Red Knot (BirdLife factsheet) is a long-distance migrant shorebird, with six Arctic-breeding subspecies:
- C. c. canutus – CN Siberia, in Taymyr Peninsula and possibly Yakutia; winters in W & S Africa and S Asia.
- C. c. piersmai – New Siberian Is; winters in NW Australia.
- C. c. rogersi – Chukotskiy Peninsula and possibly areas farther W; winters in Australasia.
- C. c. roselaari – Wrangel I (off NE Siberia) and NW Alaska; winters primarily in western Mexico.
- C. c. rufa – Canadian low Arctic; winters on coasts of south Florida, Texas, northern Brazil and southern South America.
- C. c. islandica – islands of Canadian high Arctic and N Greenland; winters in W Europe.
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 (891,000–979,000 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)||% of total||Trend and sources|
|islandica, NE Canada & Greenland/Western Europe||500,000-565,000||55-59%||Uncertain|
|canutus, Northern Siberia/West & Southern Africa||250,000||26-28%||Long-term decline|
|piersmai||50,500-62,000||5-7%||Very rapid decline (57.4% in three generations; Garnett 2015)|
|roselaari||17,000||2%||Uncertain; possible decline (Andres et al. 2012)|
|rogersi||48,500-60,000||5-7%||Very rapid decline (57.4% in three generations; Garnett 2015)|
|rufa||25,000||3%||‘Significant decline’ during 2000s (Andres et al. 2012; USFWS 2014).|
|Global||891,000-979,000||Moderately rapid decline?|
Long-term trend based on International Waterbird Census data is fluctuating; short-term (2003-2012) is moderate decrease (Nagy et al. 2014).
However the European Red List suggests strong increase (1.4-2.95% p.a.) in the short-term (2000-2012) and moderate increase (0.29-0.56%) in the long-term (1980-2012) (BirdLife International 2015).
Using different trend analysis method on the IWC data, van Roomen et al. (in prep) found stable/fluctuating trend both in the short- and in the long-term (Wetlands International 2015). Owing to these conflicting datasets, the overall trend is therefore uncertain.
Based on mid-winter counts, this subspecies underwent a large decrease both in the long- and in the short-term (1979-2014 and 2003-2014, respectively) according to van Roomen et al. (2014). This equates to a decline of some 37% over three generations.
Uncertain; possible decline (Andres et al. 2012).
“Despite the recent variability, numbers remain much lower than the 1980s and 1990s (Dey et al. 2011). Clearly, trends in C. c. rufa demonstrate an overall significant decline in the last decade in all three wintering populations” (Andres et al. 2012).
Average counts for Tierra del Fuego between 1985-2000 (52,244) dropped by about 75% by 2011-2013 (11,385). Comparing four different time periods, average counts in Delaware Bay declined about 70% overall from 59,946 (1981-1983) to 18,387 (2005-2014), with average counts between those years including 46,886 (1986-1994) and 34,060 (1995-2004) (USFWS 2014). If the population of this form has declined in line with data from Delaware Bay and Tierra del Fuego this equates to a c.55% in three generations.
piersmai and rogersi:
c.10-14% 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 uplisting 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 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:
|Annual rate of decline||Generation time||Loss over three generations||Action Plan status 2010||Recommended status 2015|
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 comes from a study of adult survival in this species, Great Knot and Bar-tailed Godwit 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 Red Knot during 2011-2012 of 0.62, the study predicts that the flyway population of Red Knot will halve within four years (Piersma et al. submitted).
Summary and proposal
Assuming stability of islandica and roselaari, and three-generation declines of 37% in canutus; 57% in piersmai and rogersi, and 55% in rufa, an overall decline of around 25% in three generations may be inferred. This would imply that the species could warrant listing as Near Threatened. However, given the uncertainties outlined above, particularly in relation to the population of islandica (accounting for 55-59% of the global population of the species), it may be appropriate to infer a more conservative rate of decline. Conversely, if there is evidence for decline in populations currently assumed to be stable, the overall rate of decline may be even higher.
Comments on all 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.
Andres, B.A., Smith, P.A., Morrison, R.I.G., Gratto-Trevor, C.L., Brown, S.C. & Friis, C.A. 2012. Population estimates of North American shorebirds, 2012. Wader Study Group Bull. 119(3): 178–194.
Dey, A.D., L.J. Niles, H.P. Sitters, K.S. Kalasz & R.I.G. Morrison. 2011. Update to the status of the Red Knot (Calidris canutus) in the Western Hemisphere, April 2011. Unpubl. report, Manomet Center for Conservation Sciences, Manomet, MA, USA. http://www.whsrn.org/sites/default/files/file/Red_Knot_status_update_2011_Dey_et_al_11_05-28.pdf
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
Nagy, S., Flink, S., Langendoen, T. (2014) Waterbird trends 1988-2012: Results of trend analyses of data from the International Waterbird Census in the African-Eurasian Flyway. Wetlands International, Ede. www.wetlands.org/Portals/0/TRIM Report 2014_10_05.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.
USFWS. (2014). U.S. Fish and Wildlife Service Protects the Rufa Red Knot as Threatened Under Endangered Species Act: Questions and Answers http://www.fws.gov/northeast/redknot/pdf/DRAFT_QAs_red_knot_finallisting_120814_FINAL.pdf
Van Gils, J. & Wiersma, P. (1996). Red Knot (Calidris canutus). 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/53922 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