There are several viewing areas between Grand Island and Kearney, NE. The sandhills migrate through during most of March, but the week of the 25th seems to be the peak for Sandhill Cranes and the following week is the most likely week for rarities (Whooping, Common, etc) but the number of Sandhills are significantly lower. The cranes congregate on the Platte River as the sun sets and stay overnight as long as the water depth is suitable (this year the water was deep and the cranes were displaced more than usual, but it was still very impressive). It is most impressive watching the cranes come in at night, but it is equally enjoyable watching the cranes waking up at sunrise and flying off to the fields. We were there 3 nights and I believe my nightly counts were between 100k-300k cranes every night. There is also a good Greater-Prairie Chicken lek about a half hour north which gives you something to do in the area besides the cranes! If you have any other specific questions I would be happy to answer them off the list-serv (please direct message after this reply).