Initial deadline for comments: 31 January 2012.
Greater Scaup Aythya marila breeds in tundra and moorland in northernmost Europe, Asia and North America, and winters in shallow coastal waters and occasionally inland water bodies south of its breeding grounds. The species is currently listed as Least Concern on the basis that it was not thought to approach the thresholds for Vulnerable under any of the IUCN criteria.
This species has an extremely large range (Extent of Occurrence [EOO] in the breeding season estimated at c.7.83 million km2, wintering EOO c.4.98 million km2) and hence does not approach the thresholds for Vulnerable under the range size criteria (B and D2: EOO of 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). The population size is also extremely large (c.1.2 million individuals; Wetlands International 2006), and hence does not approach the thresholds for Vulnerable under the population size criteria (C and D1: 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). Therefore, the only 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).
An analysis of Christmas Bird Count data collected since the mid-1960s suggests that an annual population change of -3.4% has occurred across c.85% of the species’s range in North America, indicating a 75% decline between 1965-1966 and 2005-2006 (Butcher and Niven 2007), and suggesting a decline of c.57% over the last three generations, estimated by BirdLife to be c.25 years (based on a generation length of c.8.2 years), assuming an exponential trend. In addition to this rapid decline, survey results from the Baltic Sea suggest that the species has declined there as a wintering species, from an estimated 146,000 individuals in 1992-1993 to 127,000 individuals in 2007-2009, suggesting a decline of c.13% in c.16 years (Skov et al. 2011). This is equivalent to a decline of c.20% over the last three generations.
Together, the north-west European and North American populations comprise around two-thirds of this species’s global population (Wetlands International 2006), so these declines are of potentially global significance. The rates of decline recorded in North America (c.44% of the estimated global population) and the Baltic Sea (c.24% of the estimated global population) suggest that overall the species has declined by at least c.30% over three generations, assuming that the other populations (c.32% of the estimated global population) are stable. No trend information is available for these other two populations (western Siberia/Black and Caspian Seas; eastern Siberia/East Asia), so further information and data are requested from other parts of its range, especially East Asia.
Under criterion A, an overall decline approaching 30% (typically 20-29%) over 25 years would probably qualify the species for Near Threatened, while a decline of at least 30% over 25 years could make it eligible for uplisting to Vulnerable.
Butcher, G. S. and Niven, D. K. (2007) Combining Data from the Christmas Bird Count and Breeding Bird Survey to Determine the Continental Status and Trends of North American Birds. Ivyland, PA: National Audubon Society.
Skov, H., Heinänen, S., Žydelis, R, Bellebaum, J., Bzoma, S., Dagys, M., Durinck, J., Garthe, S., Grishanov, G., Hario, M., Kieckbusch, J. K., Kube, J., Kuresoo, A., Larsson, K., Luigujoe, L., Meissner, W., Nehls, H. W., Nilsson, L., Petersen, I. K., Roos, M. M., Pihl, S., Sonntag, N., Stock, A. and Stipniece, A. (2011) Waterbird Populations and Pressures in the Baltic Sea. TemaNord 2011: 550. Copenhagen, Denmark: Nordic Council of Ministers.
Wetlands International (2006) Waterbird population estimates. Fourth edition. Wageningen, The Netherlands: Wetlands International.
The following letter was sent by Michael L. Szymanski on behalf of the Central Flyway Council on 30 January 2012: Aythya marila Central Flyway Jan12
The following letter by Jean-Michel DeVink, with support from members of the Canadian Wildlife Service’s Waterfowl Committee, was received on 30 January 2012: Aythya marila DeVink Jan12
The following letter was received on 31 January 2012: Aythya marila Lehikoinen et al. Jan12
The following information was received on 14 February 2012: Greater ScaupStatus 14Feb12 J Barclay