Brown‐headed Gull (Chroicocephalus brunnicephalus) – A Detailed Study

The Brown-headed Gull (Chroicocephalus brunnicephalus) is a medium-sized migratory gull found in various parts of Asia, including India. It is known for its distinctive brown head during the breeding season and its preference for inland water bodies and coastal regions. Below is a comprehensive overview of this species, including its taxonomy, morphology, habitat, behavior, conservation status, and its presence in the Sundarban ecosystem.

1. Taxonomy & Classification

• Kingdom: Animalia
• Phylum: Chordata
• Class: Aves
• Order: Charadriiformes
• Family: Laridae
• Genus: Chroicocephalus
• Species: Chroicocephalus brunnicephalus
• Common Name: Brown-headed Gull

The species was first described by Jerdon in 1840, and it was earlier placed under the genus Larus before being reclassified into Chroicocephalus based on genetic and morphological studies.

2. Morphology & Identification

General Appearance

The Brown-headed Gull is a medium-sized gull with distinctive seasonal plumage. It is often confused with the Black-headed Gull (Chroicocephalus ridibundus), but has unique features that differentiate it.

Physical Features

• Size: 40–42 cm in length
• Wingspan: 110–135 cm
• Weight: 400–600 g
• Coloration:
  • Breeding Season: The head turns a dark brown color, giving the species its name. The body remains white, while the wings are grey with black tips.
  • Non-Breeding Season: The head becomes mostly white, with only a faint brownish mark behind the eye.
• Beak: Medium-sized, bright red with a slightly darker tip.
• Legs: Reddish to dark orange, webbed for efficient swimming.
• Eyes: Dark with a thin white eyering.

Flight Pattern

The Brown-headed Gull has a graceful flight with deep, steady wingbeats. It soars elegantly and is often seen gliding over water bodies, using air currents for effortless travel.

3. Habitat & Distribution

The species primarily inhabits lakes, rivers, estuaries, and coastal regions but also ventures into inland water bodies.

Geographical Range

• Breeding Range: Primarily found in the high-altitude lakes of Central Asia, including Tibet, Mongolia, and western China.
• Wintering Range: Migrates southward to India, Bangladesh, Myanmar, Thailand, and coastal regions of Southeast Asia.

Habitat Preferences

• Breeding Grounds: Nesting occurs around freshwater and saline lakes at high elevations (3,500–5,000 meters).
• Wintering Sites: Prefers estuaries, coastal mudflats, large lakes, and riverine ecosystems.
• Behavior: Often seen in flocks, sometimes mingling with other gull species in search of food.

4. Diet & Foraging Behavior

The Brown-headed Gull is an opportunistic feeder, adapting its diet based on availability.

Primary Diet Components

• Aquatic invertebrates (crustaceans, mollusks, insects)
• Small fish
• Carrion and human food scraps (often scavenges near fishing ports)
• Plant matter (occasionally consumes grains and seeds)

Feeding Strategy

• Surface feeding: Often seen picking food from the water surface.
• Dipping & plunging: Occasionally dives shallowly for small fish.
• Scavenging: Takes advantage of fishing activity and human waste.

5. Breeding & Reproduction

The Brown-headed Gull breeds in colonies, often with other gull species.

Key Breeding Characteristics

• Breeding Season: April to July (mostly in Central Asian highlands).
• Nesting Sites: Prefers small islands, lakeshores, and marshes.
• Nest: Made of grass, reeds, and feathers, often built on the ground.
• Clutch Size: 2–4 eggs per breeding season.
• Incubation: Around 22–25 days, with both parents participating.
• Chick Development: Chicks are semi-precocial, meaning they can move soon after hatching but depend on parents for food.

6. Conservation Status

• IUCN Status: Least Concern (LC)
• Threats:
  • Habitat destruction (wetland loss due to human encroachment)
  • Pollution (plastic and chemical contamination in water bodies)
  • Disturbance in breeding grounds due to tourism and infrastructure projects
  • Overfishing, which affects food availability

Though not currently under major threat, continued monitoring is essential to protect this species’ breeding and wintering habitats.

7. Presence in the Sundarban Ecosystem

The Sundarban, the world’s largest mangrove forest, is a crucial wintering ground for several migratory birds, including the Brown-headed Gull.

Observation in Sundarban

• The species is not a permanent resident of Sundarban but appears during winter (November–March) as part of its migratory pattern.
• Often spotted near estuaries, tidal rivers, and coastal mudflats, where it forages for small fish and crustaceans.
• Found in mixed flocks with other gulls and terns.

Importance of Sundarban for This Species

• Rich Biodiversity: Sundarban’s vast network of estuarine waters provides ample food resources.
• Undisturbed Roosting Sites: Many islands and sandbanks offer safe resting grounds.
• Prey Availability: The abundance of fish and invertebrates supports migratory gull populations.

Potential Threats in Sundarban

• Climate Change: Rising sea levels and increased salinity may affect prey availability.
• Pollution: Oil spills and plastic waste threaten water quality.
• Human Disturbance: Unregulated tourism can disrupt feeding and roosting sites.

8. Conclusion

The Brown-headed Gull (Chroicocephalus brunnicephalus) is an elegant and adaptable species that plays a vital role in maintaining aquatic ecosystem balance. Though it primarily breeds in high-altitude lakes, its migration to Sundarban and other coastal regions highlights its ecological versatility.

Sundarban serves as a critical wintering habitat, offering ample food and resting areas. However, conservation efforts must be taken to ensure that climate change, pollution, and human disturbances do not affect its migratory patterns and survival.

This species is an indicator of wetland health, and preserving its habitats will not only protect the Brown-headed Gull but also ensure the ecological stability of Sundarban and other wetland ecosystems across Asia.