The Harlequin Duck (Histrionicus histrionicus) is a striking sea duck known for its bold plumage and preference for turbulent, fast-moving water. This small diving duck is a carnivore, relying primarily on invertebrates to fuel its active lifestyle. Its diet reflects remarkable adaptability, shifting completely between the coastal marine habitats used during the non-breeding season and the inland mountain streams used for breeding.
Primary Marine Food Sources
Harlequin Ducks spend most of the year in rocky, coastal environments. Their diet here is dominated by hard-shelled, bottom-dwelling invertebrates found in the intertidal and shallow subtidal zones. They specialize in foraging in areas of heavy surf and wave action, environments too rough for many other duck species.
Marine Prey
The primary food items in this marine phase include small mollusks like blue mussels, limpets, and periwinkles, which they pry off rocks. Crustaceans also make up a significant portion of their intake, including amphipods, crabs, and barnacles. Occasionally, they consume small fish or fish eggs, such as herring spawn, when these rich food sources are seasonally available near the shore.
Freshwater and Stream Diet
During the breeding season, Harlequin Ducks move inland to nest along fast-flowing, clear mountain streams and rivers. This transition shifts their diet from hard-shelled marine prey to soft-bodied aquatic insects. The ducks forage by diving to the stream bottom and picking up organisms clinging to or hidden under rocks.
Stream Prey
Their freshwater diet consists mainly of the larval and nymph stages of insects that thrive in highly oxygenated, turbulent water. Common prey includes caddisflies, stoneflies, and black flies, with black fly larvae often representing the highest volume consumed. This insect-heavy diet provides the high protein and energy necessary for successful breeding and growth of their young.
Specialized Diving and Foraging Methods
The Harlequin Duck requires specialized techniques to forage in highly turbulent waters. They are powerful divers, capable of submerging up to 20 meters, though they typically forage in shallower water. Unlike many waterfowl, they use their wings for propulsion while underwater, engaging in “underwater flight” to maneuver against strong currents.
The ducks also employ their bills to probe crevices and the undersides of rocks to dislodge prey in both the pounding surf and swift river currents. They are adapted to maintain their position in conditions that would sweep away other ducks, allowing them to exploit abundant food sources in these current-swept areas.