Scientists Measure Secretary Birds’ Ridiculously Powerful Kicks

When Madeleine the secretary bird was hatched at the Hawk Conservancy Trust in England, caretakers thought that he was a she, and he wound up with a girl's name. Prim as that name is, Madeleine can still kick your butt—and now scientists know just how fast and furious his kicks are.

Secretary birds are unusual among birds of prey in that they spend most of their time on the ground and do their hunting on foot. They do their hunting with their feet, too. Their technique for dispatching the small mammals and reptiles they eat is violent, but elegant in its simplicity: They use their long legs, which make them look a bit like eagles on stilts, to kick and stamp their prey’s head until it’s dead—or at least stunned enough to swallow whole.

It’s impressive to watch, and when Steve Portugal was studying some of the Hawk Conservancy Trust’s vultures a few years ago, he sometimes got distracted by Madeleine, who puts on a daily show for visitors by stomping a rubber snake. One of the areas that Portugal’s research focuses on is, as he puts it, the “biomechanics of weird things.”

“I’m interested in the freaks of the animal kingdom, particularly animals that have slightly strange ways of getting about or getting their food,” he says on his webpage. Secretary birds fit that bill, and he decided to take a look at the ins and outs of Madeleine’s fancy footwork.

As they related in a recent study in the journal Current Biology, Portugal and his team hid force-measuring plates around Madeleine’s enclosure and baited him onto them with a rubber snake while filming everything with high-speed cameras. They found that the bird’s kicks come down with a force equal to five times his own 8.5-pound body weight. These blows are not only powerful, they’re also blink-and-you’ll-miss-it fast: Madeleine’s foot was only in contact with the snake for about 15 milliseconds.

Other raptors hit their prey with similar, and even higher, levels of force. Barn owls, for example, can land on rodents with a plummeting strike equal to 14 times their body weight. But that’s a whole owl plummeting out of the night sky—Madeleine and other secretary birds generate their impressive forces from a standstill with just one leg. The walloping might seem like overkill, but there’s a good reason for it. Many of the snakes that secretary birds feed on are venomous, and going after them with a kick that’s weak or slow enough to allow them to fight back could be disastrous for the birds.

Of course, not all their prey is so dangerous. In addition to hunting rubber snakes, Madeleine took an interest in Portugal’s research equipment. Early on in the experiments, the bird spotted the power cables for the force plates and started stomping on those instead of the bait.

Image credit: snowmanradio via Wikimedia Commons // CC BY 2.0