Feral Hogs, Other Predators Impacting Sea Turtle Beach Nests

Extensive research on the Georgia barrier islands of the Atlantic Ocean reveals that feral swine are among the most impactful of predators on nesting sea turtle eggs.

Feral Hogs, Other Predators Impacting Sea Turtle Beach Nests

Feral hogs are linked to widespread damage of crops and landscape, and now are among the leading predators of sea turtle eggs on Georgia's coastal barrier islands. (Photo: Georgia DNR)

We’ve heard stories about feral hogs devastating a field of freshly planted pine seedlings, destroying landscaping in south Florida cities and rooting corn or other agricultural fields.

Also, of course, we’ve heard tales of hogs eating pretty much anything in their path: snakes, baby turkeys, eggs, baby deer, birds, cactus, plants and whatever they think is edible. They’re omnivores, meaning they eat plants and animals. The Texas A&M AgriLife Extension service says feral swine eat 85 to 90% vegetation and 10% animal matter, and 3 to 5% of their body weight a day depending on size and age.

Now, research along the Georgia barrier islands reveals that feral swine are among the most impactful of predators on nesting sea turtle eggs. The non-native swine, along with raccoons, lead a list of predators large and small that includes foxes, crabs and 14 species of ants. It seems everything on the 12 islands on which research was done from 2009-18 feasted on sea turtle eggs. Findings were published in the September 2020 issue of Global Ecology and Conservation.

Swine Damage

Feral swine wreak havoc throughout the country, impacting agriculture, wildlife, native species, property and more. The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (USDA-APHIS) estimates about $1.5 billion annually in damage and control costs. The agency also says hogs can threaten the health of humans, wildlife, pets and domestic animals.

While their most populous growth is in the Sunbelt states, they’re able to withstand winters and live in some harsh climates. In 2019, according to the USDA-APHIS, feral hogs were confirmed in 29 states from Hawaii to New Hampshire. This includes one county in North Dakota on the Canada border and a couple of counties in Michigan’s Upper Peninsula. They are most populous in California, Texas, Louisiana, Oklahoma, Mississippi, Alabama, Georgia, South Carolina and Florida.

Expansion is swift, as seen in Oregon’s central region. Between 2017 and 2019, feral pigs closed the gap between known populations in the north-central part of Oregon and a known population in northwest Nevada. The same happened in eastern Arizona, where pigs are moving south along the border with New Mexico.

Thanks to robust breeding cycles, succession rates and few to no predators, feral swine can quickly populate an area. Lone boars seeking new areas may find other sows, thus expanding the numbers, and the pigs generally move around seeking the best available food and water sources. 

Island Life

Coastal barrier islands are harsh, ever-changing with the wind and tides, and in undeveloped or mildly developed situations offer excellent research opportunities. Sea turtle nest monitoring has been conducted in some form on Georgia’s 14 barrier islands since 1958. The islands currently are owned or managed by the U.S. Fish & Wildlife Service, U.S. National Park Service, State of Georgia, and private or public owners.

The islands provide optimal nesting sites for sea turtles from May to October. Loggerheads are the primary species, with leatherback, green and Kemp’s Ridley sea turtles also having been documented. Predation has been known for decades, primarily from feral hogs, coyote and 9-banded armadillo. The predation research conducted by the Georgia Sea Turtle Cooperative on the island was conducted thusly:

“We analyzed loggerhead nest predation and other egg loss patterns in a long-term data set (2009 to 2018) from the Georgia coast that included 12 nesting beaches with varying nesting activity, predator richness, and human development,” they explained.

“We examined the spatial and temporal variation in egg predation, calculating mean egg loss per predation event and predation event frequency for each predator. Our objectives were to 1) determine which predators cause the greatest loss of loggerhead eggs under current management strategies; 2) evaluate whether non-native species have a higher rate of predation than native species; and 3) compare predation rates to other sources of egg loss under the current strategies for nest management in Georgia. Based on our results, we suggest management actions to enhance sea turtle nest protection and reduce egg losses from nest predation.”

Results showed predation from feral hogs, coyotes, armadillos, raccoons, red fox, gray fox, opossum, river otter, mink, birds, reptiles, crabs and 14 species of ants including fire ants. The raccoon populations on several undeveloped islands including Wassaw, Ossabaw, St. Catherine’s, Blackbeard, Little St. Simons and Cumberland, have been actively managed through trapping and hunting. Researchers said 42% of nest protection projects along the coast have used trapping and hunting to reduce feral hog populations.

“The predator removal programs for these islands have been developed with the objective to reduce the annual rate of mammalian predation to at or below 10% of nests within each recovery unit,” researchers noted.

The study said it accounted for 19,158 loggerhead nests reported from 2009 to 2018, with an average of approximately 1,916 (SE = 197.85) nests laid per year. The percentage of nests suffering egg losses (excluding research loss) ranged from 12.67% (2014) to 30.36% (2017) per year, with the number of nests suffering egg losses fluctuating with annual nest abundance; for example, 2016 had the highest number of nests laid (3,178) as well as the highest number of nests predated. Total egg loss for the study was estimated at 194,261 eggs. 

Planned Protection

Monitoring and efforts to reduce predation via hunting, trapping and protective anchored nets over nests will continue. Hogs were specifically targeted on St. Catherine’s Island in 2018 after two years of intense predation on turtle eggs. The U.S. Department of Agriculture Wildlife Services handled the culling.

Researchers said coyotes were more adept at raiding nests, “often on the first night eggs were deposited before protective nets could be installed. However, a concerted effort at trapping and removal reduced predation significantly, from 59 nests raided in 2015 on Cumberland Island to just three from 2016 to 2018.”

Likewise, raccoons offer the largest threat due to their persistence, even against screens or other protection. However, researchers say the raccoons are “important members of island food webs and their removal can affect nutrient flow, seed dispersal and other animal dynamics.” They recommend more screening and protection and further study into raccoons, turtle nesting sites and the island’s wildlife dynamics.

Hogs, coyotes and raccoons? Sounds like the axis of evil for sea turtles on Georgia’s islands.

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