The global population size and trend of Ferruginous Duck has been difficult to establish with confidence due to an apparent tendency to shift its breeding distribution in response to interannual fluctuations in water levels across a very large range. Declines have been documented in parts of the range, but evidence from the larger Asian populations is mixed. As a result, the species is currently considered Near Threatened.
For the relatively small proportion of the global population that winters in Europe, the trend reported in the 2015 European Red List of Birds was increasing within the EU 27 and stable for the whole of Europe (BirdLife International 2015). In addition, in China the species is expanding eastwards and increasing, with recent estimates of the breeding population of 1,500-2,000 pairs, and 6,000-8,000 wintering individuals (Zhao and Maming 2014). The suggestion that these two populations may be stable would indicate that any overall rate of decline for the species may no longer approach the thresholds for listing as threatened and that the species may hence warrant listing as Least Concern.
However, there remains considerable uncertainty over the global trend due to significant data gaps throughout the range. While the European wintering population appears to be stable, the European breeding population trend is unknown due to a lack of data from Romania, where it is thought over 60% of this population breeds (BirdLife International 2015). On the basis of the information that was reported (excluding Romania) there appears to be a slight decline across all countries for which long-term trends could be calculated, which is slightly more pronounced when the negative short-term trend for the Croatia population (6% of the European breeding population) is included.
A literature review of West Siberian bird populations (van Impe 2013) indicated that 6 studies reported declines in the breeding population of Ferruginous Duck in Russia, from an estimated 12-14,000 pairs in the 1980s to between 500 and 1,500 pairs in 2003 (Ilyashenko 2011), but more recent trend information appears unavailable.
Trends in wintering populations elsewhere in Asia are also unclear. The Asian Waterbird Census 2008-2015 data demonstrates considerable variation due to the inconsistency in the number of sites surveyed. Over 10,000 individuals were recorded in 2008, 2011 and 2013, while fewer than 3,000 individuals were recorded in 2010 and 2015 (Mundkur et al. 2017). Bangladesh appears to be the key country for wintering for the eastern population, and while effort explains some of count variation between years, there appears to be a genuine multi-year cycle in numbers present in the country. Therefore, the best available data from Asia (which contains the largest flyway population in the world) does not provide any evidence for recent declines, just fluctuations.
The following tale presents the data shown in the Waterbird Population Estimates (Wetlands International 2017b) updated to include data from the AEWA Conservation Status Review 6 (Wetlands International 2017a), along with data from Mundkur et al. (2017).
|Population||Size (individuals)||% total||Trend||Reference(s)|
|West Mediterranean/North & West Africa||5,700 – 6,300||2.6 – 3.2||Unknown||see Wetlands International (2017a)|
|Eastern Europe/East Mediterranean & Sahelian Africa||50,000 – 82,000||27.7 – 34.4||Increasing||see Wetlands International (2017a)|
|Western Asia/South-west Asia & North-east Africa||25,000 – 50,000||13.8 – 21.0||Unknown||see Wetlands International (2017a)|
|Remaining Asian Distribution||100,000||42.0 – 55.3||Fluctuating||see Wetlands International (2017b); Mundkur et al. (2017)|
|Total||180,700 – 238,300|
Overall, and given the vast size of the range and the species’s apparent low site fidelity, the population trend is essentially uncertain. However, there does not appear to be any evidence suggesting that there is a rapid or moderately rapid decline that approaches 30% (i.e. 25-29%) in three generations (c. 23 years), and the rate of decline is presently estimated at 10-19% over three generations, which in itself is not sufficiently severe to be considered Near Threatened. Therefore, as the species does not presently approach the thresholds for listing as a Threatened species under any criteria, it is proposed that the species be downlisted to Least Concern.
If data from the breeding population in Russia and Romania are available and demonstrate recent negative trends sufficient to be causing a more severe rate of global decline, then maintaining the species as Near Threatened may be justified. Either way, such data would be very useful in supporting the species assessment.
BirdLife International. 2015. European Red List of Birds. Office for Official Publications of the European Communities, Luxembourg. http://datazone.birdlife.org/info/euroredlist
Ilyashenko, V. Y. 2011. Principles of compiling a catalogue of rare birds and the Red Data Book of the Russian Federation. Ornitologia 36: 157-187 (Russ.).
Mundkur, T., Langendoen, T. and Watkins, D. (eds.) 2017. The Asian Waterbird Census 2008-2015 – results of coordinated counts in Asia and Australasia. Wetlands International, Ede. http://www.eaaflyway.net/documents/resources/aewa%20ref/AWC_2008-2015_Summary_Report_31Mar17.pdf
van Impe, J. 2013. Esquisse de l’avifaune de la Sibérie occidentale: une revue bibliographique. Alauda 81(4): 269-296.
Wetlands International. 2017a. “Waterbird Population Estimates”. Retrieved from wpe.wetlands.org on Tuesday 23 May 2017. Updated from the AEWA Conservation Status Review 6.
Wetlands International. 2017b. “Waterbird Population Estimates”. Retrieved from wpe.wetlands.org on Tuesday 23 May 2017. Current data from http://wpe.wetlands.org/search?form%5Bspecies%5D=ferruginous+duck&form%5Bpopulation%5D=&form%5Bpublication%5D=5
Zhoa, Z. and MaMing, R. 2014. The status of Ferruginous Duck Aythya nyroca breeding and wintering in China. Wildfowl 64: 116-125.