White‐winged Tern (Chlidonias leucopterus) – A Detailed Analysis

The White‐winged Tern (Chlidonias leucopterus), a small and elegant marsh tern, is a fascinating species known for its striking seasonal plumage and wide distribution. This species belongs to the family Laridae, which includes gulls and terns, and is recognized for its distinct migratory behavior.

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Taxonomy & Classification

• Kingdom: Animalia
• Phylum: Chordata
• Class: Aves
• Order: Charadriiformes
• Family: Laridae
• Genus: Chlidonias
• Species: Chlidonias leucopterus

The White‐winged Tern is closely related to other marsh terns, such as the Black Tern (Chlidonias niger) and Whiskered Tern (Chlidonias hybrida), all of which share similar habitat preferences.

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Morphological Characteristics

Size & Structure

• Small-sized tern, measuring 22–27 cm in length.
• Wingspan ranges from 57–67 cm.
• Weight varies between 55–80 grams.

Plumage & Seasonal Variation

• Breeding Plumage:

  • Striking black head, breast, and belly.
  • Contrasting white wings and tail, giving it its name.
  • Dark grayish back with pale underwing coverts.

• Non-breeding Plumage:

  • Transforms into a more subdued appearance with a white body and pale gray upperparts.
  • Retains a small dark patch on the ear-coverts.
  • Bill turns from black (breeding) to reddish-black (non-breeding).

Beak & Legs

• The beak is short, slender, and pointed, adapted for catching insects and small fish.
• Legs are relatively short and reddish-black in color.

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Habitat & Distribution

Global Range

The White‐winged Tern is widely distributed across Europe, Asia, and Africa, with different populations migrating seasonally.

• Breeding Range: Found in Eastern Europe and Central Asia, particularly in marshes, freshwater wetlands, and lakes.
• Wintering Grounds: Migrates to Africa, the Indian subcontinent, and Southeast Asia, preferring coastal areas, estuaries, and inland wetlands.

Presence in the Sundarban Ecosystem

The Sundarban mangrove ecosystem, situated in India and Bangladesh, is an important wintering ground for this species.

• Migratory Status in Sundarban:

  • The White‐winged Tern is a regular winter visitor to the Sundarban delta, arriving between October and March.
  • It is often seen foraging over the shallow waters, tidal creeks, and mudflats of the region.
  • Forms mixed flocks with other terns and waders, particularly in the estuaries and saline wetlands.

• Preferred Habitats in Sundarban:

  • Mangrove-lined tidal rivers & estuaries
  • Brackish water lagoons & mudflats
  • Open marshlands near river mouths

• Role in the Sundarban Ecosystem:

  • Acts as a bio-indicator of wetland health, as it relies on clean water and a healthy prey population.
  • Helps control insect populations by feeding on aquatic invertebrates and small fish.

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Feeding Behavior & Diet

• Diet Composition:

  • Primarily insectivorous, feeding on dragonflies, mayflies, beetles, and flies.
  • Occasionally consumes small fish, crustaceans, and amphibians.

• Hunting Strategy:

  • Aerial foraging: Captures insects in flight with swift, agile movements.
  • Surface picking: Skims over the water, plucking prey from the surface.
  • Shallow diving: Occasionally dives into the water to catch fish.

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Breeding & Nesting Behavior

• Breeding Season: April to July

• Nesting Sites:

  • Prefers shallow freshwater marshes with floating vegetation.
  • Nests in small colonies, often alongside other marsh terns.

• Nest Construction:

  • Made of aquatic vegetation, forming a floating platform.
  • Positioned close to reeds and grasses for protection.

• Eggs & Incubation:

  • Lays 2-3 eggs, which are olive-brown with dark speckles.
  • Both male and female participate in incubation (18-21 days).

• Chick Development:

  • Precocial chicks, covered in down, leave the nest within a few days.
  • Fully fledged in 3-4 weeks.

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Special Features & Adaptations

1. Highly Migratory Nature

   • Travels thousands of kilometers annually, adapting to different climatic zones.

2. Seasonal Plumage Change

   • The stark contrast between breeding and non-breeding plumage helps with camouflage and mating displays.

3. Aerial Foraging Skills

   • Agile and swift, capable of catching prey mid-flight or skimming the water surface.

4. Colony Nesting

   • Forms dense breeding colonies, which provide safety from predators.

5. Flexibility in Habitat Use

   • Can thrive in both freshwater and brackish wetlands, making it resilient to environmental changes.

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Conservation Status & Threats

• IUCN Red List Status: Least Concern (LC)
• Population Trend: Stable, but localized declines due to habitat destruction.

Major Threats

1. Wetland Degradation:

   • Draining of marshes and wetlands for agriculture and urban expansion.

2. Climate Change:

   • Rising sea levels and extreme weather impact nesting and wintering grounds.

3. Pollution:

   • Water contamination from pesticides, plastic waste, and industrial effluents.

4. Human Disturbance:

   • Increased tourism and fishing activities disrupt foraging and resting sites.

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Conclusion

The White‐winged Tern (Chlidonias leucopterus) is a remarkable migratory bird that plays an essential role in wetland ecosystems. Its seasonal presence in the Sundarban highlights the importance of this unique mangrove habitat as a vital wintering ground. Conservation efforts focusing on wetland protection, pollution control, and climate resilience are crucial to ensuring the continued survival of this species in the Sundarban and beyond.

By protecting the Sundarban ecosystem, we not only safeguard the habitat of the White‐winged Tern but also ensure the survival of many other migratory and resident bird species that depend on this rich and biodiverse region.