The Common Loon (Gavia immer) is an iconic North American waterbird, recognizable by its striking black-and-white breeding plumage and haunting calls that echo across northern lakes. This species is a master of its aquatic environment, displaying grace and speed beneath the surface. The loon’s physical structure is dedicated to a life spent diving and swimming, creating a biological trade-off. This specialization for water leads to a pronounced awkwardness on land, a necessary consequence of its superb diving ability.
The Answer: Terrestrial Movement
The loon can move on land, but its movement is extremely limited and challenging. It does not exhibit the upright, bipedal gait typical of most terrestrial birds. Instead, its locomotion is a clumsy shuffle, slide, or push-and-slide motion with its breast low to the ground.
This ungainly movement means the loon is essentially paralyzed if stranded away from water and must struggle to reach the nearest shoreline. The bird uses its powerful legs to push its body forward, often supplemented by wing-rowing for propulsion. Loons only come ashore for essential activities like nesting, or if sick or injured, spending nearly all other time on the water.
Anatomical Specializations for Aquatic Life
The loon’s terrestrial difficulty is a direct result of its aquatic design, optimized for underwater propulsion. The legs are set extremely far back on the body, positioned perfectly to function like powerful rear-mounted propellers. This posterior placement provides maximum thrust and hydrodynamic efficiency when swimming, but makes balancing the heavy body for upright walking nearly impossible.
Loon bones are denser and more solid than those of most other birds, which typically have hollow, air-filled skeletons. This density helps reduce buoyancy, allowing the bird to dive to greater depths with minimal effort. This added mass, while beneficial for diving, contributes to the difficulty the loon has in supporting its weight on land. The fully webbed feet are large and laterally compressed, generating immense force against the water. Powerful thigh muscles drive these feet, anchored by a prominent extension on the lower leg bone to provide leverage for explosive diving power.
Masters of the Deep: Diving and Swimming Mechanics
Once submerged, the loon transforms into a torpedo-like form, utilizing its specialized anatomy to navigate and hunt. Propulsion is generated solely by the large, webbed feet, which paddle synchronously in a powerful, outward and backward stroke. The legs are also laterally flattened, which minimizes drag and increases the efficiency of movement through the water.
The loon controls its vertical position by manipulating buoyancy. It compresses its feathers to expel trapped air and forces air out of its internal air sacs, allowing it to silently sink below the surface. Loons are visual hunters; their pursuit of fish often involves dives averaging 40 to 45 seconds, though they can reach depths of up to 70 meters. They execute abrupt, tight turns underwater by using one foot as a pivot brake and kicking with the other, a maneuver that helps capture fast-moving prey.
The Necessity of Land: Nesting Behavior
Despite their limitations on solid ground, loons must briefly come ashore to reproduce. This necessity dictates a reproductive strategy that minimizes terrestrial exposure. Nests are built immediately adjacent to the water’s edge, often on small islands, sheltered shorelines, or floating vegetation mats.
This placement allows the loon to slide or push its body onto the nest and quickly slip back into the water if danger approaches. They often select a site with a steep drop-off, enabling them to approach the nest from underwater. While incubating one or two eggs for about 26 to 30 days, parent loons are highly vulnerable to predators and sudden changes in water level. If disturbed, a parent must hurriedly scramble off the nest, sometimes using a panicked shuffle and wing-rowing motion to escape to the safety of the lake.