Just before sunrise, in the hourglass heart of the North American continent, the temperature has dipped to 15 degrees on the Platte River near Kearney, Neb.

I’m shivering in a wooden blind, even with layers of fleece and foot warmers to ward off frostbite. It’s late March and it shouldn’t be this cold, not even in the Great Plains. Across the frozen landscape, the sun begins its ascent into a blush-colored sky and slowly dark shapes on the river begin to stand and stretch and flap.

An ancient, natural avian spectacle is about to happen here at the Rowe Sanctuary. The sandhill cranes are awakening, untold thousands of them, their silhouettes barely visible in the bitter predawn cold. From the mist, a cacophony of cackles, calls and coos rises with each passing minute, the cadence increasing with daylight.

For the cranes, waking from a cold night on the silent, swiftly running river, sunrise brings feeding time. Up to a half-million birds will rise and fatten up on waste corn, most of it leftover from autumn harvest months earlier, in the vast acreage of fields, open landscapes and pastures of rich, sweet grass before returning back to the river at sunset to slumber again.

During that time, the cranes will look for a mate, striking poses, bending and preening for a few moments of passion on the prairie. For the nosey birdwatcher — that would be me — it’s worth a 15-degree morning to see the spectacle of the cranes searching for a mate for life.

Flock takes off as one

I’m in Nebraska to see the annual migration of the cranes passing through the Platte River Valley from their wintering grounds in Texas and Mexico as they glide north to Canada and Siberia for the breeding season. I’m in the blind — a shed, really — anticipating the massive breakfast liftoff that will soon occur.

That surreal moment comes sooner than I expect. A pair of scalawag eagles have caused havoc among the birds, and suddenly, seemingly impenetrable synchronized clouds of blue-gray cranes lift to the skies in a furious attempt to escape becoming the predators’ next meal.

The eagles dive into the mass of birds, with flocks of cranes going every which way. The bright early morning sun is occluded by the wing-tracks of 10,000, 20,000, 30,000 birds.

And just like that, they are gone for the day, only to return late in the evening, when long stretches of V-shaped columns of birds come in like a never-ending freight train.

About 70,000 cranes zip through the Rowe-Kearney area each night during migration along the Central Flyway, one of four routes across the United States that most birds — waterfowl like ducks and geese, and more than 300 other species, including the stately heron — follow annually.

The birds stay in the Platte River Valley for about three or four weeks, consuming enough calories to bulk up, increasing their body weight by about 20 percent for the lengthy flights north.

Earlier in the day, a ghostly field of snow geese, probably a bit of a nuisance to the Midwesterner, is a magical occurrence to a Southerner like me.

The migration is amazing. The cranes are huge, 5 feet tall with gray plumage, sporty red caps and some serious attitude. Their wingspan easily reaches 6 feet, enough to give you a beating should one get hold of you. Not to worry. You can’t come within a country mile of one of these skittish babies.

Sometimes you’ll see whooping cranes, that rarest and most beautiful bird, as they follow the migration route, too. In another early morning jaunt to the Crane Trust Nature and Visitor Center, jumbled into the racket of sandhill cranes we hear a single-engine airplane.

As the plane comes into sight, Brad Mellema, once director of the Crane Trust, speaks in a low whisper so as to not disturb the jittery birds. “If it circles, that means they’ve sighted a whooping crane.”

I was a bit disappointed as the plane puttered on westward, signaling the whoopers were nowhere to be found.

All in all, the sandhill cranes gave a five-star performance.

“Cranes have been moving up and down this highway for centuries,” says renowned nature photographer and author Michael Forsberg. “They’ve seen the rise and fall of civilizations.”

The prairie chicken dance

Like those who travel to East Africa for the Great Wildebeest Migration of Kenya and Tanzania, birdwatchers flock from all over the world to climb aboard the crane train that begins in late February and lasts until April. Peak times are about the last two weeks in March.

“It’s a place where you have to linger,” says Forsberg. “The more you stay here, the more you want to stay. It’s not just a great gathering of birds but a great gathering of people.”

And a great gathering of prairie chickens in a lek. Don’t let the word scare you. A lek is Swedish for crazy chicken mating on the wide open prairie, or something to that effect. A lek is just a gathering of birds, and to see them dance — puffing up, strutting, stomping, dancing and singing under the wide open prairie — is just Plains fun.

“The prairie chickens are no more a chicken than anything,” explains Mellema. “They are a grouse.”

Grouse or chicken, the sounds are amplified and you can hear every peep and flutter for miles around.

The Rowe Sanctuary can arrange a birding trip for you, but you have to be up at the crack of dawn, as the early prairie chicken bird gets the corn.

I’m not a bird expert by a long shot, only a lifelong admirer of all winged creatures, great and small. Perhaps, like me, you’ll come away from what National Geographic calls the greatest wildlife phenomenon in the country all insane for cranes.