LC
Barrow's Goldeneye Bucephala islandica



Justification

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 stable, 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.

Population justification
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. Latest wintering surveys in 2017 recorded 7,700 individuals in the eastern Canadian population (with 80% of this population found on the St. Lawrence Estuary and Gulf), with a further 500 individuals wintering in the Maritime provinces and 100 individuals in Maine (Canadian Wildlife Service Waterfowl Committee 2020). The western Canadian population has recently been estimated at 260,000 individuals, with 18,300 individuals present in the Central Interior Plateau Region (observed in 2019; Canadian Wildlife Service Waterfowl Committee 2020). The recent Partners in Flight (2019) reassessment estimates the North American population size to be 180,000 mature individuals. The Alaskan population is unknown, as surveys will usually combine Barrow's and Common Goldeneyes Bucephala clangula when counting (J-P. Savard in litt. 2020). The overall population is therefore tentatively placed in the band 175,000-200,000 mature individuals, roughly equating to 260,000-300,000 individuals, though this number requires confirmation.

Trend justification
This species was shown to have 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 Partners in Flight (PiF 2019) reassessment of North American birds however showed that between 1970 and 2014, the population trend was uncertain or slowly decreasing. Similarly, the recent North American Breeding Bird Survey recorded a 56% decline between 1966 and 2015, assuming a constant rate of decline (Sauer et al. 2017). Historical records also show that the population was thought to be declining by an estimated 1.26% yearly between 2000 and 2015 (Sauer et al. 2017). However, these decline rates are non-significant, with a large uncertainty in the overall population trend. Similarly, the British Columbia Coastal Waterbird Survey showed that the population had declined across the Strait of Georgia at a rate of 4.3% a year from 1999-2011 (Crewe et al. 2012), translating to over 50% decline within a 3-generation period (19.5 years; Bird et al. 2020). However, declines across the Salish Sea are not as significant (Crewe et al. 2012, G. Sorenson in litt. 2020, Ethier et al. in prep). The western Canadian population has additionally seen stability over the past two decades, with the eastern population thought to have increased by 30% between 2014 and 2017 wintering surveys (Canadian Wildlife Service Waterfowl Committee 2020). The Icelandic population generally fluctuates as the species moves throughout suitable habitat ranges, with an increase recorded between 2008-2011 in Mývatn and Laxár, a decline from 2011 to 2012, and then higher numbers seen in 2018 (Kolbeinsson et al. 2019). The European population trend is unknown (BirdLife International 2015). Thus, based on available information, localised declines and fluctuations (which are largely statistically non-significant), as well as unreliability in survey methods are thought to be unrepresentative of the overall population. The population is therefore considered to be stable throughout most of its range (Eadie et al. 2020).

Distribution and population

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. The population in Greenland is likely now extirpated (Eadie et al. 2020). Some populations (e.g. Iceland) are sedentary (primary breeding taking place in the Mývatn area; Pearce et al. 2014), 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). Thus, it is thought to exist in four distinct populations (Iceland, North America, Alaska, and the Pacific Coast (Pearce et al. 2014, J-P. Savard in litt. 2020). Interchange between the eastern and western North American populations is thought to be very rare, and potentially nonexistent (Pearce et al. 2014). The Canadian population is geographically divided into the smaller eastern and larger western populations (Canadian Wildlife Service Waterfowl Committee 2020).

Ecology

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 6 to 12 eggs (Eadie et al. 2020). It feeds mainly on benthic invertebrates (Tucker and Heath 1994). Wintering usually takes place on marine habitats (such as bays, harbors, fjords, inlets with rocky shores or mussel beds, creeks, waterfalls, or even storm drains; Eadie et al. 2020). 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 (Eadie et al. 2020).

Threats

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, 2020), 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). Similarly in Canada, annual harvests across five eastern provinces (Atlantic Canada and Quebec) have shown that less than 1,000 individuals are shot per year, with less than 5,000 birds shot by the Pacific Flyway sport harvest (from Alaska, British Columbia, and Washington State), and 3,000 birds harvested in Alaska; hunting pressure is thus considered relatively low (Canadian Wildlife Service Waterfowl Committee 2020). 

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). The Mountain Pine Beetle (Dendroctonus ponderosae) infestation and forest fires have additionally destroyed many mature forests in the Central British Columbia area (Canadian Wildlife Service Waterfowl Committee 2020). Recreational sport fishing, boats, and altering aquatic habitats may also reduce food availability and conflict between neighboring bird territories as the species attempts to flee disturbance (Canadian Wildlife Service Waterfowl Committee 2020).

Conservation actions

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 (Eadie et al. 2020). The eastern population in Canada was listed as a species of Special Concern in 2003, under the Species at Risk Act (Canadian Wildlife Service Waterfowl Committee 2020). The daily bag limit was subsequently restricted to one bird per day. 

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. Establish safe next boxes in areas where nesting trees are reduced, a common method used for monitoring Common Goldeneyes in Scotland and Maine (Eadie et al. 2020).

Acknowledgements

Text account compilers
Fernando, E.

Contributors
Einarsson, A., Fjagesund, T., Hermes, C., Lepage, C., Robert, M., Savard, J., Sorenson, G., Stuart, A. & Young, G.


Recommended citation
BirdLife International (2022) Species factsheet: Bucephala islandica. Downloaded from http://www.birdlife.org on 18/08/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 18/08/2022.