Bar-tailed Godwit (BirdLife factsheet) breeds across the Arctic from northern Europe through Siberia to Alaska, wintering along the coasts of western Europe, Africa, the Middle East, South and Southeast Asia, Australia and New Zealand.
Globally, it has an extremely large range in both the breeding season and in winter, and hence does not approach the thresholds for Vulnerable under the range size criteria (B and D2). Its population size is also extremely large (999,000–1,049,000 individuals; Wetlands International 2015), and hence does not approach the thresholds for Vulnerable under the population size criteria (C and D1). Therefore, the only potentially relevant criterion is A, which relates to reductions in population size. Until recently, the population was thought to be declining slowly, but not sufficiently rapidly to approach the threshold for listing as Vulnerable under criterion A (at least a 30% decline over ten years or three generations, whichever is longer).
The following summary is based on that in Wetlands International (2015):
|Population||Breeds / winters||Size (individuals)||% total||Trend|
|lapponica||N Europe / W Europe||120,000||11-12%||Stable/Increasing (BirdLife International 2015)|
|taymyrensis||W Siberia / W & SW Africa||500,000||48-50%||Moderately rapid decline? (c23-27% in three generations; extrapolated from Van Roomen et al. 2014)|
|taymyrensis||C Siberia / S & SW Asia & E Africa||100,000-150,000||10-14%||Unknown (Delany et al. 2009)|
|menzbieri & (anadyrensis)||N Siberia / SE Asia to Australia||146,000||14-15%||Very rapid decline (79.1% in three generations; Garnett 2015)|
|baueri||E Siberia & W Alaska / China to Australia & New Zealand||133,000||13%||Rapid decline (30.2% in three generations; Garnett 2015)|
|Total||Global||999,000-1,049,000||Moderately rapid/rapid decline?|
Trend in Europe (lapponica):
The breeding population trend is unknown. The wintering population trend is increasing (BirdLife International 2015).
Trend in W Africa (taymyrensis):
Van Roomen et al. (2014) report an estimated decline based on wintering counts for the period of 2003-2014, also long-term decline for the period of 1979-2014. Total wintering numbers were estimated at 745,803 in the 1980s, 516,920 in the 1990s and 497,433 (rounded to 500,000) in the 2010s.
Trend in East Africa (taymyrensis):
Reported as unknown by Wetlands International (2015). A large proportion of this population winters at Bar al Hikman, Oman (eg. 87,187 individuals in Dec 2013; de Fouw in litt. to Wetlands International).
Trend in East Asian-Australasian Flyway (menzbieri and baueri):
c.27-28% of the global population uses the flyway. BirdLife Australia’s Threatened Species Committee, which applies the IUCN Categories and Criteria at the national level, recently recommended the uplisting of the subspecies L. l. menzbieri from Vulnerable to Endangered (under criterion A2bc+3bc+4bc) in Australia (Garnett 2015), and the recommendation was subsequently accepted by the BirdLife Australia Research and Conservation Committee. The subspecies L. l. baueri remains classified as Vulnerable in Australia. The proposal was based on a detailed analysis of all monitoring data collected on shorebirds around Australia and New Zealand in the last 30 years (Studds et al. in prep) – see extract here:
|Taxon||Annual rate of decline||Generation time||Loss over three generations||Action Plan status 2010||Recommended status 2015|
|L. l. menzbieri||-0.061||8.9||-79.1||Vulnerable||Endangered|
|L. l. baueri||-0.014||8.9||-30.2||Vulnerable||Vulnerable|
The analysis used Bayesian binomial mixture models of non-breeding count data throughout Australia and New Zealand to estimate trends for subpopulations thought to follow different migration routes and summarized these estimates to yield flyway-level trends. Count data for each taxon were acquired from local and national databases in Australia and New Zealand. Many counts began in the early 1980s, but several key sites initiated counts in the 1990s.
For shorebirds of the East Asian-Australasian Flyway there is considerable concern that loss of intertidal stopover habitat in the Yellow Sea region of East Asia is driving population declines (Amano et al. 2010; Yang et al. 2011). Up to 65 percent of intertidal habitat in the Yellow Sea has been lost over the past 50 years, and habitat is currently disappearing at a rate of >1 percent annually owing to reclamation for agriculture, aquaculture, and other development (Murray et al. 2014). Current rates of Yellow Sea habitat loss seem likely to continue or accelerate owing to projected human population growth, much of it concentrated along the margins of the Yellow Sea.
Further evidence of genuine very rapid recent decline in the population of menzbieri comes from a study of adult survival in this species, Red Knot and Great Knot along the East Asian-Australasian Flyway. Whereas the survival in NW Australia in late winter remained constantly high, the survival during the time away from Australia started to decline in 2011. With an annual survival rate for Bar-tailed Godwit during 2011-2012 of 0.69, the study predicts that this population will halve within four years, and that only the immediate protection and safeguard of suitable staging grounds in the Yellow Sea region, during both northward and southward migration, may now help to prevent extinction (Piersma et al. submitted).
Summary and proposal
Despite the fact that population trends vary between different flyway populations, the overall picture seems to indicate that the species is declining by around 29-37% over three generations (27 years), depending on the interpretation of the data from West Africa in van Roomen et al. (2014). This assumes stability in the only population where the trend is unknown (taymyrensis wintering in the Middle East and East Africa) – were this to be declining the overall rate of decline would increase further. These data together suggest the species most likely warrants uplisting to Vulnerable under criterion A2bc+3bc+4bc.
Comments on the population size and trend estimates and threats to the species are welcomed, in particular from parts of the range where data are limited.
Amano, T., T. Szekely, K. Koyama, H. Amano, and W. J. Sutherland. 2010. A framework for monitoring the status of populations: An example from wader populations in the East Asian-Australasian flyway. Biological Conservation 143:2238-2247.
Delany, S.; Scott, D.; Dodman, T.; Stroud, D. 2009. An atlas of wader populations in Africa and Western Eurasia. Wetlands International, Wageningen, The Netherlands.
Garnett, S. T. 2015. BirdLife Australia Threatened Species Committee report to RACC. 23rd January 2015. Unpublished report.
Murray, N. J., R. S. Clemens, S. R. Phinn, H. P. Possingham, and R. A. Fuller. 2014. Tracking the rapid loss of tidal wetlands in the Yellow Sea. Frontiers in Ecology and the Environment 12:267-272 http://www.fullerlab.org/wp-content/uploads/2014/05/Murray-et-al-2014.pdf
Piersma, T. et al. submitted. Simultaneous declines in summer survival of three shorebird species signals a flyway at risk. PLOS Biology
Studds, C. E. et al. in prep. Dependence on the Yellow Sea predicts population collapse in a migratory flyway.
Van Gils, J. & Wiersma, P. (1996). Bar-tailed Godwit (Limosa lapponica). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.) (2014). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/53890 on 23 July 2015).
van Roomen, M., van Winden, E. & Langendoen, T. (2014) The assessment of trends and population sizes of a selection of waterbird species and populations from the coastal East Atlantic Flyway for Conservation Status Report 6 of The African Eurasian Waterbird Agreement. http://www.wetlands.org/Portals/0/EAF_selection%20of%20species2014_2.doc.pdf
Wetlands International (2015). “Waterbird Population Estimates” . Retrieved from wpe.wetlands.org on Wednesday 22 Jul 2015
Yang, H. Y., B. Chen, M. Barter, T. Piersma, C. F. Zhou, F. S. Li, and Z. W. Zhang. 2011. Impacts of tidal land reclamation in Bohai Bay, China: ongoing losses of critical Yellow Sea waterbird staging and wintering sites. Bird Conservation International 21: 241-259