How Do Secretary Birds Hunt Snakes? The Powerful Stomp

Hunting on foot

The secretary bird is the only bird of prey that does almost all of its hunting while walking. A pair leaves its roost tree an hour or two after sunrise and patrols open grassland with long, measured strides, at about 2.5–3 km/h (1.6–1.9 mph). The partners often split up but stay within sight of each other.

As they walk, they scan the ground and stamp on tufts of grass to scare out anything hiding there. Secretary birds are also drawn to grass fires, where they pick off insects, rodents and reptiles fleeing the flames. When an animal breaks cover, the bird chases it at a run, often with its wings half spread, which helps it balance and turn quickly.

The stomp: how a secretary bird kills a snake

Once a snake is cornered, the secretary bird attacks with its feet rather than its bill. It raises one leg and drives the foot down onto the snake, again and again, aiming at the head and neck. A snake that is stunned or has a damaged head cannot strike back effectively, and the bird keeps kicking until the prey stops moving.

Several features make this possible:

• Very long legs. The legs are nearly twice as long as those of other ground birds of similar weight, so the body, neck and eyes stay well above a snake’s striking range.
• Tough scales. The bare lower legs are covered in thick scales, which offer some protection, although the bird depends far more on not being bitten at all.
• Short, stout toes. Secretary birds cannot grasp prey like an eagle; their feet act like hammers.
• Wings and crest. The bird often spreads its wings during a fight. This is widely thought to distract the snake and give it a larger, confusing target, though it has not been tested in detail.

After the kill, the snake is usually swallowed whole through the bird’s wide gape. Larger prey can be held down with one foot and torn apart with the hooked bill.

What the 2016 kick study found

In 2016 a team led by Steven Portugal published a short study in the journal Current Biology on how secretary birds strike. They worked with a trained adult male at a bird of prey center in the United Kingdom, which had learned to attack a rubber snake placed on a force plate, a device that measures the force of an impact.

A contact time of 10–15 milliseconds is far quicker than a human blink, which takes roughly a tenth of a second or more. That is too fast for the bird to adjust its kick by feel once its foot touches the snake. The researchers concluded that secretary birds must rely on excellent eyesight and precise targeting to hit the head before the snake can react. Their long legs, so useful for striking, seem to make them less efficient runners, a trade-off that shows how specialized the stamping technique is.

The authors also suggested that extinct “terror birds” (phorusrhacids) of South America, large flightless predators with a similar build, may once have hunted in a comparable way, although the two groups are not closely related.

Which snakes and other prey do they eat?

Secretary birds take both harmless and venomous snakes, including adders and cobras. The idea that they live mainly on snakes, however, is an old exaggeration. In most areas, snakes are a small share of what they eat.

Their everyday prey includes:

• Grasshoppers, locusts, beetles and wasps
• Mice, rats, gerbils and hares
• Lizards and small tortoises
• Frogs, birds’ eggs and small birds
• Scorpions, spiders, millipedes and freshwater crabs

The stamping method works on all of these. A grasshopper may need only one kick, while a large lizard or snake can take many. Very small items, such as wasps, are picked up directly with the bill.

Is it dangerous for the bird?

Hunting snakes always carries some risk, but secretary birds rarely seem to be harmed. There is no evidence that they are immune to venom. Their safety comes from distance, speed and accuracy: by the time a snake strikes back, it has usually already been hit on the head several times.

Secretary birds are not the only animals that tackle venomous snakes. Mongooses rely on agility, and honey badgers seem to have some resistance to certain venoms (see are honey badgers immune to venom?). Some other birds, such as the kookaburra, kill snakes by bashing them against branches. The secretary bird’s long-legged stamping style, however, is unique among living birds of prey.

Myths about secretary birds and snakes

“They fly up with snakes and drop them.” This is repeated in older books, but the reports are unverified. Kicking on the ground is the method that has been watched and measured.

“They protect themselves with their wings like a shield.” Spreading the wings may distract a snake, but there is no evidence that feathers stop a bite.

“They are the reason South Africa uses the bird as a symbol.” Partly true: the coat of arms of South Africa features a secretary bird, and its snake-killing habit is part of what it symbolizes, namely protection of the nation against its enemies.