Predators returning to unexpected areas

Brian Silliman adjusted his headlamp. He was searching for crabs and snails in the saltmarshes and creek banks of an island reserve in Georgia. He was studying food webs, using small animals as a model for ecosystem values and predation.

While setting up for his research in the darkness of the night, he suddenly felt like he was being watched. Knee deep in mud, Silliman looked around and spotted a pair of red eyes about 4 feet away. Slowly he made out the shape of an alligator (Alligator mississippiensis).

“I was totally freaked out,” said Silliman, a Rachel Carson professor of Marine Conservation Biology at Duke University. “It lunged at me.”

Silliman was stuck in the mud. He shook a nearby cage that was between him and the alligator to scare gator away. It worked. The gator did a big flip, giving Silliman time to get out of the creek.

“I was freaking out because it shouldn’t have been there,” he said. “It was a fully marine oceanic saltmarsh in a reserve.”

Mustering up his courage, Silliman returned to the area a few days later, where he spotted even more alligators throughout the creek. He tested the water, which turned out to be as salty as the ocean, but alligators are considered freshwater reptiles. “If you see an alligator in the ocean it’s because it was washed out there,” he said. “They’re not supposed to live there, or at least we told ourselves that story.”

Silliman’s encounter got him thinking maybe alligators can, in fact, live in these coastal environments, but humans excluded them through activities such as hunting or development. In a study published in Current Biology, lead author Silliman and his colleagues synthesized data from the literature, government reports and their own data on alligators and sea otters. They found predatory species such as alligators, sea otters (Enhydra lutris), river otters (Lontra Canadensis), gray whales (Eschrichtius robustus), gray wolves (Canis lupus), mountain lions (Puma concolor) and others are now as abundant or even more abundant in “new” habitats than in the ones people expect them to use. But these “new” habitats may actually be areas they once inhabited.

“The best scientists would chalk it up to the aberrant sightings or that these animals are lost,” he said. But Silliman found this isn’t the case. Instead, he suggests the animals were living in refuges, and as a result of conservation efforts and elimination of some hunting, are now returning to the areas where they have been historically. In fact, he said, there’s archeological evidence of alligators in these “unexpected” areas before humans decimated their populations.

Silliman said they also eliminated climate change as the reason for reoccurrences of animals, pointing to the fact that the animals are moving to more stressful habitats, sometimes in warmer areas.

Silliman said this brings to light a few ideas regarding management and conservation of species. One implication is there’s more habitat out there where animals can be placed to recover. For example, biologists may be picking kelp beds for sea otters as habitats they can do best in, when in reality there are many more ecosystems out there that can facilitate their recovery, including river estuaries, where they sometimes appear.

Another management implication is that these animals can help stabilize the ecosystem. While conservationists can spend millions of dollars to rehabilitate the environment, he said, species such as sea otters can be a cheap but important tool for managing ecosystems.

The research suggests humans and wildlife don’t always have to be segregated, Silliman said. People may not appreciate sharing the beaches with alligators, he said, but in many places animals are returning to, humans and wildlife may be able to coexist.

Header Image: An alligator eats a crab, one of its main food sources on coastal habitats. Researchers found many predators are being found in places where they haven’t been seen before such as on beaches or in backyards. ©Brian Silliman/Duke University