Not sure if this story is true. Apparently the zebras lead the annual migration and when they get to the Grumeti River where the Nile Crocodiles are waiting, they step aside and graze while the poor wildebeests are forced into the river. Approximately 200,000 - 300,000 wildebeests (mostly young ones)are lost to either crocs or the river each migration. After the wildebeests have finished crossing, then the zebras cross when the crocs already have a full stomach.