Initial deadline for comments: 31 January 2012.
BirdLife species factsheet for Black Scoter (prior to the taxonomic change)
Black Scoter Melanitta nigra has been split into M. nigra and M. americana following a review of recent literature (Livezey 1995, Garner et al. 2004, Sangster et al. 2005, Collinson et al. 2006, AOU 2010) and museum specimens by the BirdLife Taxonomic Working Group. Prior to this taxonomic change, the polytypic species M. nigra was listed as being of Least Concern on the basis that it was not thought to approach the thresholds for Vulnerable under any of the IUCN criteria.
Following the taxonomic change, both species are still regarded as having extremely large ranges and hence do 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). Their population sizes are also large (>530,000 individuals; Wetlands International 2006), and hence do 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, there was little evidence to suggest that populations of either taxa were declining 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).
There is now evidence of a rapid decline in the population of M. nigra (Skov et al. 2011), which breeds in western Siberia, Scandinavia, Iceland, Scotland and Ireland, and winters in the Baltic Sea and east Atlantic south to Mauritania (Wetlands International 2006). An analysis of the population trend in the Baltic Sea suggests that a decline of 47.4% occurred between 1988-1993, when a total of c.783,000 birds wintered there, and 2007-2009, when c.412,000 birds were counted (Skov et al. 2011). Extrapolation of these data suggests that this is equivalent to a decline of c.55% over three generations (23 years, based on a generation length of c.7.5 years; BirdLife International unpubl. data).
The Baltic Sea is (or at least was) the most important wintering area in the world for this species. The 783,000 birds recorded there in 1992-1993 represented just under half of the latest (but obviously now outdated) global population estimate of c.1,600,000 birds (Wetlands International 2006). The decline detected in the Baltic Sea population therefore has global significance. The current trend of the birds that winter outside the Baltic is largely unknown, but there is some evidence that these may also be declining, e.g. in the Netherlands (Hornman et al. 2011). The proportion of birds wintering in the Baltic Sea is believed to be linked to the breeding success of birds in Russia (Durinck et al. 1994 in Skov et al. 2011).
It is possible that the lower numbers recorded in the Baltic (and possibly elsewhere in north-western Europe) relate not to a population decline, but to changes in the species’s winter distribution. In recent decades, many waterfowl species have responded to global climate change by ‘short-stopping’, i.e. taking advantage of warmer conditions to winter closer to northern breeding areas than was previously possible. M. nigra may have been affected by this phenomenon, and there is some evidence for a slight northwards shift in the species’s distribution within the Baltic (Skov et al. 2011). However, this is not capable of explaining the whereabouts of the c.360,000 birds ‘missing’ from the Baltic. It is possible that some birds may now be wintering in the White Sea or Barents Sea off north-western Russia, but there is no evidence for this.
If the decline in the Baltic also applies to the rest of the species’s population, then globally it may be declining at a rate of more than 40% over three generations, which would qualify the species for uplisting to Vulnerable under criterion A. To permit a more comprehensive assessment, further and more recent information on the size and trend of the species’s population is requested for all parts of its range, but particularly from those countries along the North Sea and Atlantic coasts, which have held large wintering populations in the past.
This species is thought to be declining in western Alaska and to be stable on the Arctic coastal plain (per Sea Duck Joint Venture 2003). Numbers also appear to be declining in the Atlantic flyway, whereas no statistically significant population trend is apparent in the results of a fixed-wing aerial survey covering the Atlantic coast for the period 1991-1999 (Sea Duck Joint Venture 2003). Data from the US Fish and Wildlife Service–Canadian Wildlife Service breeding waterfowl survey indicate that the combined population of all three scoter species along survey transects in the western boreal forest may have declined by as much as 75% since the 1950s. Mid-winter inventory data do not indicate any trends on the Pacific coast and only weakly show a decline on the Atlantic coast. However, these surveys are said to track scoter populations poorly and all three species are combined in one count (Sea Duck Joint Venture 2003). An analysis of Christmas Bird Count data overall indicates an annual change of -1.26% between 1965-1966 and 2005-2006 across about half of the species’s range in North America (Butcher and Niven 2007), equating to a 40-year decline of c.50%, and thus suggestive of a c.32% decline over the last three generations, provisionally assumed to be 23 years, based on a generation length of c.7.5 years (BirdLife International unpubl. data), and an exponential trend.
However, trends are apparently unknown in far north-east Asia, where the species occurs east of Lena and numbers an estimated 300,000-500,000 birds or 12-24% of the estimated global population (see Wetlands International 2006), thus more information is required.
Further information is requested on population trends in these two newly-split species and comments are invited on whether the population of M. nigra is likely to have declined at a rate equivalent to at least 30% over the past three generations, and thus if it qualifies for listing as at least Vulnerable under criterion A. Under the same criterion a decline of at least 50% over three generations would qualify the species for Endangered, whereas a decline approaching 30% (typically 20-29%) would qualify the species for Near Threatened. Likewise, comments are invited on the population trend of M. americana, especially in East Asia.
American Ornithologists’ Union (2010) Fifty-first Supplement to the American Ornithologists’ Union Check-list of North American Birds. Auk 127: 726-744.
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.
Collinson, M., Parkin, D. T., Knox, A. G., Sangster, G. and Helbig, A. J. (2006) Species limits within the genus Melanitta, the scoters. British Birds 99: 183-201.
Garner, M., Lewington, I. and Rosenberg, G. (2004) Stejneger’s Scoter in the Western Palearctic and North America. Birding World 17: 337-347.
Holt, C. A., Austin, G. E., Calbrade, N. A., Mellan, H. J., Mitchell, C., Stroud, D. A., Wotton, S. R. and Musgrove, A. J. (2011) Waterbirds in the UK 2009/10: The Wetland Bird Survey. Thetford, UK: BTO/RSPB/JNCC.
Hornman, M., Hustings, F., Koffijberg, K., van Winden, E., SOVON Ganzen-en Zwanenwerk-groep and Soldaat, L. (2011) Watervogels in Nederland in 2008/2009. SOVON-monitoringrapport 2011/03, Waterdienst-rapport BM 10.24. SOVON Vogelonderzoek Nederland, Nijmegen.
Livezey, B. C. (1995) Phylogeny and Evolutionary Ecology of Modern Seaducks (Anatidae: Mergini). Condor 97: 233-255.
Sangster, G., Collinson, J. M., Helbig, A. J., Knox, A. G. and Parkin, D. T. (2005) Taxonomic recommendations for British birds: third report. Ibis 147: 821-826.
Sea Duck Joint Venture (2003) Species status report. http://www.seaduckjv.org/meetseaduck/species_status_summary.pdf
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 received on 31 January 2012:Melanitta nigra Lehikoinen et al. Jan12