Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <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 trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The European population is estimated at 800-900 pairs, which equates to 1,600-1,800 mature individuals (BirdLife International 2015). However Europe represents <5% of the global range. Wetlands International (2018) estimate the population at 205,500-257,800 individuals, rounded here to 205,000-258,00 individuals.
This species has undergone a large and statistically significant increase over the last 40 years in North America (171% increase over 40 years, equating to a 28.3% increase per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007). The European population trend is unknown (BirdLife International 2015).
The major breeding range of this species is along the western coast of the U.S.A. from southern Alaska to northern California. Breeding colonies are also found in Labrador (Canada), south-west Greenland (to Denmark) and Iceland. Some populations (e.g. Iceland) are sedentary, whereas others undertake longer trips to winter along the Pacific coast of Alaska and Canada, and the north-eastern coast of North America (del Hoyo et al. 1992).
This species breeds on freshwater lakes, pools and rivers in open or wooded country. It can be seen nesting as high as 3,000 m in the Rocky Mountains (U.S.A.). The species uses relatively productive lakes and rivers in Iceland. It is a hole-nesting species using natural holes in lava fields and nest boxes erected on farmhouses at the edge of the breeding area (Tucker and Heath 1994). Laying is usually from mid-May although slightly earlier if using nest boxes. It lays 8 to 11 eggs (Carboneras and Kirwan 2018). It feeds mainly on benthic invertebrates (Tucker and Heath 1994). Summer foods include insects and their larvae and plant material, whereas winter diet consists mainly of molluscs and crustaceans (del Hoyo et al. 1992). The species is not truly migratory, with some populations mostly sedentary, e.g. Iceland, and others moving distances of >1,000 km (Carboneras and Kirwan 2018). In Iceland there appears to be a large sex imbalance (per Carboneras and Kirwan 2018), but the causes of this are uncertain
Hunting occurs on both coasts of North America and eggs are collected in Iceland, but harvest is subject to quotas set to minimise any population impact (Eadie et al. 2000, Carboneras and Kirwan 2018), hence the present level of hunting is thought to be sustainable for the Icelandic and US west coast populations, but could potentially have a larger impact on the much smaller population on the US east coast (Eadie et al. 2000). Agro-industry plantations have contributed to habitat restrictions due to the loss or degradation of old forest featuring dead trees and large trees with dead limbs, which make for suitable nest cavities. The decrease in available nesting sites may have caused increased chick mortality due to greater distances separating nest holes from water (Eadie et al. 2000, Environment Canada 2013). Oil spills may pose a serious risk both through direct mortality from oiling and longer-term effects of chronic contamination pollution. In particular, the species may be exposed to pollutants when aggregating in wintering grounds which overlap with industrialised seaways such as the Gulf of St. Lawrence, Vancouver, Kittimat and Alice Arm and Baie-Comeau (Eadie et al. 2000). The species is also at risk from contamination of food resources, in particular blue mussels, which is a preferred prey item (Eadie et al. 2000). In Europe, the species is mainly confined to a small area in northeastern Iceland, with 85-90% of the national population occurring at Lake Mývatn and the River Laxá. Such a locally concentrated distribution makes the European population vulnerable to stochastic events, and the 1989 crash in food resources led to a halving of the Icelandic populations (Kear 2005). The planned introduction of Atlantic salmon Salmo salar into the river systems and sediment dredging in Lake Mývatn (Einarsson and Magnúsdóttir 1993) could have negative effects on future food availability through altered trophic dynamics in the ecosystem (Kear 2005).
Conservation Actions Underway
Bern Convention Appendix II. CMS Appendix II. Listed as Endangered on Icelandic National Red List (Institute of Natural History 2000). The species is fully protected from hunting in Iceland (Carboneras and Kirwan 2018).
Conservation Actions Proposed
Research should be undertaken into the species's ecology, habitat and foraging needs. An assessment of the impacts of S. salar introduction and sediment dredging should be made as well as ensuring the sustainability of local egg harvesting. Research studies into the causes of the population sexual imbalance should be developed.
Text account compilers
Ekstrom, J., Fjagesund, T., Ashpole, J, Butchart, S., Hermes, C., Calvert, R., Martin, R., Stuart, A.
BirdLife International (2019) Species factsheet: Bucephala islandica. Downloaded from http://www.birdlife.org on 17/02/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 17/02/2019.