Alligators in a North Carolina swamp have been spotted “frozen” with their noses above the ice as temperatures plummeted into the thirties this week.

On Monday, at least 18 American alligators at the Shallotte River Swamp Park in Ocean Isle Beach entered a dormant state called “brumation,” the Associated Press reported. The remained that way through Tuesday, said the park’s manager George Howard.

Brumation is a “semi-shutdown” response seen in cold-blooded animals that allows them to slow their metabolism and go without food, Mother Nature Network wrote last year when Shallotte River Swamp Park reported a similar occurrence—the first time the facility had observed this behavior there.

In alligators, brumation can last from four to five months, and can be triggered by temperatures below 70 degrees Fahrenheit. Alligators have been known to surface before the water freezes, presumably to keep their nostrils above the ice so they can breathe. The process is similar to but different from hibernation, which generally refers to mammals.

The gators can stay locked in the ice for several days, Howard told Mother Nature Network at the time.

“It’s a survival mechanism that they do in the event they need to breathe,” Howard explained. “They stick their noses up out of the water and if it freezes, it will freeze around their snout and still allow them to breathe.”

When the ice melts, Howard said, the alligators simply come free and resume whatever it is they do.