They looked like peppercorns ground into the sky and then like ribbons of black silk or a stain spreading overhead.

Each spring, for close to a million years, hundreds of thousands of sandhill cranes converge on the Platte River Valley in central Nebraska. For roughly a month, the birds rest and refuel on their annual path from the southern United States and Mexico, where they winter, to the Arctic regions of Canada, Alaska and Siberia, where they breed. Jane Goodall, who tries to make the trip every year to witness the phenomenon, has called it “without a doubt one of the most spectacular events in the natural world.”

One recent weekend, Sheila Berger, a 65-year-old artist and former fashion model whose own migratory path took her from St. Louis to New York City, assembled a flock of far-flung friends to witness the extravaganza alongside her.

“This viewing rivals any safari you would have in Africa,” said Ms. Berger, whose hat was festooned with a golden frond of grain. “I’ve seen the gorillas in Rwanda, the elephants in Kenya, the lions and wildebeest in Tanzania. This is as good.”