A million wildebeest… each one driven by the same ancient rhythm, fulfilling its instinctive role in the inescapable cycle of life: a frenzied three-week bout of territorial conquests and mating; survival of the fittest as 40km (25 mile) long columns plunge through crocodile-infested waters on the annual exodus north; replenishing the species in a brief population explosion that produces more than 8,000 calves daily before the 1,000 km (600 miles) pilgrimage begins again