Desert nights get cold, and a bird the size of a roadrunner loses heat quickly. Rather than shivering its way through the night, the roadrunner lets its body temperature fall, entering a shallow torpor that cuts its metabolic cost when there is nothing to hunt anyway.
Rewarming by shivering is expensive. Instead the bird uses the sun. It faces away, droops and parts the feathers of the upper back, and reveals darkly pigmented skin along the spine that absorbs solar radiation efficiently. Observers describe the posture as unmistakable, held for many minutes on cool mornings, and it substantially reduces the energy needed to return to normal operating temperature.
The bird's cartoon reputation for outrunning coyotes is the part that misleads. Roadrunners are fast on foot for a bird, in the region of 30 kilometres per hour, but a coyote is comfortably faster, and coyotes do prey on them.