沙丘鹤在长途航行中休息

Every year in the month of March, one of the world's greatest wildlife migrations stops in central Nebraska.

For a short time, sandhill cranes fill the state's wide, flat fields. The land provides these long-legged, playful birds with the perfect place to rest and eat.

Last year, a record 1 million sandhill cranes stopped in the area during their northward migration. That is about 85 percent of the world's sandhill crane population.

In recent years, more and more people have discovered the migration. Visitors crowd into river blinds – special structures that help keep the birdwatchers hidden. They look through their cameras or binoculars in wonder.

Only one other migration on Earth is as concentrated and wondrous, local scientists say. That is the wildebeest migration in Africa.

Getting close to the cranes

One cold morning in the middle of March, travelers gathered before 6 in the morning at Audubon's Rowe Sanctuary here. They walked carefully down a dark path. As the group got closer to the river blind, they began to hear the birds' sounds, or calls.

Naseem Munshi traveled to Nebraska from her home in Colorado to see the cranes. She described the sound the birds make as "such a moving, ancient sound." She added, "If I could just live and breathe that sound, I would be a very happy person."

Munshi and the tens of thousands of other visitors help support the local economy. Last year, people from more than 60 countries came to see the migration.

The cranes -- among the oldest-known bird species -- are worth the trip.

Sandhill cranes are generally a little over a meter tall. They have long legs, necks and beaks. Their wings stretch over two meters.

Sandhill cranes have soft, grey feathers. They are known for having a bright red area on the top of their heads. They are also known for their playful movements. Some call it the cranes' "dance."

The birds stop in Nebraska as they make their way from their winter homes in Mexico and parts of the southern United States. The birds usually spend two to three weeks at this place.

They arrive in waves, at times as many as 400,000 in one day. They eat in the nearby cornfields and grass lands. Leftover grain, insects and small creatures give them the energy they need as they continue their trip north, toward Canada and Siberia.

The cranes appear to float gently through the air. They do not follow any special flying pattern, unlike the ducks and geese that also fill the skies here.

Chris Helzer is science director of the Nature Conservancy in Nebraska. The center gives tours to see the cranes for its members and donors. He describes the way the cranes come down to land as a "dandelion seed falling gently."

For visitors, the most memorable part of their trip happens at sunrise. They gather in the blinds and quietly wait.

As light comes to the river, the birds begin throwing weeds and sticks in the air. They hop, bow to each other and then leap. The movements – or "dancing" -- are all part of pair bonding. Sandhill cranes mate for life.

Helzer said, "You see them waking up after all night on the river; it's gotta be cold. You see them hopping a bit. Then all of a sudden they are jumping in full height and spreading their wings and the morning has started."

Later, thousands of cranes burst into flight. Their collective movement creates a loud, impressive sound.

"It's a very emotional experience for everybody," Munshi said. "Some people cry."

I'm Jill Robbins.

Mike Kilen reported on this story for VOA News. Jill Robbins adapted it for Learning English. Ashley Thompson was the editor.