In May the rainy season in the southern Serengeti ends, and herds of zebras numbering in the hundreds of thousands begin to migrate north across the plains from Tanzania up to the Maasai Mara region of Kenya. The herd in our photo today shows a small portion of the 250,000 zebras that will spend the next couple of months or so on the northern leg of their year-long loop across the plains. Joining the zebras will be 1.5 million blue wildebeest that follow the same migratory route. Not every zebra will survive the 500-mile journey. By July the surviving herd will arrive in Kenya’s Maasai Mara, only to leave in November and return to Tanzania.