Arctic Tern (Sterna paradisaea) – The Ultimate Migratory Bird

Taxonomy

• Kingdom: Animalia
• Phylum: Chordata
• Class: Aves
• Order: Charadriiformes
• Family: Laridae
• Genus: Sterna
• Species: Sterna paradisaea

Morphology & Physical Characteristics

The Arctic Tern (Sterna paradisaea) is a medium-sized seabird known for its striking appearance and extreme migratory behavior.

• Size: 28–39 cm (11–15 inches) in length
• Wingspan: 65–75 cm (25–30 inches)
• Weight: 86–127 g (3.0–4.5 oz)
• Plumage:
  • In breeding season, it has a white body with a black cap on the head.
  • The wings are pale grey, and the underparts are mostly white.
  • The bill is deep red, along with bright red legs.
  • Non-breeding adults develop a darker tip on the bill and a whiter forehead.
• Tail: Deeply forked, giving it an elegant appearance.
• Flight Pattern: Graceful, with a buoyant and agile flight.

Habitat & Distribution

The Arctic Tern has a vast range covering both hemispheres:

• Breeding Grounds: Arctic and subarctic regions of North America, Europe, and Asia, including Greenland, Iceland, and parts of Canada.
• Wintering Grounds: Antarctic region, covering the longest migration of any bird.

This species follows a circumpolar breeding pattern, nesting in coastal tundras and islands. It prefers open ground, rocky shores, and marshy areas for nesting.

Migration: The Longest Journey in the Animal Kingdom

• The Arctic Tern is famous for having the longest migration of any bird.
• It travels approximately 70,000 km (43,500 miles) annually, from the Arctic to the Antarctic and back.
• This means it experiences two summers every year, spending almost its entire life in daylight conditions.

Diet & Feeding Behavior

• Primarily piscivorous, feeding on small fish such as herring, sand eels, and capelin.
• Also consumes crustaceans and marine invertebrates.
• Foraging Method:
  • Dives into the water from mid-air (plunge-diving).
  • Skims the water surface to catch prey.

Reproduction & Life Cycle

• Breeding Season: May to July
• Nesting:
  • Nest is a shallow scrape on the ground, often near coastal areas.
  • Both parents share incubation duties.
• Clutch Size: Usually 1–3 eggs
• Incubation Period: ~22–27 days
• Fledging Period: 21–28 days after hatching
• Lifespan: Can live up to 30 years, making multiple migrations in its lifetime.

Special Features & Adaptations

• Extreme Migration Adaptation: Capable of flying thousands of miles without stopping, using wind currents to conserve energy.
• Efficient Flight Mechanism: Long, narrow wings provide exceptional gliding ability, reducing energy consumption.
• High Survival Rate: Its migratory pattern helps it avoid many natural predators.
• Excellent Navigation Skills: Uses the Earth’s magnetic field, the Sun, and landmarks for precise orientation during migration.

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Presence of Arctic Tern (Sterna paradisaea) in Sundarban

The Sundarban, the world’s largest mangrove forest, located in the delta of the Ganges, Brahmaputra, and Meghna rivers, serves as a crucial wintering ground and migratory stopover for many seabirds.

Is Arctic Tern Found in Sundarban?

While the Arctic Tern is not a resident bird of the Sundarban, it has been observed as a passage migrant along the coasts of the Bay of Bengal during its long migratory journey.

Factors Influencing Its Presence in Sundarban

1. Geographical Location:

   • Sundarban lies on the East Asian-Australasian Flyway, a critical migratory route for many seabirds.
   • The Arctic Tern might stop briefly to feed along the coastal and estuarine regions before continuing toward the Antarctic.

2. Availability of Food:

   • The Sundarban estuaries and surrounding waters provide rich fish populations that could serve as feeding grounds.
   • However, due to the dense mangrove habitat, it is not an ideal nesting site for the Arctic Tern, which prefers open coastal areas.

3. Climate Conditions:

   • The humid tropical climate of Sundarban is vastly different from the Arctic Tern’s breeding and wintering habitats.
   • This makes it unlikely to be a long-term visitor but rather a short-term transient migrant.

4. Threats in the Region:

   • Habitat Disturbance: Increasing human activities such as fishing and tourism could disrupt any potential stopovers.
   • Climate Change: Rising sea levels and extreme weather events may alter the migratory pathways of Arctic Terns.

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Conclusion

The Arctic Tern (Sterna paradisaea) is one of nature’s most remarkable migratory birds, traveling between the Arctic and Antarctic every year. While it is not a resident species of the Sundarban, it is sometimes observed as a passage migrant along the Bay of Bengal during its long journey.

With the Sundarban’s rich biodiversity and strategic location, it plays a minor but crucial role as a potential feeding stop for these long-distance travelers. However, further studies and birdwatching records are needed to confirm its exact frequency in the region.