The arctic tern (Sterna paradisaea) is a medium-sized seabird that breeds in the Arctic and subarctic regions. During the northern summer, arctic terns live in Arctic and subarctic coastal tundra habitats near marshes, lakes, and shorelines. In the winter, they migrate long distances to Antarctic and subantarctic oceans. The arctic tern has the longest migration of any bird, traveling up to 44,000 miles roundtrip each year. Their Arctic breeding and Antarctic wintering habitats present the birds with extremely different environmental conditions.
Arctic Breeding Habitat
Arctic terns nest in colonies on the tundra of the far north. Their breeding range includes northern parts of Europe, Asia, and North America above roughly 60° north latitude. Some of the key characteristics of their arctic breeding habitat include:
- Location above the tree line in the low Arctic tundra
- Coastal areas near marshes, lakes, ponds, and shorelines
- Low-growing vegetation like grasses, sedges, and heath
- Relatively high density of aquatic insects, small fish, and invertebrates to feed on
- Snow and ice cover the ground for much of the year
- Low species diversity compared to temperate regions
- Summer temperatures typically range from around freezing to 50-60°F
- Natural shelters like rock outcrops help protect nests from cold winds
The open, treeless tundra provides good visibility for spotting aerial and ground predators. Arctic terns nest in shallow scrapes lined with grasses, lichens, and moss. They tend to nest in colonies ranging from just a few dozen to over 2,000 pairs of birds. Colony sites are typically on slightly elevated gravel areas near water, which reduces risk of flooding. The terns aggressively defend their nesting territories from predators and intrusions by other terns. Despite the challenges of the harsh arctic climate, the long days of constant daylight in the Arctic summer provide ample time for hunting fish, courtship, and raising chicks.
Antarctic Winter Habitat
After breeding and raising chicks in the Arctic, arctic terns undertake an immense journey to reach their Antarctic wintering grounds. They fly down narrow migratory routes mainly over the Atlantic Ocean to reach Antarctica and the surrounding Southern Ocean waters. Key aspects of their Antarctic marine habitat in the austral summer include:
- Ice-free coastal waters and zones around offshore islands
- Areas of upwelling that bring nutrients and marine prey to the surface
- Water temperatures around freezing to 40°F
- Long hours of daylight even during the austral summer
- Highly productive marine food chains
- Few aerial predators like skuas and giant petrels
The arctic terns remain on the wing during their entire time in Antarctic waters. They fly and float on the ocean surface while hunting fish, krill, and squid. Their plumage is well-adapted to repel water and provide insulation from the cold air and water. Although Antarctic seas may seem inhospitable to humans, they provide a rich source of food and safety from predators for arctic terns. After several months feeding at sea, the birds make the return migration back to the Arctic to breed in spring and summer.
Unique Adaptations
Arctic terns possess many specialized adaptations that allow them to thrive in both extreme polar environments:
Morphology
- Streamlined body shape reduces drag during flight
- Long, narrow wings provide speed and endurance for lengthy migrations
- Pointed bills catch fish and other prey
- Webbed feet aid swimming on ocean surface
- Water-resistant plumage stays dry and insulated in cold water
- White undersides camouflage terns against the sky from below
- Black caps reduce glare from sun and water
Physiology
- High metabolism generates internal heat
- Efficient oxygen uptake sustains long flights
- Salt excretion keeps salt load in balance while living at sea
- Fat storage provides energy for marathon migrations
Behavior
- Foraging strategies maximize prey capture in both environments
- Aggression defends nesting territories and colonies
- Annual migratory cycle connects polar habitats
- Social flocking reduces risk from predators
This combination of adaptations allows arctic terns to nest, feed, migrate, and raise offspring under the dramatically different conditions found across the Arctic and Antarctic.
Breeding Behavior
During the summer breeding season, arctic terns display a fascinating array of courtship, territorial, nesting, and parenting behaviors. Some highlights include:
Courtship
- Elaborate aerial displays, swoops, and calls
- Fish gifts presented from male to female
- Forming pair bonds for life
- Scrape nests dug in gravelly tundra
Parenting
- 1-3 speckled olive/brown eggs laid
- Both parents incubate eggs for 21-25 days
- Young fed fish and invertebrates by parents
- Chicks fledge at age 20-25 days
- Parents continue feeding fledglings at sea
Defense
- Mob intruders with loud alarm calls
- Dive-bomb humans and predators
- Fight with beaks and claws to protect young
- Distract predators by faking wing injuries
The arctic terns aggressively defend their nests and chicks. Their aerial agility and bravery make them a formidable opponent against much larger predators. This fierce protectiveness of offspring contributes to breeding success in their harsh northern habitat.
Diet and Foraging
The arctic tern is specially adapted for hunting fish and other prey both in the air and on the water’s surface. Their diet shifts between the Arctic and Antarctic:
Arctic Diet
- Small fish like cod, capelin, sand lance, Arctic char
- Aquatic invertebrates including shrimp, amphipods, mollusks
- Some insects and spiders
Hunting Strategies in Arctic
- Plunge diving to depths of 1-2 meters
- Surface plunging/dipping
- Hawking insects in flight
- Aerial pursuit of fish near surface
- Stealing fish from other seabirds
Antarctic Diet
- Fish like lanternfish, cod icefish, Antarctic silverfish
- Krill, squid, amphipods, copepods
- Some seal or penguin carrion
Hunting in Antarctic
- Surface plunging and dipping
- Underwater pursuit of krill swarms
- Scavenging wounded prey and leftovers
The terns exhibit flexibility in hunting strategies, allowing them to exploit the seasonal abundance of fish, krill, and other prey. Their aerobatic flight and keen vision help target prey from the air, while plunge diving and swimming give access to food below the water’s surface. This dietary adaptability is essential for the terns to acquire sufficient energy reserves for their marathon migrations between the polar regions.
Threats and Conservation
Although still abundant, arctic terns face growing threats in both their Arctic and Antarctic environments:
Threats in Arctic Breeding Areas
- Habitat loss from coastal development
- Disturbance of nesting colonies
- Increasing predation pressure from foxes, gulls, etc.
- Pollution exposure from oils spills, industrial activity
- Overfishing of food sources by humans
Threats in Antarctic Wintering Areas
- Fisheries bycatch and entanglement
- Oil spills from vessels and exploitation
- Climate change impacts on food chains
- Invasive species introductions
- Disturbance at resting and roosting sites
Conservation Actions
- Protect breeding colonies and migration stopovers
- Regulate fishing, drilling, and coastal development
- Restore degraded habitats
- Control invasive predators
- Reduce pollution from ships and industry
- Support international conservation agreements
Targeted conservation efforts across the arctic terns’ range are needed to maintain healthy populations. Since they migrate across dozens of nations, protecting the terns requires coordinated global commitment. But the extraordinary migrations of these tenacious birds should inspire our efforts to keep their epic polar journeys possible.
Conclusion
The arctic tern is a fascinating bird uniquely adapted to the extremes of Earth’s polar environments. Their breeding success relies on access to the seasonal bounty of Arctic and Antarctic food resources. Although they travel farther than any other animal in their annual migration, arctic terns demonstrate amazing resilience in the face of climatic and ecological challenges across the globe. With increasing threats from climate change, pollution, habitat loss, and disturbance, coordinated conservation efforts are essential to ensure the future of these remarkable global nomads. By protecting arctic terns and other long-distance migrants, we can help maintain nature’s connectivity across the planet’s wildest and most fragile places.