The Serengeti Wildebeest Migration is a massive annual journey of millions of wildebeest, zebra, and gazelle between Tanzania and Kenya. They drop their offspring from January to March, following the promise of rain to the lush Masai Mara grasslands. 
Along the way, they face constant threats from predators. In July, they reach the perilous Mara and Talek rivers, filled with Nile crocodiles. After crossing, they graze in the north for three months before returning to the Serengeti's southern calving grounds. Another movement within Kenya's borders occurs as the herd migrates.