Archived 2011-2012 topics: River Tern (Sterna aurantia): request for information

Initial deadline for comments: 31 January 2012 [note that this has been moved back by about two months].

BirdLife species factsheet for River Tern

River Tern Sterna aurantia inhabits rivers and freshwater lakes in the Indian Subcontinent, South-East Asia and southern China, also occurring rarely on estuaries, and breeds on sandy islands (del Hoyo et al. 1996). This species is listed as being of Least Concern on the basis that it is not thought to approach the thresholds for Vulnerable under any of the IUCN criteria.

This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence of less than 20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (at least a 30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (fewer than 10,000 mature individuals with a continuing decline estimated to be at least 10% over ten years or three generations, or with a specified population structure).

Despite its current Red List category, the present status of this widespread species is poorly understood. Nesting areas are vulnerable to flooding, predation and disturbance (del Hoyo et al. 1996). It has reportedly declined in abundance in Thailand, where it is now considered very rare (del Hoyo et al.1996). The species has also declined in Laos since the early 20th century, probably owing mainly to excessive human disturbance on sandbars (Thewlis et al. 1998). The multitude of hydroelectric dam projects completed, underway or planned in South-East Asia (e.g. Thewlis et al. 1998) may also threaten the species through changes to flow regime and flooding of nest-sites. In contrast, the species is now more regular in southern India than was once thought.

Further information on this species is requested, with particular emphasis on population trends and details of potential threats. If the available evidence suggests that the overall rate of decline has approached 30% (typically 20-29%) over the past three generations, estimated by BirdLife to be c.30 years in this species, then it may be eligible for uplisting to Near Threatened under the A criterion. If evidence supports the suspicion of a decline of at least 30% over the past 30 years the species could qualify for uplisting to Vulnerable.


del Hoyo, J., Elliott, A. and Sargatal, J. (1996) Handbook of the birds of the world, Vol 3: Hoatzin to Auks. Barcelona, Spain: Lynx Edicions.

Thewlis, R. M., Timmins, R. J., Evans, T. D. and Duckworth, J. W. (1998) The conservation status of birds in Laos: a review of key species. Bird Conserv. Int. 8 (Suppl.): 1-159.

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10 Responses to Archived 2011-2012 topics: River Tern (Sterna aurantia): request for information

  1. Joe Taylor says:

    The following wording, regarding the species’s status in Cambodia, has been extracted from a document sent by Frédéric Goes on 14 October 2011:

    At Risk in Laos / Critical in Thailand / Threatened in Cambodia. Northeast Cambodia supports the entire remaining Mekong population of the species. This population probably numbers in the low to mid-hundreds pairs, with its stronghold in the two braided sections of the upper Cambodian Mekong. It is certainly declining throughout, although probably at different pace. Dramatic declines have taken place on the two main tributary populations in recent years . . . The Srepok population is marginal and the Mekong population is now the last stronghold of the species in the region, and is of very high regional significance. No indication of sharp decline has been detected so far in this part of the population. Clearly, in view of its near certain decline (for the same reasons as other riverine-nesting species), its vulnerability and the landscape wide threat of planned Mekong mainstream dams, the species qualifies as nationally Threatened.

  2. Joe Taylor says:

    The following comment was received from Andrea Claassen on 7 November 2011, regarding the species’s status in Cambodia and in reaction to the document sent by Frédéric Goes:

    Actually, numbers do seem to have declined sharply between 2007 and 2011. The largest breeding colony on the Mekong contained 30-40 pairs in 2007 (Timmins 2008) and only 5-6 pairs in 20010-11 (Claassen unpublished data). There were also fewer locations that contained pairs in 2010-11 than in 2007 (Claassen [unpublished data]).

  3. Joe Taylor says:

    The following comments were sent by Richard Thewlis on 15 November 2011:

    Interesting that this species is not considered even vulnerable [presumably] due to it’s huge range, throughout most of which sizeable populations still exist. It was interesting to read Frederic Goes comments of the importance of the Cambodian Mekong population, and also of the decline reported on the Lao Mekong by Andrea Claassen since the 1990s. When I was in Laos in the 1990s we expected more River Terns than we saw, and the species had massively declined since the days of the early explorers like Delacour and Jabouille. I think this is pointed out in Thewlis et al. (1998). I can’t comment on birds in South China as I’ve not been there – perhaps good numbers still exist there?
    Likewise I don’t know about the Indian subcontinent, but presumably good numbers still occur there, hence the decision to maintain the species as Least Concern? However, I would not be surprised if it is in decline there too – it’s hard to get quantifiable data.

  4. Carol Inskipp and Hem Sagar Baral says:

    River Tern is now a rare and very local visitor in Nepal. It was assessed as Critically Endangered under the criteria A2a, C2a(i) and D1 in The State of Nepal’s Birds 2010 published by Bird Conservation Nepal and the Department of National Parks and Wildlife Conservation, Kathmandu. The species was very recently re-assessed under the same categories and using the same criteria for the Nepal Red Data Book which is currently being researched and written (to be published by the Zoological Society of London). The assessments were based on the sharp decline in its population since at least the early 1990s and its very small population size. The distributional range of the species has also reduced since at least the early 1990s. In the late 1940s and up to at least the 1970s it was common on rivers, streams and marshy lakes of the terai but now River Tern is now mainly recorded from only two localities (Koshi Barrage/Koshi Tappu Wildlife Reserve and Bardia National Park). The exceptional number of 450 was estimated in November 1984 at Koshi. Around 100 were seen there in March 1982 and in February and March 1987, 50 in April 1985, and 60 in March 1989. Numbers recorded at Koshi Barrage and in Koshi Tappu Wildlife Reserve have gradually dwindled and only single birds have been noted irregularly after 2004. Small numbers have been recorded from the Karnali River in Bardia National Park since the early 1990s e.g. eight in March 1992, ten in February 1995, six in February 2000, five in March 2005, four in May 2008, and one in January 2010. In Chitwan National Park in the early 1980s the species was considered to be a fairly common resident that possibly bred, but there are only two recent records (one bird in 1992 and three in 2007). River Tern is severely threatened by food shortage and disturbance and destruction of its breeding habitats on rivers. A maximum current population of 20 has been estimated for the Nepal bird Red Data Book (in prep.).

    The above information is a summary of the species account written for the Nepal bird Red Data Book- a full account including references has been sent to Stuart Butchart and Mike Crosby at BirdLife.

  5. Joe Taylor says:

    The following comments were sent by Will Duckworth on 24 November 2011:

    From a Lao perspective the species is so close to extirpated and that this had occurred by 1992 and thus the ‘last 3 generations’ window does not capture what must have been a spectacular decline to witness, that its global Red List status depends on elsewhere. However, it is difficult to believe that the factors that did for it in Lao are not operating to some extent throughout its range.

  6. Yang Liu says:

    In China, recent records were from Dayingjiang River, SW Yunnan all year round. My impression is that it is uncommon in this region because normally less than ten individuals can be sighted in a same day. The habitat may be under threat due to construction of dams in Dayingjiang region.

  7. Joe Taylor says:

    The following comment, regarding the species’s status in Cambodia, was submitted on behalf of Andrea Claassen on 22 December 2011:

    In view of its historical and recent precipitous decline, the species is heading towards extinction in 5-10 years if no specific conservation action is undertaken.

  8. Praveen J says:

    Status in Kerala, SW India: Though unrecorded by Dr. Salim Ali during the Travancore-Cochin survey (1933) nor until the publication of Birds of Kerala (1969), River Tern has been benifited by the dams and manmade reservoirs on the west flowing rivers of the Western Ghats. Breeding atleast in the islets of five reservoirs in the state, the bird is now widespread in winter in almost all the inland reservoirs of Kerala. Largest AWC count (between 1987 & 2007) from the state was 106 birds in 1999 – perhaps the year when the coverage of inland reservoirs.
    Source: Birds of Kerala – Status & Distribution: C Sashikumar, Praveen J, Muhamad Jafer Palot & P O Nameer

    Status in South India: Though there are no estimates or counts available I can cite of – the bird has been doing well in South India based on sight & photographic reports in recent years, breeding in certain locations (Ranganathittu, Bhadra WLs etc) and I believe is not threatened to the scale of Black-bellied Tern.

  9. It is one of the most common bird seen in every tank, lake and at Pennar River in Andhra Pradesh, India. The population of Indian River Tern is stable hear, no declined but incresed in Last 10 years and the bird is doing well in Andhra Pradesh.
    S. Riyaz uddin,

  10. I have seen this magnificent tern on 11-1-12 near my home in Munderi wetland in Kannur District,Northern parts of Kerala, south India.There were 2 terns foraging over marsh land. This is the first time I have seen this bird there.The River is very salty now.

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