Imagine for a moment that you’re a sea snake and you’re feeling a little chilly. That’s quite understandable for an ectotherm. Your body temperature rises and falls with that of your environment, and spending all day slither-swimming through the water can wick away your precious body heat.

You could bask in the sun to remedy the cold. That’s a classic reptile way of working some warmth back beneath those scales. But there’s another option. You could steal your warmth. All you’d have to do is find some seabirds.

There’s a specific term for this warmth-sucking behavior – kleptothermy. The conditions, laid out by François Brischoux and colleagues, are really quite simple. There has to be a warm animal in a relatively cool