The Common Loon (Gavia immer) is a bird fundamentally adapted for an aquatic existence, spending nearly all of its life on the water and diving to catch fish. Its streamlined body, solid bones, and powerful musculature make it a highly efficient underwater predator. This specialization for a submarine environment, however, has profoundly limited the bird’s ability to move effectively on solid ground. The awkward terrestrial movement of the loon is a direct consequence of its evolutionary trade-offs.
The Limits of Terrestrial Movement
Loons cannot walk upright in the manner of most birds, such as ducks or gulls. Instead, they resort to a clumsy, shuffling movement, pushing themselves forward on their breast and bellies. This movement has been likened to tobogganing or crawling, often using their wings to help balance or propel themselves forward.
Any movement across ground is slow and highly awkward, making them extremely vulnerable to land-based predators. They will not voluntarily travel more than a few feet away from the water’s edge, as this limited mobility makes escape nearly impossible.
Why Loons Cannot Walk Upright
The reason for the loon’s limited terrestrial mobility is purely anatomical, a consequence of extreme adaptation for foot-propelled diving. Their large, webbed feet are positioned far back on the body, near the tail, which is an ideal configuration for synchronous paddling to generate maximum hydrodynamic thrust underwater. This posterior placement effectively turns the legs into powerful, laterally splayed propellers, minimizing drag.
On land, this rearward leg position places the bird’s center of gravity entirely in front of its support structure, making it impossible to swing the legs forward to take a proper step. Furthermore, the loon’s leg structure is highly modified; the main lower leg bone, the tibiotarsus, features a prominent extension called the cnemial crest, which provides a broad attachment point for the massive thigh muscles that power their dives. The legs are also encased in skin and muscle, limiting their flexibility.
Land Use and Nesting Locations
The only instance in a loon’s life where it must come ashore is for breeding, necessitating a highly selective approach to nest placement. Because they cannot walk, loons build their nests immediately adjacent to the water’s edge, minimizing the distance they must crawl to reach the site. The male loon selects a quiet, protected spot, often on small islands or vegetated hummocks, where the risk of predation is lower.
The nest itself is typically a mound of dead plant material built right at the bank, often with a steep drop-off into the water. This arrangement allows the incubating adult to simply slide off the nest and into the water upon sensing danger, providing a rapid escape route from terrestrial threats. The loon’s inability to move across open ground is the primary factor dictating its choice of a waterfront nursery for its eggs and young.