Gull‐billed Tern (Gelochelidon nilotica) – A Comprehensive Overview

Taxonomy & Classification

• Scientific Name: Gelochelidon nilotica
• Common Name: Gull-billed Tern
• Family: Laridae
• Order: Charadriiformes
• Genus: Gelochelidon
• IUCN Status: Least Concern (LC)

The Gull-billed Tern belongs to the family Laridae, which includes gulls and terns. It is a cosmopolitan species with a broad distribution across different continents.

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Morphology & Identification

General Appearance

The Gull-billed Tern is a medium-sized tern that exhibits unique characteristics differentiating it from other tern species.

• Size: About 33–42 cm in length
• Wingspan: Ranges from 76–91 cm
• Weight: Approximately 150–290 g

Plumage & Features

• Breeding Plumage:

  • Black cap extending from the forehead to the nape
  • Pale grayish upperparts
  • White underparts
  • Relatively short, strong, and black bill (unlike other terns, which have slender bills)
  • Legs are black

• Non-breeding Plumage:

  • The black cap fades to a more fragmented look
  • Forehead becomes white
  • Overall duller appearance

• Juvenile:

  • More mottled appearance with dusky patches on wings
  • Bill appears slightly duller

Distinctive Features

• The short, thick, and slightly down-curved bill is its most distinctive trait, setting it apart from other terns that have longer and sharper bills.
• Unlike other terns that feed primarily on fish, the Gull-billed Tern has a diverse diet, consuming insects, small vertebrates, and even chicks of other birds.

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Habitat & Distribution

The Gull-billed Tern is highly adaptable and is found in coastal and inland wetlands, including:

• Salt marshes
• Lagoons
• Estuaries
• Mudflats
• Mangroves

Global Distribution

It is found across Europe, Africa, Asia, and the Americas, mainly in temperate and tropical regions. It breeds in parts of Europe, Central Asia, and North America, migrating to Africa, South America, and South Asia during winter.

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Diet & Foraging Behavior

Unlike other terns that mainly hunt fish, the Gull-billed Tern has an opportunistic feeding strategy.

Diet Includes:

• Insects (grasshoppers, dragonflies, beetles)
• Small mammals (rodents)
• Reptiles (lizards, small snakes)
• Amphibians (frogs)
• Bird chicks & eggs
• Crustaceans

It forages over grasslands, mudflats, and wetlands, often catching prey mid-air or from the ground rather than diving into water like other terns.

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Breeding & Nesting Behavior

• Breeding Season: April to July (varies by region)
• Nesting Sites: Coastal sandbanks, marshes, islands, and riverbanks
• Nest Type: Simple scrape in sandy or muddy ground
• Clutch Size: Typically 2–3 eggs
• Incubation Period: Around 22–23 days
• Parental Care: Both parents incubate and care for chicks
• Fledging Time: Young birds take 25–30 days to fledge

The species exhibits strong site fidelity, meaning it often returns to the same nesting sites each year.

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Vocalization & Communication

The Gull-billed Tern has a harsh, nasal call, often described as a “keh-keh-keh” or “kree-kree.” It is known to be quite vocal, especially during the breeding season.

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Presence in the Sundarban Ecosystem

Gull-billed Tern in Sundarban

The Sundarban, the world’s largest mangrove ecosystem, provides an excellent habitat for the Gull-billed Tern, especially during its winter migration.

Why is Sundarban a Suitable Habitat?

• Abundant food sources: The diverse prey availability, including insects, crabs, small fish, and amphibians, makes it a prime foraging ground.
• Coastal and wetland areas: Sundarban’s mudflats, estuaries, and tidal marshes provide ideal resting and feeding zones.
• Low human disturbance in certain areas: Some regions in Sundarban National Park remain relatively undisturbed, offering safe nesting and roosting sites.

Seasonal Occurrence

The Gull-billed Tern is primarily observed in Sundarban between October and March, when it migrates from its breeding grounds in Central Asia, Europe, and North India to escape the harsh winter.

Conservation Concerns in Sundarban

Despite its Least Concern (LC) status globally, local threats include:

• Habitat destruction: Due to coastal erosion, rising sea levels, and deforestation of mangroves.
• Pollution: Industrial waste, plastic debris, and oil spills impact food sources.
• Climate change: Alters migration patterns and affects wetland ecosystems.

Importance in the Sundarban Ecosystem

• Acts as an indicator species for wetland health.
• Plays a role in controlling insect and small vertebrate populations.
• Contributes to the avian biodiversity of Sundarban, which supports a variety of migratory birds.

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Conclusion

The Gull-billed Tern (Gelochelidon nilotica) is a unique tern species known for its versatile feeding habits, broad habitat range, and distinctive morphology. In Sundarban, it thrives as a winter visitor, utilizing the rich wetland ecosystem for foraging and roosting. However, with increasing environmental threats, conservation efforts should focus on protecting wetland habitats to ensure the continued presence of this adaptable bird in the region.

Did you know?

Unlike many other terns, the Gull-billed Tern is often seen hunting far from water, sometimes even over agricultural fields and grasslands, making it one of the most adaptable members of its family!