The question of whether ducks possess knees often arises because their legs appear to bend in reverse. Ducks, like all birds, do have knees. The confusion stems from the duck’s specialized leg structure, which is adapted for an aquatic lifestyle. This anatomy causes the joints to be positioned and concealed differently than in mammals.
Where the Knee is Hidden
The duck’s knee joint, anatomically called the femorotibial joint, is not externally visible. This joint connects the femur (thigh bone) to the tibiotarsus (the main bone of the lower leg). The femur is relatively short in ducks and positioned high and close to the body.
The entire upper leg, including the femur and the knee joint, is contained within the muscular mass of the duck’s body and covered by feathers. This high placement ensures the knee never protrudes from the body’s silhouette. Consequently, the most prominent, visible joint becomes the focus of attention, often leading observers to mistakenly identify it as the knee.
Identifying the Visible Joints
The large, prominent joint that bends backward is not the knee; it is the hock joint. This joint is the avian equivalent of the human ankle or heel. Officially known as the tarsometatarsal joint, it connects the tibiotarsus (lower leg bone) to the tarsometatarsus (foot bone).
The visible parts of the duck’s leg consist of three main segments. The tibiotarsus extends from the hidden knee down to the hock joint. Below the hock is the tarsometatarsus, a single, fused bone often mistaken for a shin. Finally, the leg ends in the digits and the webbed feet, where the phalanges are located.
Locomotion and Leg Mechanics
The positioning of the duck’s leg structure dictates its movement both on land and in water. The legs are set far apart and far back on the body, which maximizes propulsion efficiency for swimming. This rearward placement forces the duck to compensate for a wide center of gravity when walking.
This wide, rear-set posture results in the characteristic waddling gait. The duck must shift its body weight from side to side with each step to maintain balance, creating a rocking motion. When swimming, the powerful, short legs and large, webbed feet combine with the hock joint’s flexibility to create a strong, paddle-like stroke. The backward bend of the hock allows for a swift recovery stroke by collapsing the foot to reduce drag.