Common poorwill
Based on Wikipedia: Common poorwill
The Bird That Sleeps Through Winter
There's a small, unassuming bird in the American West that does something no other bird on Earth is known to do. It hibernates.
The common poorwill—a mottled gray creature barely larger than your fist—can slow its metabolism to nearly nothing, tuck itself into a rocky crevice, and remain essentially unconscious for weeks or even months at a time. Its body temperature drops. Its breathing becomes imperceptible. To all appearances, it might as well be dead.
This isn't the brief torpor that hummingbirds enter on cold nights, waking at dawn to resume their frenetic lives. This is something far more profound—the closest thing to true hibernation found anywhere in the bird world.
What Exactly Is Torpor?
To understand why the poorwill's behavior is so remarkable, we need to understand what torpor actually is, and how it differs from sleep.
When you sleep, your body temperature stays roughly constant. Your heart keeps beating at a reasonable pace. Your brain cycles through various stages of activity. You can be woken up fairly easily.
Torpor is different. It's a controlled shutdown. The animal's metabolic rate—the speed at which its body burns fuel—drops dramatically. Body temperature plummets, sometimes to just a few degrees above freezing. Heart rate slows to a fraction of normal. The creature becomes, in essence, barely alive.
Many small mammals hibernate this way: ground squirrels, marmots, certain bats. They survive winter by simply turning themselves off. But birds? Birds are supposed to be different. Their bodies run hot and fast. They migrate thousands of miles rather than face the cold. They don't hibernate.
Except the poorwill does.
Discovery in the Desert
The scientific confirmation of this extraordinary ability came in the winter of 1946-1947, thanks to a biologist named Edmund Jaeger and a chance encounter in California's Chuckwalla Mountains.
Jaeger found a poorwill wedged into a small crevice in a rocky canyon wall. The bird appeared dead—completely unresponsive, cold to the touch. But when Jaeger returned days later, the bird was still there, still in the same position. He came back again and again over the following weeks. The bird never moved.
Then, as the weather warmed, the poorwill stirred. It blinked. It flew away.
Jaeger had witnessed something ornithologists had speculated about for centuries but never confirmed: a bird in true extended torpor. He published his findings in 1948, and the poorwill became famous—at least among people who care about such things.
But the Hopi Knew First
Science often "discovers" what indigenous peoples have known for generations, and this is no exception.
The Hopi people of the American Southwest have a name for the common poorwill: hölchko. It translates to "The Sleeping One."
They knew. They'd always known. Long before Edmund Jaeger scrambled up that rocky slope in the Chuckwalla Mountains, the Hopi had observed these birds entering their deathlike slumber and returning to life when the world warmed again.
Even Meriwether Lewis—of Lewis and Clark fame—recorded observations of hibernating poorwills during the expedition's 1804 passage through North Dakota. But his notes were largely ignored. At the time, scientists didn't even recognize the common poorwill as a distinct species; they thought it was just another whip-poor-will, the closely related bird common in eastern forests. The significance of what Lewis saw went unappreciated for over a century.
A Bird Named for Its Voice
If you've spent time in the western wilderness at night, you may have heard a poorwill without knowing it. The bird's name is onomatopoeia—an imitation of its call.
Poor-will.
Two syllables, repeated endlessly from dusk until dawn. If you're close enough, you might catch a third, quieter syllable: poor-will-low. It's a monotonous sound, almost hypnotic, drifting across the dry scrublands and rocky slopes where these birds make their homes.
The poorwill belongs to a family called the nightjars—nocturnal birds found around the world, all of them cryptically colored, all of them insect-hunters, most of them named for their strange calls. The whip-poor-will. The chuck-will's-widow. The European nightjar.
The scientific name tells its own story. Phalaenoptilus nuttallii. The genus name comes from Greek: phalaina, meaning moth, and ptilon, meaning feather or plumage. Moth-feathered. It's a poetic way of describing the bird's soft, mottled appearance—camouflage so effective that a poorwill resting on rocky ground becomes nearly invisible.
The species name honors Thomas Nuttall, a nineteenth-century naturalist and friend of John James Audubon. Audubon himself first formally described the bird in 1844, working from a specimen collected along the Missouri River in what is now South Dakota.
The Smallest Nightjar in North America
At about eighteen centimeters long—roughly seven inches—the common poorwill is the smallest member of its family in North America. It weighs between thirty-six and fifty-eight grams, which is to say somewhere between the weight of six or seven quarters and a small deck of playing cards.
Both males and females wear the same gray-and-black patterned plumage, though males have slightly more prominent white tips on their outer tail feathers. The overall effect is of a bird designed to disappear—to blend into the rocky, arid landscapes it calls home.
You can distinguish a poorwill from other nightjars by its size (smaller), its wings (rounded, with tips that reach the end of its short tail when at rest), and its overall coloration (pale gray rather than brown). But honestly, you're unlikely to get a good look. These are creatures of the night, and they're very, very good at not being seen.
Where the Poorwills Live
The common poorwill ranges across much of western North America, from British Columbia and southeastern Alberta in Canada down through the western United States and into northern Mexico. They favor dry, open country—sagebrush flats, rocky hillsides, desert scrubland, anywhere with enough bare ground for them to rest and enough insects to sustain them.
They're not picky about vegetation, or rather, they're picky in the opposite direction. Too many plants, and they can't do their thing. They need openness. They need rocks.
Northern populations migrate south for winter, though "south" is relative—many simply shift to the warmer parts of their existing range in Mexico and the southwestern United States. And some don't migrate at all. Those are the ones that hibernate.
Currently, scientists recognize six subspecies, each adapted to slightly different conditions across this vast range. There's the dusky poorwill of coastal California, darker and browner than its relatives. The desert poorwill of the Sonoran Desert, paler to match its bleached surroundings. The tiny San Ignacio poorwill of southern Baja California. Each one a subtle variation on the same successful theme.
Hunting in the Dark
Like all nightjars, the common poorwill is an insectivore—a hunter of moths, beetles, grasshoppers, and whatever other invertebrates venture out after sunset.
Their hunting technique is distinctive. Rather than hawking insects on the wing like a swift or swallow, poorwills often hunt from the ground. They'll sit motionless on a patch of bare earth or a low rock, watching the darkness with their enormous eyes. When prey comes within range, they leap—a sudden vertical explosion into the air, mouth agape, snatching the insect and returning to their perch in one fluid motion.
They also drink on the wing, skimming low over water and sipping without landing, like tiny feathered aircraft refueling in flight.
The indigestible parts of their prey—the chitinous exoskeletons, the hard wing cases—are regurgitated as pellets, much like an owl casts up the bones and fur of its rodent meals. If you find a poorwill's roosting spot, you might find a collection of these pellets below, compressed wads of insect debris marking a successful hunter's territory.
Nesting on Bare Ground
The poorwill's approach to nesting is minimalist in the extreme. There is no nest, really—just a shallow scrape in the dirt, often at the base of a slope, sometimes partly shaded by a bush or grass clump. That's it. No construction. No gathering of materials. Just earth.
Into this scrape, the female deposits typically two eggs—white or creamy or pale pink, sometimes faintly mottled with darker spots. Both parents share incubation duties over the next three weeks. When the chicks hatch, they're semiprecocial, meaning they're covered in down and can move around almost immediately, though they still depend on their parents for food.
Fledging takes another three weeks or so. Usually there's just one brood per year, but sometimes females get ambitious. They'll lay a second clutch at a new site, up to a hundred meters from the first, and incubate it themselves while the male continues feeding the first batch of young. A logistically complex arrangement for a bird with a brain the size of a pea.
If you stumble upon an incubating poorwill—which is unlikely, given their camouflage—you might witness a remarkable defensive display. The bird will tumble off the nest, open its mouth wide, and hiss. The effect, apparently, is meant to suggest a snake. Whether it actually fools predators is unclear, but it's certainly startling to the occasional human interloper.
The Mystery of Bird Hibernation
Why don't other birds hibernate? It's a question that makes the poorwill even more fascinating.
The standard explanation involves the physics of flight. Flying is extraordinarily energy-intensive. Birds maintain high body temperatures and fast metabolisms because they need to—their muscles must be ready to generate explosive power at a moment's notice. Letting all that cool down, the theory goes, is too risky. A hibernating bird woken by a predator couldn't fly away fast enough to escape.
But the poorwill has found a workaround. It hides.
By wedging itself deep into rock crevices and boulder piles, the poorwill reduces its predation risk to nearly zero. Nothing can get to it. So it can afford to shut down completely, waiting out the cold months in a state that would be suicidal for a bird that needed to flee.
It's also worth noting that the poorwill lives in places where winters are cold but not devastating—the southern edges of deserts, the rocky foothills where temperatures drop but don't plummet. A poorwill trying this trick in Minnesota would freeze solid. But in the Chuckwalla Mountains? The math works out.
Names and Legacy
The common poorwill's scientific journey reflects the broader history of American ornithology. First collected and described during the great era of biological exploration in the mid-1800s, it was initially lumped with related species before being recognized as distinct. Audubon named it. Ridgway gave it its own genus. Jaeger revealed its most remarkable secret.
And all along, the Hopi knew it as The Sleeping One.
There's something satisfying about that arc—the way local knowledge, scientific observation, and careful research eventually converge on the same truth. The poorwill hibernates. It always has. We just took a while to officially notice.
Finding a Poorwill
If you want to see one of these birds for yourself, your best bet is a warm evening in the western United States, somewhere dry and rocky. Listen for the call at dusk. Scan the ground with a flashlight—their eyes shine red in artificial light, a phenomenon called eyeshine caused by a reflective layer behind the retina.
You probably won't see one on your first try. Or your tenth. These are secretive creatures, masters of concealment, active only in darkness. But if you're patient, and lucky, you might glimpse a small gray shape fluttering up from the desert floor, snatching a moth from the air, and settling back to earth as silently as it rose.
And if you're very lucky indeed, you might find one in winter, cold and still in its rocky hiding place, dreaming whatever dreams a hibernating bird might dream, waiting for the world to warm again.