iain douglas hamilton is a leading authority on elephants. he is based in nairobi and he says there has been another spike in elephant poaching recently. >> in 2011 we estimated there were 40,000 elephants illegally killed. if that rate were to continue it would inevitable drive the elephants down, because they cannot reproduce fast enough to replace the losses caused by natural mortality and illegal killing for ivory combined. >> reporter: hamilton is one of nearly 50 conservationists across africa supporting the great elephant census. >> you can't fight a war to save something if you don't know how many you are trying to save. >> so to have this foundational information on precisely how many elephants are left will help gauge future conservation efforts. >> reporter: it is an enormous challenge, elephants are found in 37 african nations. populations vary in size, but some countries refused to take part in the survey. >> and that for me has been the most difficult part of the great elephant census to comprehend why people, why countries don'