The Arctic Tern is globally recognized for its extraordinary annual migration between the Arctic and Antarctic. This immense travel distance requires an extremely efficient and adaptable feeding strategy. The bird’s diet and hunting behaviors are finely tuned to sustain its high-energy lifestyle across vastly different marine environments.
Primary Food Sources
The majority of the Arctic Tern’s diet consists of small, schooling fish, which provide the high-energy content necessary for breeding and migration. During the Arctic summer breeding season, primary prey items are immature, one-to-two-year-old shoaling species, including capelin, sand lances (sandeels), and the fry of Atlantic herring and cod. These fish are typically six inches or less in length, as the tern’s bill size limits the maximum prey size it can successfully capture and carry.
Marine invertebrates are also a regular and important food source. Arctic Terns consume small crustaceans such as krill, amphipods, and small crabs found near the water’s surface. Krill become much more significant during the non-breeding periods when the birds are far from coastal fishing grounds.
Opportunistic feeding provides variety, especially when the terns are near their coastal or tundra breeding colonies. During this time, they frequently catch terrestrial insects in the air or near the surface of freshwater lagoons. The success of their breeding season remains heavily dependent on the availability of high-calorie fish to feed their chicks.
Foraging Techniques
The Arctic Tern’s hunting strategy is primarily aerial, relying on sharp eyesight to spot prey close to the water surface from a relatively low altitude. The most common method involves “kiting” or a “stepped hover,” where the bird maintains a stationary position against the wind while scanning the water below. Once prey is sighted, the tern executes a rapid, shallow plunge-dive.
These plunge-dives typically immerse the bird to a maximum depth of 50 centimeters (20 inches). The tern’s objective is to snatch fish concentrated near the surface layer of the ocean. They are incapable of deep-water pursuit, which restricts their foraging to the upper water column.
Another technique is a simple “contact dip” maneuver, used to pick up prey right at the water line or to grab insects from the air. The tern is generally a solitary hunter, though groups may form when schools of predatory fish drive smaller prey toward the surface.
Seasonal and Geographic Diet Shifts
The Arctic Tern’s diet changes substantially to match the productivity of its current geographic location. During the Arctic summer, when the terns are focused on rearing their young, their foraging is concentrated near the colony, and their diet is almost exclusively small fish. This fish-heavy intake is necessary to meet the demanding caloric needs of growing chicks.
As the birds embark on their southward migration, their feeding shifts to pelagic zones and open ocean upwellings. Along their migratory route, they utilize highly productive oceanic “stepping stones” like the California Current and the Humboldt Current. In these areas, the diet relies more heavily on small, energy-rich marine invertebrates, particularly krill and copepods, which are abundant in the surface waters of the open ocean.
The wintering period, spent during the Antarctic summer near the edge of the pack ice in the Southern Ocean, also sees a reliance on these small, abundant crustaceans. This dietary flexibility is what sustains the animal on its globe-spanning annual journey.