Sandhill Cranes - Platte River Valley, Nebraska. On an early April morning, sandhill cranes leave their roost on a sandbar shortly after sunrise. For four to six weeks in March and early April, half a million sandhill cranes, roughly 80 percent of the world's population, descend upon the Platte River. Here they rest and refuel for a several thousand mile journey from their wintering grounds along the Gulf of Mexico to nesting grounds far to the north. Location: Platte River, Nebraska.