Everything we learn about hummingbirds seems extreme. And here’s the latest news: Scientists at Cornell discovered that hummingbirds are able to exert fairly precise control over the energy they produce in the way of body heat during torpor- a state which is not sleeping and not hibernation, but a kind of brief overnight energy slow down. The discovery showed that hummingbirds – whose lives are lived on a knife-edge of energy – have several stages of torpor. And if humans were to experience even 15% of the same body temperature differences hummingbirds regularly experience in any of these stages, we would suffer rapid hypothermia. So what’s up with hummingbirds?
Hummingbirds have a normal body temperature of 100+ degrees Fahrenheit regardless of the weather. This takes an enormous amount of energy to maintain – especially when the nights are cold. So, to conserve energy, many hummingbirds lower their body temperatures during the night and go into a torpor. Scientists discovered there were three stages of torpor – shallow (where the body temperature of the birds was lowered to about 20 degrees F less than their normal temperature); deep torpor, where their body temperatures were lowered 50 degrees F below their normal daytime body temperature (or nearly cut in half!) and a transitioning state between the two stages of torpor. The smallest hummingbirds seemed to use this latter stage every night and, would often go into deep torpor – which can prove dangerous to the birds, as their immune systems start to shut down and they are very vulnerable to predation and can suffer sleep deprivation.
It turns out 42 species of birds use torpor to conserve energy, but only hummingbirds, nightjars, and one species of mousebird use deep torpor. The more we learn about birds, the more amazing they seem! More detail in this article by Cornell.