BirdLife species factsheet for Indian Skimmer
Indian Skimmer occurs in the major river systems of Pakistan, northern India and Bangladesh. Formerly it was also common in Myanmar and along the Mekong in south-east Asia, but is now very rare in Myanmar (Chowdhury et al. 2020) and there are no recent records from Laos, Cambodia or Vietnam. The previous assessment listed the species as Vulnerable due to a suspected rapid population decline occurring in line with the widespread degradation of riverine and wetland habitat throughout the range. Concern that fewer individuals were being located in non-breeding congregations in Bangladesh (Mohsanin 2014) led to increased survey efforts. The results of these efforts to quantify the global population suggest that it is now considerably smaller than previously estimated and that the rate of population reduction is greater than thought.
Both the population during the breeding and non-breeding season have been assessed in the past two years. Breeding records are now almost all from a handful of rivers in India. A mixture of direct counts and estimates result in a total of known breeding adults (mature individuals) of 1,160 – 1,230, as follows; c. 500 mature individuals in the National Chambal Sanctuary (Shaikh and Mendis 2019, Singh and Sharma 2018), 450 mature individuals on the River Ganga (A. Kumar in litt. to Parveen Shaikh 2019), 160-230 mature individuals along the River Mahanadi (Debata et al. 2019) and 50 mature individuals in the Son Gharial Sanctuary (P. Shaikh in litt. 2019). Additional breeding birds are thought to still occur in Pakistan, though we lack recent information and even in Threatened Birds of Asia there are few post 1980 records (BirdLife International 2001). In Myanmar there may be very few pairs (one seen in the Gulf of Mottama in 2020 may have been transitory [Chowdhury 2020]). In Bangladesh there are a small number of pairs that probably breed annually (dependent on river conditions) close to the Indian border along the Padma River (Kabir et al. 2016).
During the non-breeding season, birds in India disperse widely, but a small number of sites hold congregations of over 100 birds, totalling c. 850 individuals (eBird 2019, P. Shaikh in litt. 2020). While there is a wide scatter of additional records, these are of only single or small groups of birds. Given the long distances individuals appear to travel, few individuals may be involved in these multiple sightings and the number of additional birds is suggested to be fewer than 300 individuals. In Bangladesh, birds are more concentrated in a handful of sites, with 1,610 individuals recorded during surveys by the Bangladesh Spoon-billed Sandpiper Conservation Project (Chowdhury et al. 2020) and the Asian Waterbird Census (S. Mohsanin in litt. 2020). A small number of additional birds may be present along the Padma River and potentially elsewhere in the Meghna Delta, but much of the area has been searched without success. Consequently, the estimated winter total in Bangladesh is 1,700 individuals, and the overall minimum winter population is estimated at 2,550-2,850 individuals. If we assume that two-thirds of these are mature individuals, this gives an estimate of 1,700 – 1,900 mature individuals. This appears to be in reasonable agreement with the breeding estimate, assuming that there are an additional few hundred mature individuals breeding (or attempting to breed) at undiscovered sites.
From the two figures, the total estimated global population is placed at between 1,500 – 2,000 mature individuals. This is likely to be slightly precautionary. The key threats are nest predation and disturbance which drive low reproductive output, rather than adult mortality, such that there may be a higher proportion of adults in the population than the two-thirds assumed.
Indian Skimmer is facing a high number of threats throughout its range. Damming of rivers, water abstraction and sand mining have reduced water levels, allowing predators, people and cattle to access breeding islands (Shaikh et al. 2018, Shaikh and Mendis 2019). Major causes for nest failure are the predation of eggs and chicks by free-ranging dogs, nest loss through trampling by cattle, as well as anthropogenic disturbance, which are at very high levels in parts of the range (Debata et al. 2019, Shaikh and Mendis 2019, P. Shaikh in litt. 2020). Sand mining may also impact the actual formation of the islands, reducing available habitat area and quality. Stochastic events including sand storms, or exceptional rainfall can cause the failure of whole colonies (Rajguru 2017, Shaikh et al. 2018, Debata 2019). A large historical population would be buffered against these effects, but the alarmingly small overall population is now at risk of significant losses from each event.
In the light of this newly estimated population size, the species is here re-assessed against all Red List Criteria:
Criterion A – The previous population estimate was 6,000 – 10,000 individuals (Wetlands International 2012), roughly equating to 4,000 – 6,700 mature individuals, which was largely based on the direct count of 5,542 individuals during the Asian Waterbird Census in 2001 (Li and Mundkur 2004). That count has now been slightly revised to 5,532 (T. Mundkur in litt. 2020), but remains the relevant high count from which to assess population reduction. Using the counted number as a minimum estimate for the global population in 2001 (i.e. 5,532 individuals) and the minimum bound of the individuals estimate given above (i.e. 2,550 individuals), results in an estimated population reduction of 51.1% over the course of the past three generations (17.6 years, as the species has an estimated generation length of 5.85 years after Bird et al. 2020)*. As the threats impacting the species have not been mitigated, this rate of reduction is projected to continue into the future. If these numbers do indeed represent the best information we have, then the species meets the threshold for listing as Endangered under Criterion A2ac+3bc+4abc.
Criterion B – The Extent of Occurrence (EOO) from a Minimum Convex Polygon around the breeding/resident range is 5,030,000km2, and therefore does not approach the thresholds for listing as Vulnerable under Criterion B1. An estimate of the Area of Occupancy (AOO) has not been made, but even within the more restricted occupancy range during the breeding season, calculating the area occupied using a 2×2 km grid appears very likely to exceed the threshold for listing as threatened under criterion B2, as the breeding sites are spread over a relatively large area. In addition, the primary threats facing the species result in reduced reproductive success, such that the number of locations** is likely to be considerably higher than the threshold for listing as threatened. As such, Indian Skimmer would be considered Least Concern under Criterion B.
Criterion C – The new population estimate meets the threshold for listing as Endangered under Criterion C (2,500 mature individuals). Further subcriteria are required for listing under this criterion.
The rate of continuing decline in the population based on the estimated population reduction (see Criterion A) is 37.9% over 2 generations (19% over one generation), exceeding the threshold for listing as Endangered under Criterion C1.
There is no evidence of extreme fluctuation in the number of mature individuals; however, the species is considered to occur as a single subpopulation, given the wide dispersal and fairly limited breeding areas. As such, Indian Skimmer also meets the threshold for listing as Endangered under Criterion C2a(ii).
Criterion D – The population and range size of the species exceed the thresholds for listing as threatened under this criterion, therefore the species qualifies as Least Concern under Criterion D.
Criterion E – To the best of our knowledge no quantitative analysis of extinction risk has been conducted for this species. Therefore, it cannot be assessed against this criterion.
It is proposed that Indian Skimmer (Rynchops albicollis)be listed as Endangered under Criteria A2ac+3bc+4abc; C1+2a(ii). Based on available information on the population sizes in 2001 and 2020 as well as on the current rate of decline, it appears that the species may have crossed the threshold for listing as Endangered under Criterion C during the period 2012-2016, when the population size fell below the threshold of 2,500 mature individuals. We welcome any comments on the proposed listing and timing of change.
Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of its Red List status. Therefore, please make sure your comments are relevant to the discussion outlined in the topic. By submitting a comment, you confirm that you agree to the Comment Policy.
*Bird generation lengths are estimated using the methodology of Bird et al. (2020), as applied to parameter values updated for use in each IUCN Red List for birds reassessment cycle. Values used for the current assessment are available on request. We encourage people to contact us with additional or improved values for the following parameters; adult survival (true survival accounting for dispersal derived from an apparently stable population); mean age at first breeding; and maximum longevity (i.e. the biological maximum, hence values from captive individuals are acceptable).
**The term ‘location’ refers to a distinct area in which a single threatening event can rapidly affect all individuals of the taxon present, with the size of the location depending on the area covered by the threatening event. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).
An information booklet on the Red List Categories and Criteria can be downloaded here and the Red List Criteria Summary Sheet can be downloaded here. Detailed guidance on IUCN Red List terms and definitions and the application of the Red List Categories and Criteria can be downloaded here.
Bird, J.P., Martin, R., Akçakaya, H.R., Gilroy, J., Burfield, I.J., Garnett, S., Symes, A., Taylor, J., Şekercioğlu, Ç.H. & Butchart, S.H. (2020). Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology, online first view.
BirdLife International. 2001. Threatened birds of Asia: the BirdLife International Red Data Book. BirdLife International, Cambridge, U.K.
Chowdhury, S. U., Foysal, M., Prince, N. U., Mohsanin, S., Miron, M. K. & Alam, A. B. M. S. 2020. Discovery of a new wintering area for Indian Skimmer Rynchops albicollis in Bangladesh. BirdingASIA 32. (In Press)
Debata, S. 2019. Impact of cyclone Fani on the breeding success of sandbar-nesting birds along the Mahanadi River in Odisha, India. Journal of Threatened Taxa 11(14): 14895–14898.
Debata, S., T. Kar, H.S. Palei & K.K. Swain. 2019. Breeding ecology and causes of nest failure in the Indian Skimmer Rynchops albicollis. Bird Study 66: 243–250.
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IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. Gland, Switzerland and Cambridge, UK: IUCN. Available at www.iucnredlist.org/technical-documents/categories-and-criteria
Kabir, M. T., Chowdhury, S. U., Tareq, O., Alam, A. B. M. S., Ahmed, S., Shahadat, O. & Foysal, M. (2016) New breeding records of riverine birds in Bangladesh. BirdingASIA 26: 39-42.
Li, Z.W.D. & Mundkur, T. 2004. Numbers and distribution of waterbirds and wetlands in the Asia-Pacific Region. Results of the Asian Waterbird Census 1997–2001. Wetlands International, Kuala Lumpur.
Mohsanin, S. 2014. Survey of wintering Indian Skimmer Rynchops albicollis in Bangladesh. BirdingASIA 21: 105-106.
Rajguru, S. K. 2017 Breeding biology of Indian Skimmer Rynchops albicollis at Mahanadi River, Odisha, India. Indian BIRDS 13: 1–7.
Shaikh, P.A., Mendis, A., Luis, J., Das, D.K. & Surve, S. (2018). Status and distribution of Indian Skimmer Rhynchops albicollis in the National Chambal Sanctuary, India. Final Report submitted to BirdLife International.
Shaikh, P.A. & Mendis, A. 2019. Status and distribution of Indian Skimmer Rynchops albicollis breeding population in the National Chambal Sanctuary, India. Progress Report submitted to BirdLife International.
Singh, L. A. K. & Sharma, R. K. 2018. Sighting trend of the Indian Skimmer (Charidiformes: Laridae: Rynchops albicollis Swainson, 1838) in National Chambal Gharial Sanctuary (1984–2016) reflecting on the feasibility of long-term ecological monitoring. Journal of Threatened Taxa 10(5): 11574-11582.
Wetlands International. 2012. Waterbird Population Estimates. http://wpe.wetlands.org.