During the dry season in southern Africa's Kalahari Desert, there are up to eight months with no rain. Thousands of elephants, buffalo and baboons must migrate to the swamps of the Okavango, a vast inland delta that's at the end of Africa's fourth-largest river.
The long trek is risky. Elephant calves are blinded by the sand and must follow their mothers by sound alone.
As the animals reach the Okavango, so does water. Rain that fell a thousand miles away funnels into the swampy delta. The birds are the first to arrive at the watering hole, but the elephants aren't far behind.