The Arctic Tern (Sterna paradisaea) is a seabird known for its extraordinary annual migration between the Arctic and Antarctic. This remarkable feat means the species experiences two summers each year, living in more continuous daylight than any other animal on Earth. Its life cycle is intricately tied to the productivity of polar oceans, allowing it to capitalize on rich feeding grounds.
Main Food Sources
Arctic Terns primarily consume marine organisms, mainly small fish. They seek out immature, shoaling species, typically under 6 inches long, such as sand eels (sandlances), capelin, herring fry, young cod, and smelt. These fish provide dense, high-energy fuel for their active lifestyle and extensive migrations. Consistent availability of these fish is important, especially during the demanding breeding season when parents provision their rapidly growing chicks with nutrient-rich meals.
Beyond fish, marine crustaceans form a substantial part of the Arctic Tern’s diet. Krill, small crabs, and amphipods are common crustaceans consumed, particularly when preferred fish are less abundant or during their Antarctic wintering. Arctic Terns exhibit opportunistic feeding, adapting their diet to the most readily available prey in their diverse environments. This dietary flexibility enables them to exploit a broader spectrum of food items, including mollusks, marine worms, berries, and insects found in their northern breeding grounds. Switching between prey types helps them sustain their considerable energy demands throughout their long annual journey.
Hunting and Feeding Methods
Arctic Terns use distinct aerial hunting techniques, showcasing agility and precision. They hover above the water, often at 30-40 feet, scanning for prey below the surface. Once a target is spotted, they execute a swift, shallow plunge-dive, typically submerging about 20 inches to capture fish. Their dives are precise, allowing them to snatch small, fast-moving prey with efficiency.
Another common feeding strategy is surface dipping, where they lightly touch the water to pick up prey or pluck insects from the surface or mid-air. Their keen eyesight helps detect subtle movements of fish from above the water. The Arctic Tern’s specialized beak, pointed and often bright red or orange during breeding, is well-suited for grasping and holding slippery fish. Some terns have fine serrations inside their upper bill, aiding in securing aquatic catch.
Seasonal and Regional Dietary Shifts
The diet of Arctic Terns varies depending on season, geographic location, and prey availability. During the breeding season in the Arctic, fish are paramount; parents require a consistent supply of high-quality, lipid-rich fish to feed their rapidly growing chicks. A scarcity of these preferred fish can directly lead to reduced fledging success for the young. Males often provide more food to the female during courtship and to the chicks after hatching.
As they embark on their extensive annual migration, Arctic Terns become more opportunistic, consuming small marine life abundant in the oceans they traverse. For instance, while wintering in the Antarctic, krill and larger zooplankton often become a more prominent part of their diet, especially near the productive pack ice. Environmental factors, such as changing ocean currents, sea ice extent, and climate patterns, influence prey distribution and abundance, impacting their foraging success and dietary composition across their vast range.