Data Zone
Justification of Red List category
This formerly widespread and abundant species now has a small, single population that is in continuing decline. For these reasons it is listed as Endangered.
Population justification
The global population of this species has declined drastically in recent decades such that previous estimates are thought to have considerably overestimated the population. The vast majority (>90%) of the population is now confined to India where, collating more than 1,400 records (eBird 2021) of the species between 2016 and 2020, and attributing maximum likely counts to critical sites, the population in India is estimated to number no more than 1,000 mature individuals with critical strongholds (containing more than 30 birds) being: the National Chambal Sanctuary, Madhya Pradesh, Uttar Pradesh and Rajasthan Morena (150 individuals); Yamuna Khadar, Delhi (44 individuals); River Godavari, Andhra Pradesh (approximately 25 individuals), Walayar Lake, Coimbatore, Tamil Nadu (35 individuals); Talab Shahi, Dhaulpur (30 individuals); Haiderpur and Narora on River Ganga (likely to be more than 30) and River Mahanadi, Odisha (likely more than 40) [P. Shaikh in litt. 2021]. The true population estimate may be substantially fewer than 1,000 mature individuals and determining an accurate estimate is a priority for future research. Populations in Nepal and Pakistan are very small and unlikely to host more than 20 and 50 birds each respectively (Inskipp et al. 2016, P. Shaikh in litt. 2021, eBird 2021). In Bangladesh, the population is also now estimated to be tiny. Despite being formerly common, extensive surveys in December 2011 and April 2012 of suitable habitat along the Jamuna and Padma rivers (199 km and 103 km were surveyed of the Jamuna and Padma respectively) failed to detect the species at all (Chowdhury et al. 2014). Six birds in breeding plumage were later sighted on a previously un-surveyed section of the Padma River in 2016, and two nests were found later that year (Kabir et al. 2016). Even accounting for the now-limited areas that have not been surveyed, the population is estimated to number no more than 30 individuals (S. Chowdhury in litt. 2021).
The population and range of this species has undergone a drastic decline in South-East Asia. The species is now regarded as extinct in Cambodia (Thomas and Poole 2003, Goes et al. 2010, Goes 2014), China (P. Holt in litt. 2021), Laos (Duckworth et al. 1999), Thailand (Treesucon and Limparungpatthanakij 2018) and Vietnam (Le et al. 2011, Craik and Le 2018). If any population does in fact persist in any of these countries, it must be extremely small. In Myanmar, extensive annual surveys along a 500-km stretch of the middle reaches of the Ayeyarwady river in 2017-2019 recorded just 3-5 birds (Zockler et al. 2020), representing a likely steep decline since 2001-2003, when 13 birds were found along a single stretch of river (Davies et al. 2004). This most-recent survey encompassed the vast majority of the species's former range in the country, such that it is estimated to contemporarily number no more than 30 birds. Overall, and acknowledging some uncertainty, the global population is estimated to number 800-1,600 mature individuals, with a best estimate in the range of 900-1,100. This species is capable of long-distance dispersal (see, e.g., Jansen 2005) such that the populations in Pakistan, India, Nepal and Bangladesh are likely to comprise a single subpopulation with some gene flow between them. This may be true also of the Myanmar population (comprising 1.3-2.5% of the global estimate), however it is rather disjunct and separated from north-east India by unsuitable habitat, so may constitute a separate subpopulation.
Trend justification
The species is inferred to be declining, although an exact rate has not been determined. This species had a range that formerly spanned from Pakistan through South Asia to Indochina, however is now principally confined to India, where >90% of the population resides. Despite being locally abundant in South-East Asia historically, it is now considered extinct there except for a few pairs in Myanmar (Zockler et al. 2020). With such a catastrophic range contraction, the species is inferred to have declined rapidly. Such declines continue: the species is no longer present at numerous sites in India it bred even a decade ago (eBird 2021, P. Shaikh in litt. 2021). Limited data from Myanmar suggest it also continues to decline: extensive surveys along a 500-km stretch of the middle reaches of the Ayeyarwady river (including all formerly surveyed areas for this species) in 2017-2019 recorded just 3-5 birds (Zockler et al. 2020), representing a likely steep decline since 2001-2003, when 13 birds were found along a single stretch of river (Davies et al. 2004). In Bangladesh, a count of 98 birds was made at Sirajganj in 1995; the species is now apparently extinct in this area (Chowdhury et al. 2014). The threats affecting this species are not abating and may be getting worse, with worryingly low breeding productivity now recorded at the species' stronghold, Chambal, in India (P. Shaikh in litt. 2021).
Sterna acuticauda now has the majority of its range in India where it remains widespread but in decline. It occurs also (with likely no more than 30 individuals in each) in Pakistan, Nepal and Bangladesh, and was recently confirmed to persist in Myanmar (Zockler et al. 2020) despite previous suggestion it had gone extinct there - the remnant population however is very small. The species is now thought to be extirpated in South-East Asia away from Myanmar: with no records for over a decade from Thailand, Laos, Cambodia or Viet Nam (Duckworth et al. 1999, Goes 2014, Treesucon and Limparungpatthanakij 2018, Craik and Le 2018). The small population in Yunnan, China is thought to be now extinct also (P. Holt in litt. 2021). Despite its large range the population is now estimated to number only 800-1,600 mature individuals, representing a substantial depletion given it was previously described as an abundant species throughout most of its erstwhile range.
It is found on large rivers (usually breeding on sandspits and islands) and marshes, occasionally on smaller pools and ditches, in lowlands (but not on the coast), up to 730 m.
Threats include the destruction of breeding habitat (islands and sandspits in larger rivers are increasingly cultivated), the collection of eggs for food, illegal fishing in protected areas (e.g. in Nepal [Inskipp et al. 2016]), overfishing and the flooding of nests, often caused by dams. Increased disturbance and over-harvesting of wetland products are blamed for the recent complete disappearance of the breeding population within Chitwan National Park (Nepal) (F. Cuthbert in litt. 2002). Inadequate fish ladders at Koshi Barrage may also be impacting on this species (Inskipp et al. 2016). River damming, disturbance, predation by dogs and egg collecting are highlighted as causes of the species’s disappearance from Cambodia (Goes et al. 2010). In India, the species is facing major threats due to low water levels and reduced flow rates, connecting the nesting sandbars to the bank and resulting in predation by free-ranging dogs and trampling by cattle. Many of the major river systems are under tremendous pressure of water demand: some rivers, e.g., the Chambal, are badly affected by damming upstream and the existence of several lift irrigation plants has resulted in dropping water levels (P. Shaikh in litt. 2021). Sand mining is an emerging threat for breeding colonies and it may have a long-term effect on the formation and maintenance of sandbars. Frequent stochastic weather events like sand storms, heavy pre-monsoon showers and tropical cyclone can also destroy nests. The breeding habitat on the River Ganga is under anthropogenic pressure, such as the congregation of people due to religious gatherings, agriculture practises on river islands, overfishing and pollution from the major cities of north India (A. Kumar. in litt. 2019). On the River Mahanadi in Odisha, an increase in the water level caused flooding and submergence of nests (Kar et al. 2019). In Bangladesh, Large-billed Crows (Corvus macrorhynchos) and feral dogs were the only predators observed around the nesting areas of Black-belled Tern in May 2016. Local fishermen reported that children collect eggs and chicks from sandbanks, which may pose a substantial threat to ground-nesting birds. Other forms of human disturbance include grazing and movement of large numbers of cattle, frequent visits by inexperienced bird photographers, sand extraction and harvesting of grass from the sandbars (Kabir et al. 2016).
Conservation Actions Underway
It is known from a number of protected areas throughout its range, including National Chambal Sanctuary, Bhitarkanika National Park, Satkosia Tiger Reserve, Harike Wildlife Sanctuary, Keoladeo National Park, Rajiv Gandhi National Park, Dibru-Saikhowa National Park, Kaziranga National Park, Koshi Tappu Wildlife Reserve and Chitwan National Park. Conservation Actions Proposed
Conduct coordinated surveys in India, Bangladesh, Nepal and Pakistan during the breeding period (April-May) to refine the global population estimate. Establish riverine protected areas in Bangladesh where breeding populations still exist. Conduct detailed research for understanding the nesting success and design a monitoring programme for the species. Maintaining sufficient water levels around breeding sites or restoring the flow regimes to prevent loss of nesting islands during the breeding season. Rivers in India are under tremendous pressure of water demand; hence all future water-supply projects are subjected to cumulative impact assessments, including their impact on riverine ground nesting waterbirds. Involvement of local communities in nest-site protection can be a conservation solution for protecting a few important sites. Continue to monitor population trends carefully throughout the species' range.
33 cm. Small tern. Breeding adults have orange bill, black cap and nape, dark grey breast and blackish belly and vent. Non-breeding birds show a whitish belly and lack tail streamers and the orange bill has a dark tip. Similar spp Told from other terns by smaller size and orange bill. Voice A clear piping "peuo".
Text account compilers
Berryman, A.
Contributors
Baral, H.S., Benstead, P., Butchart, S., Choudhury, S., Chowdhury, S.U., Cuthbert, F.J., Davidson, P., Duckworth, W., Eames, J.C., Holt, P., Htin Hla, T., Inskipp, C., Khan, A.A., Kumar, A., Li, Z.W.D., Mahood, S., Martin, R., Palei, H., Parveen, A., Poole, C., Praveen, J., Rafeek, K., Rahmani, A., Shaikh, P. A., Singh, A.P., Sundar, G., Taylor, J., Thompson, P., Timmins, R.J., Westrip, J.R.S. & Yasmeen, R.
Recommended citation
BirdLife International (2024) Species factsheet: Black-bellied Tern Sterna acuticauda. Downloaded from
https://datazone.birdlife.org/species/factsheet/black-bellied-tern-sterna-acuticauda on 23/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 23/12/2024.