Birds' legs and feet
Birds' legs and feet have adapted to suit many different lifestyles.
How birds' legs have adapted
A bird's leg bones tend to be heavier than a similar-sized mammal's. This is because a bird has just two legs to stand on, so they must be strong enough to support its entire weight, whereas most mammals use four.
Although birds' knees seem to bend backwards, they don’t. We cannot see their knees. What we see is the ankle. Their knees are much further up, usually obscured by feathers. Below their ankles is their foot, meaning that birds stand on their tiptoes. This also helps with their balance.
Killing and carrying
Eagles kill their prey with their feet. Their legs have to be strong enough to take the impact, and to carry the prey back to the nest. The thick feathers on an eagle’s belly hide the full length of its legs. But you can see on its skeleton that they are surprisingly long.
Wading birds use their long legs to enter deep water, whilst keeping their body above the surface to look for food. Stilts have enormously long legs, which help them to find food that other wading birds of their size can’t reach. Long-legged birds often perch on one leg while resting, helping to keep them warm as long legs lose heat rapidly.
Ostriches have even bigger, heavier legs than us. They have no need to save weight, since they are flightless. Instead, they get around by running. An ostrich can run at 70 kilometres per hour, faster than many birds can fly. At full speed, it takes strides of over four metres.
Swifts have virtually no legs, just tiny toes for clinging to the cliffs and buildings where they nest. They sleep, feed and mate in the air, and never intentionally land on the ground. As they don’t need legs they have adapted not to have them.
How birds use their feet
Most birds use their feet for walking or perching, but feet can be weapons (owls), paddles (ducks), and hands (parrots). Feet are also vital for scratching; how else could a bird reach its head?
Most birds have four toes, with three facing forward and one back, but some birds’ toes are adapted to suit different needs. Woodpeckers, for example, have two set forward and two back, to brace themselves firmly against a vertical tree-trunk. Many game birds, and domestic chickens, have a fifth toe with a sharp claw that they use for fighting rivals.
The feet of raptors and owls are called talons. Their sharp claws can pierce the skin or skull of their prey and hold it down while tearing off the flesh. The secretary bird is a tall raptor that hunts on the African savannah. The soles of its feet have tough pads of skin, which it uses to stamp on prey such as snakes and rodents.
Ducks, cormorants and many other swimming birds have webbed feet. They work like paddles to push against the water and propel the bird along. The toes fold up out of the way as each leg swings forward, just like a rower raising an oar out of the water before pushing back again.
Walking on water
Many marshland birds, such as moorhens and herons, have long toes that spread the bird’s weight. This helps to stop it sinking into the mud. The longest toes of all belong to the tropical jacana, which can walk across lily pads and other floating vegetation.
Ever wondered why birds never fall off their perch? The answer is in their feet, which automatically grip tightly when their bodies are at rest. This is because the tendons that flex the toes run along the outside of the ankle and knee, so the toes clench when these joints bend.