The spectacle of the annual migration of the Sandhill Cranes is underway as more than a half-million of the big white birds will stop over in western Iowa and eastern Nebraska on their journey from Texas to the Arctic tundra. Paul Johnsgard, a crane expert and a professor at the University of Nebraska, says the Platte River Valley is a perfect pit stop for the feathered long-distance travelers. He says it’s a thrill to see the wide expanse of migrating birds.A popular viewing site is in western Iowa’s Harrison County at the DeSoto Bend National Wildlife Refuge where there’s a large visitor’s center with telescopes. The huge flocks of birds also draw tens of thousands of people to the Grand Island, Nebraska, area every year. Johnsgard says the birds make an admirable and difficult journey, since they don’t have roadmaps or even G-P-S. The start about the middle of February with a few stops along the way in Kansas or Oklahoma. Then stop in Nebraska and head on to the arctic tundra.Johnsgard says the birds’ timing has to be precise — they have to arrive on the arctic tundra just as the snow melts and have just two months to mate and hatch their young before coming back in the fall. He says everyone needs to make the journey to western Iowa or eastern Nebraska to see the mass crane congregation at least once in their lifetimes.This year, National Geographic is installing a crane cam so that you can watch the cranes on its website 24 hours a day. Surf to “http://magma.nationalgeographic.com/ngm/cranecam/”. With regards to another big bird, the number of whooping cranes worldwide fell to about a dozen in the 1930s. Johnsgard led several efforts to save them from extinction. Today there are more than 200 whooping cranes around the globe. They migrate separately and a little later than the Sandhill cranes.