Initial deadline for comments: 31 January 2012.
Long-tailed Duck Clangula hyemalis is a widespread circumpolar species that breeds mainly in the Arctic tundra and winters generally to the south, mainly far offshore. It is currently listed as Least Concern because it was not thought to approach the thresholds for Vulnerable under any of the IUCN Red List criteria.
This species has an extremely large range (Extent of Occurrence [EOO] in breeding season estimated at c.9.55 million km2; wintering EOO >1.7 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. 6.5 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).
However, a new publication, comparing the results of winter surveys in the Baltic Sea in 1992-1993 and 2007-2009, indicates that the species has declined significantly there (Skov et al. 2011). An estimated total of c.4,272,000 individuals was counted there in 1992-1993, falling to c.1,486,000 individuals in 2007-2009, which suggests that a decline of c.65% has occurred over a period of 16 years. This extrapolates to a decline of c.83% over the last three generations, estimated by BirdLife to be 27 years (based on a generation length of c.9 years). This decline appears to be on-going, with Swedish survey results from 2011 indicating a decline of c.80% since 1992-1993 (K. Larsson in litt. 2011).
The Baltic Sea is the most important wintering area for this species in the world, holding most of the northern European and western Siberian breeding populations. The c.4.3 million birds recorded there in 1993 represented c.66% of the latest (but obviously now outdated) global population estimate of c.6.5 million birds (Wetlands International 2006). The decline detected in the Baltic Sea therefore has global significance. The current trend of the small component of the European population that winters outside the Baltic (c.300,000 birds) is unknown, but there is some evidence that it may also be declining (e.g. in the UK: Holt et al. 2011, Musgrove et al. 2011).
North America holds the second largest population (c.1 million birds; Wetlands International 2006). The North American Waterfowl Breeding Population Survey (NAWBPS) traditional area survey suggests that an annual change of -5.3% occurred in the species’s population from 1973 to 1997 (Sea Duck Joint Venture 2003). The Mid-winter inventory (US Atlantic coast) shows a decline of -1.1% per year during 1976-1997. The Atlantic Coast Sea Duck Survey shows no statistically significant trend during 1991-1999, but the data do suggest a decline. In contrast, the Arctic Coastal Plain Survey indicates a relatively stable breeding population since 1986 and the Yukon-Kuskokwim Delta Coastal Zone Survey shows slowly increasing numbers since 1988. The Atlantic flyway Christmas Bird Count (CBC) data show no trend during 1973-1995 (Sea Duck Joint Venture 2003). Overall, however, CBC data indicate an annual population change of -1.9% between 1965 and 2005, across c.70% of the species’s range in North America (Butcher and Niven 2007), suggesting that a decline of c.54% has occurred over 40 years, or a c.40% decline over 27 years (three generations).
No trend data are available for the third largest population (c.500,000–1,000,000 birds), which breeds in eastern Siberia and winters off eastern Asia. The fourth and smallest population (c.100,000–150,000 birds), which breeds in Greenland and Iceland and winters in the north Atlantic, is poorly monitored and trends are uncertain, although it may have been stable until the 1990s (Wetlands International 2006).
It is possible that the lower numbers recorded in the Baltic (and possibly also in North America) relate not to a population decline, but to changes in the species’s winter distribution (e.g. Zipkin et al. 2010). 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. Long-tailed Duck may have been affected by this phenomenon, but there is currently no evidence to suggest that the c.2.8 million birds ‘missing’ from the south-central Baltic are now wintering further north, either in the northern Baltic (Skov et al. 2011) or in, for example, the White Sea or Barents Sea off north-western Russia.
There is, however, evidence that the species is struggling on its Arctic breeding grounds. The results of autumn migration monitoring at various Baltic sites show that juveniles now represent a very low proportion of the population (e.g. Hario et al. 2009, Ellermaa et al. 2010), indicating that insufficient young are being raised to compensate for adult mortality. The breeding success of this (and other) species seems to have declined since the mid-1990s, when the formerly distinctive 3-4 year cycle in the abundance of Arctic rodents collapsed, probably due to climate change. With fewer rodents around, Arctic predators now take a heavier toll on breeding birds every single year, instead of only once every 3-4 years.
In turn, these missing recruits may have increased the impacts of oil pollution, hunting, bycatch and other threats on adult Long-tailed Ducks in the Baltic (e.g. Larsson & Tydén 2005). As expressed by Hario et al. (2009): “In long-living species, such as seaduck, the population growth rate is much more sensitive to variations in adult survival than to variations in fecundity or immature survival. With a missing “floating” element of the population, there are not enough debut breeders entering the breeding stock to fill the gaps created by increased adult mortality. This may be the biggest difference between the current dynamics of the Long-tailed Duck compared to the situation in past, when winter mortality was heavy, but the lemming cycles on the breeding grounds still existed, which allowed the population to recover”.
Taking the 27-year decline rates calculated for the Baltic and North American populations, and assuming that the two other smaller populations have remained stable, the species’s global population may be declining at a rate of more than 50% over three generations, which would qualify the species for uplisting to Endangered 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 eastern Asia, Greenland, Iceland and North America.
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.
Ellermaa, M., Pettay, T., & Könönen, J. (2010) [Autumn migration in Põõsaspea Cape in 2009.] Hirundo 23(1): 21-46. (in Estonian, with English summary) http://www.eoy.ee/hirundo/sisukorrad/2010_1/Ellermaa_etal_23_1.pdf
Hario, M., Rintala, J. & Nordenswan, G. (2009) [Dynamics of wintering long-tailed ducks in the Baltic Sea – the connection with lemming cycles, oil disasters, and hunting.] Suomen Riista 55: 83-96. (in Finnish, with English summary)
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.
Larsson, K. & Tydén, L. (2005) [Effects of oil spills on wintering Long-tailed Ducks Clangula hyemalis at Hoburgs bank in central Baltic Sea between 1996/97 and 2003/04.] Ornis Svecica 15: 161-171. [in Swedish, with English summary] http://www.nioz.nl/public/mee/birds/0483.pdf
Musgrove, A. J., Austin, G. E., Hearn, R. D., Holt, C. A., Stroud, D. A. and Wotton, S. R. (2011) Overwinter population estimates of British waterbirds. British Birds 104: 364-397.
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.
Zipkin, E. F., Gardner, B., Gilbert, A. T., O’Connell, A. F., Royle, J. A. and Silverman, E. D. (2010) Distribution patterns of wintering sea ducks in relation to the North Atlantic Oscillation and local environmental characteristics. Oecologia 163: 893-902.
The following input from Dr. Gennady Grishanov was forwarded to us on 30 January 2012: Clangula hyemalis Grishanov Jan12
The following letter was received on 31 January 2012; Clangula hyemalis Lehikoinen et al. Jan12
Long-tailed Duck revised global three-generation decline estimate – added 14/2/12 (see comment posted by Andy Symes on 14/2/12 for background)