According to a new study published this week in the journal Current Biology, Secretary birds can kick with 195 Newtons, which is equivalent to about 5 times their own body weight, when they kill their prey.
The Secretary bird (Sagittarius serpentarius) is a large terrestrial bird of prey, which stands around 4 feet (1.2 m) tall.It is widespread throughout Africa south of the Sahara.
The single species of its family, the bird gets its name from its crest of long feathers that look like the quill pens 19th century office workers used to tuck behind their ears.
The species is grey, whitish and black in all plumages, with small bill and head, bare face, relatively long neck, exceptionally long, bare legs, and long graduated tail with greatly elongated central rectrices.
It inhabits grasslands, ranging from open plains to lightly wooded savanna, but is also found in agricultural areas and sub-desert. It ranges from sea-level to almost 10,000 feet (3,000 m).
Secretary birds consume snakes, other reptiles, amphibians, tortoises, rats and other small mammals as well as young game birds.
They frequently kick and stamp on the prey’s head until it is killed or incapacitated, particularly when dispatching larger lizards and venomous snakes.
The consequences of a missed strike when hunting venomous snakes can be deadly, so the kicking strikes of secretary birds require fast yet accurate neural control.
The new study, led by Dr. Steve Portugal of Royal Holloway, University of London, focuses on a captive male Secretary bird called Madeleine, held at the Hawk Conservancy Trust, Hampshire.
Madeleine was trained to attack a rubber snake to demonstrate the hunting techniques of this type of bird.
Dr. Portugal and his colleagues from the Royal Veterinary College and the Hawk Conservancy Trust measured Madeleine’s kicks by putting a force plate in the bird’s enclosure and pulling the rubber snake across the force plate.
“The exceptionally rapid strike contact duration is 1/10th of the time it takes to blink an eye – which takes around 150 ms,” Dr. Portugal said.
“Such rapid time, coupled with the exceptionally long legs, means the birds can’t be using proprioreception – the sixth sense we use to sense our position and movement.”
“Therefore, they are using visual targeting and feed-forward motor control during strike events. This means the birds can only correct for a missed strike in the next kick – once they’ve started a kick, they can’t adapt it, and they have to wait for the next strike.”
“Despite their very unusual appearance with exceptionally long legs, the secretary bird’s striding gait is remarkably similar to of ground birds such as pheasants, turkeys and ostriches,” added study co-author Dr. Monica Daley, of the Royal Veterinary College.
“This suggests that specialization for their remarkable kick-hunting technique has not unduly compromised their locomotor abilities.”
Steven J. Portugal et al. 2016. The fast and forceful kicking strike of the secretary bird. Current Biology, vol. 26, no. 2, pR58-R59; doi: 10.1016/j.cub.2015.12.004
This article was first published by Sci-News.com on 26 Jan 2016.