall, or other hard structure there is an unsurmountable barrier to migration. Even if increased wetness and vegetation change as sea-level rises are tolerated by the human overlords, alligators may not be.
Within a given limited area, SLR may reduce alligator habitat due to erosion and drowning. One study examined these effects for alligators and other threatened or endangered species at the Cape Romain National Wildlife Refuge, S.C. (7). The study found that while other species are at greater risk than alligators, erosion can erase habitat. Another study examined the present and future possibility for alligators to live on the North Carolina Outer Banks barrier islands. The gator’s short-term ability to tolerate saltwater enables them to get to the islands. They found the island habitat to be suboptimal, but the sites are at the extreme northern limit of the alligator’s range. Storms (tropical and extratropical cyclones or nor’easters) are a limiting factor here likely to be made more so by climate change and SLR, as well as—of course—development by humans (8).
Along most of the rivers of the Carolina coasts, the leading edge of SLR effects are in swampy bottomlands well inland of the ocean coast where the floodplains and wetlands provide a practical buffer from adjacent development. As SLR effects propagate upstream and transform habitats—my work suggests that this is occurring at a typical rate of several hundred meters per year—it will be interesting to see whether alligator populations increase (9).
Climate change and alligators
Alligators and other crocodilians are quintessential tropical and subtropical humid-region species. They simply don’t establish where it is too cold or dry. The distribution of crocodilian fossils is considered a reliable indicator of past warm and humid climates by paleontologists, based on the biogeography of modern crocodilians (10).
In general, it seems that warmer climates would allow alligators to expand their range if suitable habitats are available, and a 2013 article in Slate Magazine suggested that alligators have expanded their range into Virginia (11). If climate change allows more intense winter cold spells, however, this could limit expansion or cause increased alligator mortality. This is less intuitive than general warming allowing range expansion, but consider that the Arctic is warming faster than the rest of the planet (a phenomenon called Arctic amplification). This warming reduces temperature differences relative to northern hemisphere mid-latitudes. This in turn can cause the polar jet stream in the troposphere to become wavier and less stable. The stratospheric polar vortex, a band of cold air winds that circle the Arctic, can be weakened by a more irregular jet stream. A strong vortex keeps the coldest air locked up in the Arctic, but a weaker polar vortex is prone to instability and southward shifts. These shifts--polar outbreaks--can bring Arctic air to the midlatitudes, including the Carolinas, creating extremely cold weather, even as Earth warms overall (13).
Climate change will not turn the Carolina coastal plains into a prairie or a desert, but there is a possibility of more frequent and severe droughts. Climate models for the Carolina coastal plain under various scenarios show increasing temperatures, and various trends in precipitation—but mostly increases. However, the amount of water in soil to support plants, or running off to feed rivers and swamps is a function not only of precipitation, but also evaporation and transpiration (water used by plants). These show, in general, soil moisture storage and runoff declining, and the evaporation deficit increasing. The latter reflects the gap between potential evaporation and transpiration (essentially, the environmental “demand” for water, or how much would be evaporated and used by plants if supplies are not limited) and actual evapotranspiration. Runoff and soil moisture decreases, and evaporation deficit increases, cannot be good for gators. But whether the changes are enough to significantly influence their range and distribution is uncertain.
NOTES:
(1) Information from S.C. Department of Natural Resources, https://www.dnr.sc.gov/marine/mrri/acechar/speciesgallery/Reptiles/AmericanAlligator/index.html.
(2) Hagen, J.M., Smithson, P.C., Doerr, P.D. 1983. Behavioral response of the American alligator to freezing weather. Journal of Herpetology 17, 402-404.
(3) “The Truth About Alligators in the Sewers of New York.” Cory Kilgannon, New York Times, 26 Feb. 2020.
(4) Gardner, B., Garner, L.A., Cobb, D.T., Moorman, C.E. 2016. Factors affecting occupancy and abundance of American alligators at the northern extent of their range. Journal of Herpetology 50, 541-547. The earlier survey comes from a 1983 M.S. thesis from N.C. State University by T.G. O’Brien, later published as O’Brien, T. G., Doerr, P.D. 1986. Night count surveys for alligators in coastal counties of North Carolina. Journal of Herpetology 20, 444– 448.
(5) Rainwater, T.R., Singh, R., Tuten, C.A., et al. 2024. Fauna associated with American alligator (Alligator mississippiensis) nests in coastal South Carolina, USA. Animals 14, 620.
(6) This is something I have worked on over the years. For example: Phillips, J.D. 1989. Erosion and planform irregularity of an estuarine shoreline. Zeitschrift fur Geomorphologie Suppl. 73: 59-71; Phillips, J.D. 2011. Predicting modes of spatial change from state-and-transition models. Ecological Modelling 222: 475-484; Phillips, J.D., 2018. Coastal wetlands, sea-level, and the dimensions of geomorphic resilience. Geomorphology 305: 173-184; Phillips, J.D., 2018. Environmental gradients and complexity in coastal landscape response to sea level rise. Catena 169: 107-118; Phillips, J.D. 2023. Landscape change and climate attribution, with an example from estuarine marshes. Geomorphology 430: 108666; Phillips, J.D. 2024. Sequential changes in coastal plain rivers affected by rising sea-level. Hydrology 11, 124.
(7) Daniels, R.C., White, T.W., Chapman, K.K. 1993. Sea-level rise: Destruction of threatened and endangered species habitat in South Carolina. Environmental Management 17, 373-385. While the basic points of this article are still highly relevant—when habitats are lost to erosion, species suffer, and that is happening in S.C.—it would be interesting to revisit this as sea-level rise and its impacts have accelerated, and continue to do so, since the article was published.
(8) Parlin, A., Dinkelacker, S., McCall, A. 2015. Do habitat characteristics influence American alligator occupancy of barrier islands in North Carolina? Southeastern Naturalist 14, 33-40. The study emphasized short-term occupation and visitation by mainland alligators as opposed to establishment of semi-permanent breeding populations.
(9) Phillips, J.D. 2024. Sequential changes in coastal plain rivers affected by rising sea-level. Hydrology 11, 124.
(10) For example, see Markwick, P.J. 1998. Fossil crocodilians as indicators of late Cretaceous and Cenozoic climates: Implications for using paleontological data in reconstructing palaeoclimate. Palaeogeography, Palaeoclimatology, Palaeoecology 137, 205-271.
(11) “Alligators in your backyard.” Jackson Landers, Slate Magazine, 19 February 2013. The Virginia Department of Game and Inland Fisheries confirms sightings in the southeastern part of the state, especially in the Great Dismal Swamp area along the North Carolina border. However, the department does not consider the species native to Virginia and attributes the sightings to escaped or released captive alligators.
(12) Zhang, J., Tian, W., Chipperfield, M.P., et al. 2016. Persistent shift of the Arctic polar vortex towards the Eurasian continent in recent decades. Nature Climate Change 6, 1094-1099; Hamouda, M.E., Portal, A., Pasquero, C. 2024. Polar vortex disruptions by high latitude ocean warming. Geophysical Research Letters 51, e2023GL107567.
