Sterna aurantia

The forehead, crown, and occipital parts, including the crown feathers and the entire top of the head from the eye margin to the ear, are black and have a green metallic luster, which is distinct from the Gull and Gull species. The lower margin of the eye has a star-shaped white spot. The covers on the back, shoulders, and wings are dark gray. The color of the waist, upper tail cover, and tail feathers is pale gray, while the outer two pairs of tail feathers are almost white. The outer tail feathers are particularly prolonged and pointed, giving the tail feathers a deep forked shape, unlike the shorter tail feathers of floating gulls. Below the eyes, the head, neck, chin, throat, and the entire lower body are white. The forehead of Dongyu is dark white. The head and occipital are dark gray, with white stripes, and the eye area and ear coverts are black. The rest is very similar to Natsuyu.
Iris dark brown or blue-black. The bill is yellow, dark in winter and has black tips, the feet

Resident birds: Bangladesh, Cambodia, China, India, Myanmar, Pakistan and Thailand.
Non-breeding areas: Bhutan, Laos, Nepal and Vietnam.
Wandering (non-breeding) : Afghanistan and Iran.
In China, it is distributed in the Yingjiang River and Longchuanjiang River valleys on the western slope of the southern section of the Galigong Mountains in western Yunnan, and in the Xishuangbanna region in the south.
It is found in river areas of mountains and plains, and sometimes in large lakes and swamps along rivers. Inhabiting rivers and freshwater lakes, rarely occurring in estuaries, it breeds on sandy and rocky islands, especially along rivers. It breeds in high densities in large reservoirs and rivers as well as natural and constructed wetlands in India. Due to temporary exposure after irrigation and water management from nearby reservoirs, some sandbars may also be used for nesting. In Nepal, people have been recorded living at altitudes of up to 600 m.

River Tern is a medium-sized waterfowl with no subspecies.

River terns are resident birds. They often live alone or in small groups of 2-3. They fly frequently over rivers and rarely stop. Flying light and agile, slow and leisurely, between the green mountains and green water, after finding food, quickly fall into the water, after eating and then rise into the air.

River terns feed mainly on small fish, but also frogs, tadpoles, crustaceans, and aquatic insects. The flight is slow and powerful, and the slender wings and tail are distinctive. Mixing with other terns. Often resting on sandbanks.

River terns breed from March to May. They nest in the sand on the banks of remote rivers. The nest is usually a shallow pit dug in the sand by the parent bird. Each clutch lays 3 eggs, occasionally as few as 2 and as many as 4. The eggs are pale sandy or yellowish in color, with brown, reddish-brown, or purplish-brown spots. The eggs are incubated by male and female birds in turn. Incubation period is 18-19 days.

River terns were once widely distributed in southern Asia, being found in Pakistan, India, Nepal, Bhutan, Bangladesh, Myanmar, Thailand, Laos, Cambodia, Vietnam, and southern China (Yunnan), and travellers have been recorded in Iran and Afghanistan, although usually resident throughout most of their range. The global population is estimated at 50,000 to 100,000 individuals (Delaney and Scott 2006). But it has reportedly become very rare in Thailand. The species has also declined in Laos since the early 20th century and is very close to the brink of extinction (W. Duckworth in litt. 2011).

As of 2011, it is also known to be in decline across Cambodia, and in the largest wild breeding area of the Mekong River, breeding populations also declined significantly between 2007 and 2011. Given its history and recent sharp decline in Cambodia, the species will go extinct in the region in 5-10 years if concrete conservation measures are not taken. The species has become so rare in Nepal that it is only occasionally seen by locals and rarely seen by non-local visitors, with only 20 individuals estimated in 2011, a rapid decline from a peak in the 1990s. The species enters Southeast Asia along the Daying River in southwestern Yunnan Province, China, and occurs more frequently in southern India, possibly benefiting from the development of reservoirs (Praveen J. in litt. 2012). Similarly, the species is described in Andhra Pradesh, India, and has increased in the last 10 years (S. Riyazuddin in litt. 2012).

Previous Asian waterbird censuses observed 5,733 river terns in the period 1987-1992, 5,558 in the period 1993-1997, 9,963 in the period 1998-2002. 7,578 were observed in some Indian and Pakistani sites during 2003-2007 (Li et al. 2009). Further surveys conducted throughout Asia and Australasia between 2008-2015 found 39 individuals in Myanmar, 2 in Thailand, 74 in Bangladesh, 17,776 in India, 31 in Nepal, 11,48 in Pakistan, 5 and 170 in Cambodia (Mundkur et al., 2017). However, undercounting is considered a major factor. The Southeast Asian portion of its range is very small in number and has a higher risk of extinction (F. Goes in litt 2020). For example, in the entire Mekong River basin, there are estimated to be fewer than 100 river terns (F. Goes in litt 2020). Therefore, using the best available information, assuming that some surveys may have been underestimated, the number is thought to be at least 29,500 individuals and possibly up to 100,000 individuals. Therefore, using a rounded number scale of 30,000-100,000 individuals, the number is placed in the range of 20,000-70,000 mature individuals.

Listed on the IUCN Red List of Threatened Species (IUCN)ver 3.1:2020 - Vulnerable (VU)

Listed in China's "National Key Protected Wildlife List" (February 5, 2021).

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