Just one species of sea snake lives in the open ocean, even giving birth there—yet it can't drink seawater. Scientists have been puzzled at just how the yellow-bellied sea snake survives, National Geographic explains. Now, they've learned that it simply doesn't have to drink for months at a time; in fact, as it gets dehydrated, it can lose some 18% of its body mass, Phys.org reports. To drink, the creature has to wait for fresh water in the form of rain, and that comes only during the rainy season; their natural habitat, off Costa Rica, goes through a dry spell between November and May. "When you scuba dive, you can sort of tell when it's raining," a researcher says. "I think the snakes can, too."
Once freshwater has accumulated above the saltwater, which is heavier, the snake swims up to drink it. It becomes bloated and can then live "in a dehydrated state for possibly six to seven months at a time," notes their paper, published in Proceedings of the Royal Society B: Biological Sciences. Researchers came to this conclusion after capturing some 500 of the sea snakes at different periods during the year. The researchers put the snakes in freshwater tanks and calculated how much they drank by killing them and baking them in ovens, which removed the water they'd stored, Phys.org explains. Those captured during dry periods drank heavily, while those taken during the wet season largely refrained. The snakes' population numbers have been dropping, and it may be because of this dependence on those rainy months; climate change is altering rainfall patterns. (Another snake secret was recently uncovered: How certain species "fly.")