New estimates of the size and trend of the world population of the spoon-billed sandpiper using three independent statistical models

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Green, RE 
Syroechkovskiy, EE 
Anderson, GQA 
Chang, Q 
Chowdhury, SU 

A single formal estimate of the size of the world population of the Critically Endangered Spoon-billed Sandpiper Calidris pygmaea has been published. This used a Lincoln-Petersen method, which combined a global mark-resighting analysis with a scan survey to estimate the proportion of birds with individual marks observed at a post-breeding moult and migration stopover site in Jiangsu Province, China. We report nine further repetitions of this procedure, which we call Method A, giving ten world population estimates in all, during the 6-year period 2014–2019. Four of these estimates use scan surveys from Jiangsu in the post-breeding adult moult period and six are from the non-breeding season (November–February) at three widely-separated sites in Bangladesh, Myanmar and South China. The weighted mean world population size at the end of the breeding season, based upon all ten surveys, was 490 mature individuals (95% C.L. 360–620) and 773 individuals of all ages (95% C.L. 569–978), which is similar to the single previous Method A estimate (420 mature individuals), but considerably more precise. We also report results from two independent but low-precision methods: one based upon published non-breeding season counts and the non-breeding season localities of satellite-tagged birds (Method B) and the other based upon mark-recapture analysis of birds marked as unfledged chicks and recaptured as migrating juveniles (Method C). These two methods gave estimates within the range 471 to 922 mature individuals, depending upon assumptions. The trend of Method A population size estimates with time during the short study period was a decline at a mean rate of 8% per year, but this did not differ significantly from zero (no change). The precision of this estimate of population trend was low, but its rate is of similar magnitude to the 9% per year decline during 2009–2016, derived from surveys of the local population at the most important known non-breeding season site in Myanmar. Hence, although the rapid population decline indicated by surveys of breeding populations observed prior to 2009 (mean 26% decline per year) has probably slowed as a result of conservation efforts, our results indicate that the species should continue to be listed as Critically Endangered.

38 Economics, 31 Biological Sciences, 3801 Applied Economics
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Wader Study
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International Wader Study Group
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We thank the students of Nanjing Normal University who have helped in the ringing of Spoon-billed Sandpipers and other shorebirds in Jiangsu Province, China: Zhao Fangzheng, Ge Xiaohui, Hu Dongfang, Liu Wei, Zhang Yi, Chen Peng, Tai Deyun, Wu Yuhao, Xu Xue, Yao Wenjia, Wang Hao, Qian Nven; We thank the researchers from the Jiangsu Academy of Forestry: Ding Jingjing, Wang Xuan. We are grateful to the China Bird Banding Center, which supports the banding programme in China. Data collection was partly supported by The Biodiversity Investigation and Assessment program (2019–2023) of the Ministry of Ecology and Environment of China. Research and conservation work by BirdsRussia in Chukotka and Kamchatka was supported by RSPB, NABU, MHS, WWT, Chukotka administration and many other funding sources. The work of E. Lappo was partly supported by Basic Research Program (budgetary funds), project No.0148-2019-0007. Russian authors are thankful to all BirdsRussia team members, including numerous volunteers from abroad, who helped with nest searching and supported the catching and individual marking of birds. Svetlana and Roman Belogorodtsevy and other people of Meinypil’gyno are thanked for their help during our fieldwork. Richard Hearn, Kane Brides and Pyae-Phyo Aung made valuable contributions to the fieldwork. We thank all the surveyors and photographers who have undertaken surveys or sent in records of marked birds and Vivian Fu, Ding Li Yong and Paul Insua-Cao for detailed advice on past survey locations. We thank Nicola Crockford and Christoph Zöckler for advice and comments. We are grateful to Paul Howey of Microwave Telemetry Inc. for developing the miniature satellite tags used in this study and responding to our requests for variations of the design. We thank the (Animal Welfare) Ethics Advisory Committee of the Royal Society for the Protection of Birds for scrutinising our application to attach satellite tags to Spoon-billed Sandpipers.