River Tern

The river tern (Sterna aurantia) is a medium-sized tern native to South and Southeast Asia. It is identifiable by its bright yellow beak, a black cap that extends from the forehead to the nape during the breeding season, and a white body with grey wings. Adult river terns measure about 38–46 cm (15-18 in) in length with a wingspan of 80–85 cm (31-33 in), making them similar in size to other terns but distinguishable by their distinctive yellow beak and black head. Within its range it could be confused with the rare and endangered black-bellied tern (Sterna acuticauda), which is smaller, have a distinct black belly and an overall darker plumage.

River terns are typically found in freshwater habitats such as rivers, lakes, and reservoirs, where they rely on abundant fish populations for sustenance. Their diet primarily consists of small fish, though they also consume insects, crustaceans, and occasionally amphibians. River terns are skillful hunters, performing plunge-dives into the water to catch their prey. They often hover above the water’s surface, keenly watching for fish before executing a quick, precise dive.

These birds are highly adaptable and can thrive in a range of aquatic environments, provided there is a sufficient food supply. Their habitat preference for large, open bodies of freshwater makes them particularly sensitive to changes in water quality and availability. Unlike many other terns, this species is rarely seen along coasts.

River terns are generally gregarious birds, often seen in small flocks, especially outside the breeding season. They are known for their graceful flight, characterized by slow, deliberate wingbeats. While they are social in nature, forming loose colonies during the breeding season, they are also territorial and will aggressively defend their nesting sites from intruders.

River terns communicate through a variety of calls, most notably a sharp, piercing “kirrr,” which is often heard during flight. These calls play a significant role in maintaining contact between individuals, especially in the dense environments where they breed.

The breeding season of the river tern typically begins in late winter and extends through the early summer months, with timing varying slightly depending on the region. River terns are ground-nesters, preferring to lay their eggs on sandbanks, river islands, or other open areas near water. These sites are often chosen for their isolation, which provides some protection from predators.

Females usually lay two to three eggs per clutch, which are pale in color and well-camouflaged against the sandy or gravelly substrate. Both parents share incubation duties, which last for about 21–25 days. After hatching, the chicks are semi-precocial, meaning they are relatively well-developed but still rely on their parents for feeding and protection. The fledging period typically lasts around 28–35 days, after which the young birds are capable of sustained flight and begin to develop independence.

The river tern is currently classified as vulnerable by the IUCN Red List. The species faces several threats, primarily due to habitat loss and degradation. The construction of dams and water management practices have led to significant changes in river systems, reducing the availability of suitable breeding sites. Additionally, pollution and overfishing in some areas have further impacted their food supply. Despite these challenges, river tern populations are still relatively widespread, though they are in decline in some regions. Conservation efforts are focused on protecting key habitats, especially during the breeding season, and mitigating the impacts of human activities on river systems.