Bridled Tern (Nhàn lưng đen, Yến hông nâu)
Conservation status: LC
The Bridled Tern (scientific name: Onychoprion anaethetus, often referred to as Nhàn lưng nâu in Vietnamese) is a widespread seabird found in tropical and subtropical oceans around the world.
Here's some information about this fascinating bird:
1. Characteristics:
Appearance: It's a medium-sized tern, similar in size to the Sandwich Tern, measuring 33–36 cm (13–14 in) in length with a wingspan of 82–94 cm (34–37 in). Its wings are long and pointed, with dark brownish-grey upperparts and white underparts.
It has a distinctive blackish crown, nape, and mask, contrasting with a whitish forehead patch and a thin whitish nuchal band. The bill, legs, and feet are black. Breeding adults have a cleaner white forehead and a short eyebrow. Behavior: Bridled Terns are largely aerial and marine, seldom diving. They prefer to pick food from the water's surface, often hovering or gliding close to the sea.
They are social birds and congregate in large numbers, especially during breeding.
2. Habitat and Distribution:
Breeding Habitat: They breed colonially on offshore rocky islands (limestone and volcanic), vegetated coral cays, and exposed reefs.
They can also be found nesting on sandy dunes, under low vegetation, and in cliff-holes in some colonies. Non-breeding Habitat: Entirely aerial and marine during the non-breeding season, ranging over waters with higher sea-surface salinities.
Distribution: Their widespread breeding range includes the subtropical and tropical West Pacific, Atlantic, and Indian Oceans. In the East Asian-Australasian Flyway, they breed on the west coast of Thailand, the east Gulf of Thailand, Malaysia, Indonesia, Australia, the Philippines, and islands off Southeast China.
3. Diet:
Bridled Terns are piscivores, primarily eating fish.
4. Breeding:
Colonial Breeders: Bridled Terns breed in colonies on rocky islands.
Nesting: They typically create a ground scrape or nest in a hole.
Eggs: They usually lay one egg per clutch.
Breeding Cycle: Some populations exhibit synchronous, subannual breeding cycles (breeding interval less than one year) that coincide with their molt.
The incubation period is around 28-30 days. Partners: Some breeding pairs maintain the same partners over successive seasons.
Mixed Colonies: They are frequently found in mixed colonies with other tern species like Black-naped Terns and Roseate Terns in South China and Southeast Asian waters.
5. Migration:
Bridled Terns are migratory seabirds.
6. Conservation Status:
The Bridled Tern is classified as Least Concern by the IUCN Red List of Threatened Species (BirdLife International 2019), indicating a relatively stable and widespread population globally.
