In 1961, the first photographic census was taken of the wildebeest population. Since then, a photographic census has been taken every two years during the rainy season while all of the migrating wildebeest are in an enormous sprawling herd on the eastern plains.
While flying at set altitudes between 450 and 750 feet, parallel runs are flown over the herd. A radar altimeter is used to maintain a constant altitude while a series of vertical photographs are taken with a 35-millimeter camera mounted on the door of the plane or in a hatch in the floor. Hundreds of photographs are needed to cover the entire herd.
With the aide of a microscope, the animals are counted and pricked with a pen to insure that each animal in the photograph is only counted once.
