Tanzania's elephant catastrophe: 'We recalculated about 1,000 times because we didn't believe what we were seeing'

Elephants in the Ngorongoro Crater, Tanzania Photo: Copyright (c) 2014 Rex Features. No use without permission. As Howard Frederick flew in a Cessna low over the scrubland of Tanzania’s Selous game reserve, it was the complete absence of elephants rather than the piles of scattered bones he saw that chilled him most.