The greatest concentration of cranes can be found in the 50-mile stretch of river between Grand Island and Kearney, Nebraska. Hundreds of thousands of sandhill cranes descend on the area each year between the beginning of March and mid April. They also pass through the area during their fall southward migration, but they don't stay nearly as long in the fall as they do in the spring, so your best bet is visiting in the spring. I visited in mid March.
I spent the rest of the afternoon driving around the back roads looking for cranes, and finding quite a few groups. Groups seemed to range in size from around 20 or so to as many as 150 in one place. I had more luck finding them south of the river than I did on the north side, but I never had to drive too far to find another group of them wandering around a field. About an hour or two before sunset I made my way back to the river, which is where the real spectacle would begin.
I chose to take the evening footbridge tour from the Nebraska Nature Visitor Center, which was well worth the $15 cost! They also offer viewing blind tours for only $25, which take you to a small concealed structure on the riverbank that gets you even closer to the cranes.
I left the Visitor Center before sunset with the other 20 or so people in the tour group. You have to arrive at the footbridge over the river before the cranes do so that they don't get spooked by the large group of people. We only had to wait on the bridge for about 30 minutes before it started to get dark and the first group of cranes arrived. They landed first in the field on one side of the river, but eventually a few of them flew over the brush on the riverbank to the sandbars in the middle of the river. Soon enough another group of cranes arrived, then another and another. Many of them landed in the field first before venturing into the river, but others went directly to the sandbars. Some groups even flew over our heads on the bridge before landing in the river. Eventually two of the sandbars were completely filled with cranes, who were enthusiastically squawking at each other. Their calls are a bit strange sounding. It's hard to describe, but I've included a handy video below so you can hear them too! The cranes in the video are only about a tenth of the cranes that ended up roosting here, but unfortunately the fading light made photography pretty much impossible after a while.
My visit to the Platte River was a truly magical experience. Up until a few years ago I had no idea that such a massive animal migration even existed in the US. Growing up in a city, I thought stuff like this could only be seen in far off places like Africa or Asia. But amazing natural marvels like this can be found in all parts of the world if you know where to look.