This is Birdnode.

When it's summer in the Southwest, the call of a common poorwill greets the moon rise.

But in winter, quiet.

The common poorwill doesn't sing much when the mercury drops, but it can do something else that is remarkable.

As the winter cold deepens, this petite member of the night jar family can enter a hibernation-like state and stay like that for hours or even weeks.

Scientists call it torpor.

It happens when an animal slows its body functions to conserve energy and heat.

The bird's heart rate will slow, so does its breathing and body temperature.

Several species of birds can go into brief states of torpor to conserve energy.

Hummingbirds, doves, and the poorwill's close cousin, the Whipperwill.

But the common poorwill is unique in its ability to do so for such prolonged periods of time.

Scientists suspect there may have been an evolutionary advantage for the poorwill if it could stick out the winter instead of migrating.

The poorwill's that stay through the cold come out of their torpor as the temperature rises.

The day's lengthen, insects become abundant again, and the breeding season nears.

And that is something to sing about.

For Birdnough, I'm Michael Stein.