This discussion was first published on Nov 30 2010 as part of the 2010-2011 Red List update.
Initial deadline for comments: 31 January 2012.
Semipalmated Sandpiper Calidris pusilla is listed as Least Concern on the basis that it does not approach the thresholds for Vulnerable under any of the IUCN criteria. The species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence less than 20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be negative, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (at least a 30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (fewer than 10,000 mature individuals with a continuing decline estimated to be at least 10% over ten years or three generations, or with a specified population structure).
Recent population trends appear to have been negative for this species in many areas, prompting Morrison et al. (2006) to lower the previous population estimate from c.3.5 million to c.2 million. This adjustment was based on the assumptions of an annual rate of decline of 5% in 75% of the North American population, following the results of mark-recapture work in the Bay of Fundy (Hicklin and Chardine unpubl. data in Morrison et al. 2006). The new estimate, however, was later found to be deflated by a lack of data from western and interior regions, and was corrected to over 2.2 million following the extrapolation of densities calculated for breeding populations in the Arctic (per A. Lesterhuis in litt. 2009).
In an analysis of data from the Maritimes Shorebird Survey and the International Shorebird Survey gathered in central and eastern North America, Bart et al. (2007) detected an annual decline of 4% in the numbers of C. pusilla in the North Atlantic region and a 1.7% decline per year in the Midwest. This may not indicate a decline in the total population as once again western populations were not covered and the species could have shifted its migration routes or timing (Bart et al. 2007), although the slight decline in the Midwest region suggests this is unlikely to have been a factor.
Aerial surveys conducted in December 2008 along the coasts of Suriname and French Guiana suggest that the non-breeding population of C. pusilla in this region could have declined by c.80% since the early 1980s, from c. 2 million to c.400,000, which could be serious given that the region may support c.85% of the population of this species wintering on the coast of South America (D. Mizrahi in litt. 2009). So far, the possibility that the species is shifting its geographical preferences during the non-breeding season cannot be ruled out; however, it has been stated that such a shift does not appear to have taken place (D. Mizrahi in Murray 2009). Fieldwork undertaken in French Guiana and Suriname during January 2009 revealed that the hunting of shorebirds, which is legal in French Guiana but illegal in Suriname, is widespread and thus a potential threat to C. pusilla. A survey carried out in Suriname during 2006 suggested that hunters there take thousands of C. pusilla (A. Spaans per D. Mizrahi in litt. 2009). Poaching in Suriname may have increased over the last c.20 years owing to improvements in weaponry and transportation. Another potential threat is the harvesting of horseshoe crabs in Delaware Bay, an area which reportedly sees the passage of c.60% of the total population of C. pusilla during the spring migration (D. Mizrahi in Murray 2009). The species may be suffering due to a decline in the abundance of horseshoe crab Limulus polyphemus eggs, on which they feed during their northward migration; however, the impact of horseshoe crab fishing on shorebirds is a point of contention (Murray 2009).
There is considerable uncertainty inherent in drawing conclusions from regional population trends for a widespread species such as C. pusilla; however, it remains necessary to estimate the likely overall trend for the species. If the population is found to have declined at a rate approaching 30% over 22 years (estimate of three generations) it may be eligible for uplisting to Near Threatened under the A criterion. The species would likely qualify for at least Vulnerable if the estimated overall decline is at least 30% over 22 years. Up-to-date information is requested on this species, in particular the likely population trend and the severity of threats.
Bart, J., Brown, S., Harrington, B. and Morrison, R. I. G. (2007) Survey trends of North American shorebirds: population declines or shifting distributions? J. Avian Biol.: 38: 73-82.
Morrison, R. I. G., McCaffery, B. J., Gill, R. E., Skagen, S. K., Jones, S. L., Page, G. W., Gratto-Trevor, C. L. and Andres, B. A. (2006) Population estimates of North American shorebirds, 2006. Wader Study Group Bull.: 111: 67-85.
Murray, B. T. (2009) Turns out the red knot is not alone in its plight. The Star-Ledger: 1 February 2009. Newark, NJ.
The following manuscript was sent by Brad Andres on 23 January 2012: Calidris pusilla Andres et al. in press (Andres, B. A., C. L. Gratto-Trevor, P. Hicklin, D. Mizrahi, R. I. G. Morrison, and P. A. Smith. 2012. Status of the Semipalmated Sandpiper. Waterbirds 35: in press.)
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