Joel Sartore's migratory birds

Though it's been studied for decades, the astounding precision of bird migration is still fundamentally mysterious and unknown.

National Geographic photographer Joel Sartore documents birds making their annual migrations north -- comets of color that splash across the landscape in Spring.

Left: Sandhill Cranes flying over the Platte River in Nebraska.

Goldfinches, grackles, red-headed woodpeckers (left) -- these visitors to the woodlots, pastures, marshes and suburbs of Nebraska aren't strangers; they're most likely the same old friends from last year, and the year before.

Many have just flown in from South America. How do they do it? We haven't got a clue.

We understand that long-lived birds, like cranes, learn landmarks along their migratory routes from their parents, and that other species find their way using the angle of the sun, or the stars, or the Earth's magnetic field. But that's about all we understand.

Left: A Whooping Crane (Grus americana) and chick.

Left: A Boblink (Dolichonyx oryzivorus) with a geolocator on its back to track its migratory route.

A male Painted Bunting (Passerina ciris), a species of the Cardinal family.

The Eastern Bluebird (Sialia sialis).

Baltimore Orioles (Icterus galbula) near Raymond, Neb.

The American Robin (Turdus migratorius), a migratory songbird.

An American Robin's nest, with hatched eggs.

Left: The Prothonotary Warbler (Protonotaria citrea).

Biologists think warblers may have a celestial chart in their heads to navigate by - or, rather, a double map, because the stars are different in Spring than in Fall.

Sandhill Cranes (Grus canadensis).

Migratory Sandhill Cranes roost at the National Audubon Society's Rowe Bird Sanctuary, at Gibbon, Neb.

National Audubon Society's Rowe Bird Sanctuary, at Gibbon, Neb., is comprised of nearly 1,900 acres along the Platte River.

Students observe bird life at the Rowe Bird Sanctuary, in Gibbon, Neb.

The Piping Plover (Charadrius melodus).

A Whooping Crane hatches.

Whooping Crane chicks (Grus americana).

At the end of the nesting season, at just eight weeks old, the Cliff Swallow (Petrochelidon pyrrhonota) picks up and flies, on its own, to an exact spot in Argentina, thousands of miles away.

Goldfinches.

An endangered Least Tern with chick (Sternula antillarum).

Newly-hatched Least Tern chicks (Sternula antillarum).

Least Tern with chicks (Sternula antillarum).

White Pelicans (Pelecanus erythrorhynchos).

The Red-winged Blackbird (Agelaius phoeniceus).

A young girl birdwatching along the Steamboat Trace Trail, between Peru and Nebraska City, Neb.

For more info:
joelsartore.com
nationalgeographic.com
"Let's Be Reasonable" by Joel Sartore
photoark.com
National Audubon Society's Rowe Sanctuary, Gibbon, Neb.

By CBSNews.com senior editor David Morgan