Mara River Crossings

node · earth · Northern Serengeti and Maasai Mara

The mass fording of the Mara River by wildebeest and zebra during the northern phase of the circuit, concentrated between roughly July and October and repeated in both directions as herds oscillate across the river rather than crossing once. Mortality is real and measurable — an average of about 6,250 carcasses and 1,100 tonnes of biomass a year, equivalent to roughly ten blue whales — but it is a small fraction of the migratory population, and the drowned animals form a substantial nutrient subsidy to the river's food web. The crossings are the migration's most photographed moment; they are not the process that sets its population size.