Arctic terns are seabirds that breed in the Arctic and subarctic regions. They migrate long distances to spend the northern winter in warmer climates. Arctic terns build nests each spring when they return to their Arctic breeding grounds. The nests provide a place for the terns to lay and incubate their eggs and raise their chicks.
What are Arctic terns?
Arctic terns (Sterna paradisaea) are medium-sized seabirds in the family Laridae, which includes gulls, terns, and skimmers. They have a wingspan of about 75-85 cm and are around 33-37 cm long from bill to tail. Adult Arctic terns have pale grey upperparts and white underparts. Their heads are white with a black cap that extends just below the eye. Their short legs are red. Arctic terns have deeply forked tails and long, pointed wings. Their slender, pointed red bills are adapted for catching small fish and marine invertebrates.
During the northern summer, Arctic terns breed in coastal areas and inland marshes and lakes across the Arctic and subarctic regions. This includes northern parts of Europe, Asia, and North America. After breeding, Arctic terns migrate long distances to spend the northern winter in the oceans around Antarctica. Their annual migration route can cover over 90,000 km, making them the animal with the longest migration in the world.
Where do Arctic terns nest?
During the spring and summer breeding season, Arctic terns nest in colonies on coasts, islands, and inland water bodies in the Arctic and subarctic regions. Nesting habitat includes gravel or rocky areas near water, as well as marshes, bogs, wet meadows, and shoreline tundra.
Arctic terns do not build elaborate nest structures. The nest is simply a shallow scrape or depression in the ground, lined with whatever materials are available nearby. This includes things like dead marsh vegetation, straw, twigs, lichens, and moss. Arctic terns often nest in association with other tern species. Their nesting colonies can range from just a few dozen pairs to over 10,000 pairs of nesting terns.
Do Arctic terns build nests?
Yes, Arctic terns build simple nests each breeding season in which to lay and incubate their eggs and raise their chicks. The nest is an important part of their breeding biology and behavior.
While Arctic tern nests may look simple compared to the complex nests built by some bird species, they serve several important functions:
- The nest marks and defends the territory of the mated pair.
- It provides a shallow depression to safely hold the eggs.
- Insulating nest materials help regulate egg temperature during incubation.
- The nest offers some protection from predators and harsh weather.
- It provides a contained area where parents can brood young chicks.
Though rudimentary, building a nest is an essential part of preparing for breeding and reproductive success in Arctic terns. They invest energy and resources into constructing nests each season despite their nomadic lifestyle.
Arctic Tern Nesting Biology
Arctic terns exhibit a specialized nesting biology and breeding behavior that is adapted to their Extreme habitats and long migrations.
Timing of Breeding
Arctic terns arrive back at their breeding grounds in the spring as the Arctic snow and ice melts. This timing coincides with the peak availability of the small fish, marine invertebrates, and insects that terns rely on to feed themselves and their chicks.
Most Arctic terns breed for the first time when they are 2-4 years old. Upon arriving at the breeding colonies, male and female terns engage in courtship flights and calls to solidify pair bonds. Birds generally reunite with previous mates from past seasons.
Egg laying typically begins from late May to mid June depending on the latitude. The breeding season lasts around 3 months on Arctic and subarctic breeding grounds.
Egg Laying and Incubation
Once pair bonds have formed, the male and female work together to choose a nest site and build a simple scrape nest lined with available materials.
The female then lays 1-3 pale brownish or olive-colored eggs with dark splotches. The eggs are pointed at one end and oval shaped, about 45 mm long by 30 mm wide. The parents take turns incubating the eggs for around 22-25 days until they hatch.
Both sexes develop brood patches – areas of bare skin on the abdomen – to help transfer warmth to the eggs during incubation. They defend their nesting territory vigorously against potential predators or egg thieves.
Chick Rearing
Arctic tern chicks hatch over several days. The young chicks are downy with grayish-brown down, eyes closed, and rely completely on their parents for warmth, protection and food.
The chicks remain in the nest area where the parents brood them frequently to prevent exposure. Both parents collect small whole fish, marine invertebrates, and insects to feed the chicks multiple times a day.
As they grow, the semi-precocial chicks wander farther from the nests, forming small groups or creches. They fledge at around 20-25 days old, but the parents continue to feed and protect them until they are able to migrate south independently.
Nest Site Fidelity
Arctic terns exhibit nest site fidelity. They often return to nest in the same colony site year after year. Some studies have found Arctic terns exhibiting nest fidelity for over 20 years.
However, while they are loyal to nesting colony locations, they do not use the exact same nest. Nests are simple scrapes that erode away over winter. Arctic terns build new nest scrapes each spring upon arriving at the breeding colonies.
Adaptations for Nesting in the Arctic
Arctic terns are highly adapted for constructing nests and breeding in the challenging environments of the High Arctic:
Migratory Life History
The long migrations of Arctic terns are an adaptation to take advantage of abundant Arctic prey in summer and ample marine resources in Antarctica during winter. Their migratory life history allows them to breed in the productive but intensely seasonal Arctic summer.
Cold Tolerance
Arctic terns can maintain high rates of incubation and chick brooding even in freezing Arctic temperatures. Their feathers provide insulation, while underlying down feathers and brood patches aid in egg warming.
Camouflage
The countershaded plumage of Arctic terns helps camouflage them against aerial predators. Their pale gray backs and white fronts blend in against Arctic skies and terrain. Parents use distraction displays to lure potential predators away from nests.
Aggression
Arctic terns vigorously defend their nesting territories from rival terns and potential nest predators through loud calls, aerial dive bombing, and physical attacks. This aggression helps deter predation.
Colonial Nesting
Nesting in dense colonies provides safety in numbers through cooperative group defense against predators. Colonies are often situated on island or peninsula sites further isolated from mainland predators.
Cryptic Nests
Arctic tern nests are difficult to detect by predators and other terns. The shallow, scrapings blend in with the tundra landscape. Lining nests with local materials provides camouflage.
Threats to Nesting Arctic Terns
Arctic terns face threats both in their northern breeding areas and southern overwintering oceans. These can negatively impact their nesting success:
Climate Change
Rising temperatures in the Arctic are altering habitat and prey availability. Increased rainfall can flood nests, while earlier snowmelt may cause a mismatch with food sources.
Predators
Mammalian predators like foxes, bears, mink, and raccoons may rob tern colonies, as can large gulls. The decline of polar bear populations has allowed increases in smaller nest predators.
Human Disturbance
Tourism, development, fishing, recreational vehicles, and research activities in the Arctic can all unintentionally impact tern nesting habitat and success. Direct human nest disturbance prompts terns to abandon nests.
Pollution
Ocean plastic pollution and oil spills in overwintering areas can affect prey availability and poison birds. Chemical contaminants from industrial pollution can accumulate in the birds and their eggs.
| Threat | Impact on Nesting |
|---|---|
| Climate Change | Habitat loss, mismatch with prey, extreme weather |
| Predators | Decreased nest success, chick loss |
| Human Disturbance | Abandonment, reduced reproductive rates |
| Pollution | Contaminants reduce fitness, prey impacts |
Population Declines
Some Arctic tern breeding populations in North America and Europe have experienced concerning declines, likely due to a combination of threats on their breeding and overwintering grounds. Maintaining suitable Arctic habitat will be key for their future nesting success.
Conservation and Management
Several measures can help support Arctic tern nesting success in the face of anthropogenic threats:
Protected Areas
Designating Arctic National Wildlife Refuges, marine protected areas, and restricted access zones around nesting colonies can reduce disturbance.
Habitat Management
Restricting vehicles and development near nesting habitat helps minimize impacts. Habitat restoration through removing invasive plants or predators may aid colony success.
Colony Monitoring
Biologists conduct regular monitoring of Arctic tern colonies to track population trends and productivity. Banding studies assess survival and migratory routes.
Outreach
Education programs can encourage tour operators, fishermen, resource developers, and Arctic communities to take actions to conserve tern nesting habitat.
International Agreements
Agreements like the Migratory Bird Treaty Act and the Arctic Tern Working Group coordinate conservation across the species’ range between nations.
Conclusion
In summary, Arctic terns are highly specialized seabirds that build simple scrape nests each spring and summer in which to breed across the Arctic and subarctic regions. Their migratory life history and adaptations like aggression and camouflage aid in constructing and incubating nests in extremely cold and variable High Arctic environments. However, Arctic terns face escalating threats from climate change, human disturbance, pollution, and predation. Conservation measures focused on protected breeding habitats will be essential to ensure Arctic terns can continue nesting and passing on their incredible migratory traditions into the future.
