A few weeks ago when I was out cycling with some friends, we saw a few birds who looked like they were sleeping. Someone asked me what they were doing, and I said they were resting or sleeping but I'd ...

Humans do very little when we sleep. This might not seem like a big deal, until you look to the dolphins as they sleep and swim with the pod. Or fur seals, who can sleep while watching out for sharks.

This study was supported by a student grant from the Australasian Society for the Study of Animal Behaviour and a doctoral scholarship from the University of Auckland. Kristal Cain does not work for, ...