The Great Migration is the largest herd movement of animals on the planet. The numbers are astonishing: over 1.5 million wildebeests, zebras, and antelopes move in a constant cycle through the Serengeti-Mara ecosystem in search of nutritious grass and water. Guided by survival instinct, each wildebeest will cover 800 to 1,000 km on its individual journey along age-old migration routes. Hungry predators, including lions, leopards, cheetahs, hyenas, wild dogs, and crocodiles, ensure the strongest survive in this natural spectacle. This is also known as ‘the greatest show on Earth.’ The animals travel from the Ngorongoro Conservation Area in southern Serengeti, Tanzania, through the Serengeti, into the Masai Mara in Kenya, and then back again. The journey is beset with danger: young calves are snatched by predators, the slow ones are brought down by prides of lion, brave beasts break legs on steep river slopes, crocodiles take their share of the stragglers, and the weak and exhausted drown. As for the three major animals of the migrant grazers, they have different grass-eating habits: as one group eats the top of the tallest grass, the next group will eat away some of the medium-height grass until finally it is almost completely eaten, and the herds move on. This means each group sticks to its kind with only a tiny overlap in their distributions. The grasses of the plains have the highest protein content throughout the Serengeti and are also high in calcium. It is unclear how the wildebeests know which way to go. However, it is generally believed that their journey is dictated primarily by their response to the weather. They probably follow the rains and new grass growth. Some experts believe the animals react to lightning and thunderstorms in the distance. It has even been suggested that wildebeest can locate rain more than 50 km away.