• Hummingbirds use their feet only to perch or scratch themselves. Moving even a few feet is done by flying.
• Swifts’ legs are almost nonexistent and their tiny clawed feet are suited for little more than clinging to vertical surfaces.
• The legs of some water birds, such as grebes and loons, are set so far back for diving and swimming that walking or even taking off from land isn’t possible.
From Bird Brainteasers