The Common Loon (Gavia immer) is a distinctive aquatic bird known for its haunting calls echoing across northern lakes and its remarkable diving ability. This species is a specialized predator whose survival depends on its skill in procuring aquatic life in both freshwater breeding grounds and saltwater wintering areas.
The Main Prey: A Diet Built on Fish
The loon’s diet is composed of approximately 80% fish, making them effective top predators in the aquatic food web. They prefer soft-rayed, non-spiny species, which are easier to swallow whole. Freshwater prey commonly includes yellow perch, suckers, minnows, sunfish, and small catfish.
Loons target small to medium-sized fish, typically less than 10 inches long, and consume an estimated two pounds of food daily. They often select fish with erratic swimming patterns, such as pumpkinseed and bluegill, because they are easier to catch than fast, straight-swimming species. Their supplemental diet includes crustaceans like crayfish, aquatic insects, mollusks, and amphibians such as frogs and salamanders.
Specialized Hunting Strategies
Loons possess unique physical adaptations that enable their success as pursuit predators underwater. Unlike most birds, they have solid bones, which helps them overcome buoyancy and allows for deeper, more streamlined dives. They can also compress their feathers and expel air from their air sacs, reducing body volume for a quicker descent.
Propulsion underwater is achieved using their large, webbed feet, which are positioned far back on the body, functioning like a ship’s propeller. Loons typically dive to depths between 13 and 33 feet, though dives to 230 feet have been recorded, and they can remain submerged for over three minutes. Hunting success depends on clear water because loons are visual hunters relying on specialized eyesight to locate prey. Once caught in the spear-like bill, the fish is almost always swallowed head-first and whole while the loon is still underwater.
Variation in Diet: Season and Age
The loon’s diet shifts depending on the season and the bird’s age, reflecting changes in habitat and nutritional needs. During the summer breeding season, adult loons primarily feed on local fish populations in freshwater lakes. When they migrate to coastal areas for the winter, their diet adapts to the saltwater environment.
Wintering loons rely on marine fish like flounder, herring, and rockfish, and they also consume crustaceans such as crabs and shrimp. To manage the higher salt intake from their marine diet, loons possess a specialized salt gland located between their eyes that filters excess salt from their bloodstream.
Loon chicks are initially fed small, easily digestible items by their parents, including small minnows, aquatic insects, and tiny invertebrates. As the young grow, they are gradually introduced to larger fish. Parents continue feeding the chicks until they can hunt effectively on their own, usually around 11 to 12 weeks of age.