Like us humans, birds are bipedal, walk or stand on two legs. Look at any image of a bird and you will notice the most visible joint pivots like our ankle. What we see as the birds’ leg is really its foot. Nature uses a basic structure over and over; this is called homologous structure. When you see a standing bird, it is not standing on its foot, but on its toes.
While the leg structure is universal in birds, the toes or what we call their feet have special adaptations to facilitate their survival.
A bird that feeds on the branches of a tree needs toes that wrap around the branch and hold tight. Their back facing hallux (homologous to our big toe) provides that grip. This three forward and one back toe arrangement is called anisodactyl. Most passerine species are anisodactyl (swifts are an exception). If you look at a field guide arranged in evolutionary order as most are, the Passerines are every species from flycatchers on.
Want to grab onto the trunk of a tree like a woodpecker? Have two toes forward and two toes back (zygodactyl), creating a more stable platform. Parrots, owls, and osprey also have this toe formation, though one of those back toes can be pivoted forward.
Life in the water creates different challenges. To enhance our swimming, we can put on flippers. This generates a longer wider foot enabling a swimmer to push against more water. Our legs stick out behind us when we swim. Birds’ legs dangle. A solid flipper like we use would be a challenge as the same amount of force would be in the forward stroke as in the backward stroke, limiting motion. Waterbirds solve this problem in multiple ways. The webbed toes of a duck is one solution. To reduce the resistance of the forward stroke, the bird closes its toes, so the webbing does not create drag. Birds with webbed feet include all the ducks, gulls, penguins, and all seabirds like loons, terns, cormorants, petrels, albatrosses, gannets, and frigatebirds to name a few. Palmation is the scientific term for the webbing.
Some water birds solved the problem of drag not with webbed toes, but with flexible flaps or lobes that fold back on the forward stroke and flap open on the back stroke. Birds like this are grebes, coots, and phalaropes.
Besides Passerines, many other birds have an anisodactyl arrangement. Gamebirds like chickens, turkeys, grouse, and quail have that back toe raised higher on the body to use as a weapon. Water birds and shorebirds often have that back toe greatly reduced in size. The long toes of shorebirds enable them to move around in the water and mud. Birds like the Semipalmated Sandpiper or Semipalmated Plover, have some webbing between their toes.
Raptors, hawks except for Osprey, are anisodactyl, but the feet are extra heavy, strong, and sharped taloned to serve as killing machines.
Bird feet and legs are truly amazing adaptations that help birds to thrive in a wide variety of habitats. By understanding the different types of bird feet and legs, we can better appreciate the diversity of these amazing creatures.
Of course, bird feet are not the only feature that can be used to determine species. Other features, such as plumage, beak shape, and size, are also important. However, bird feet can be a very helpful tool for bird identification. Next time you bird, pay attention to the “feet” and look for the various arrangements and spend some time thinking about how those feet help the bird survive.
Here are some additional tips for using bird feet to determine species:
• Pay attention to the shape and size of the bird’s toes.
• Look for the presence of webbing or other features.
• Consider the bird’s habitat and lifestyle.
• Compare the bird’s feet to field guides or other resources.
With practice, you will be able to use bird feet to identify a wide variety of bird species.
Submitted by: Bob Mercer
Photos: Bob Mercer