'Ninja eagle' kicks like a mule
25 January 2016 Last updated at 17:02 GMT
UK researchers have completed a mechanical study of the strike of the secretary bird - a large species that lives in sub-Saharan Africa and kicks its prey to death with remarkable agility.
A team from the Royal Veterinary College and Royal Holloway, University of London, studied a male secretary bird housed at the Hawk Conservancy Trust in Hampshire.
Using concealed force pads and a rubber snake, they found the bird's kick delivers a force up to six times its own weight, with a contact time of 15 milliseconds (0.015 seconds) - one-tenth of the blink of an eye.
Lead author of the study, physiologist Dr Steve Portugal, said he often describes the secretary birds as "ninja eagles on stilts".