NT
Black Scoter Melanitta americana



Justification

Justification of Red List Category
This newly split species is listed as Near Threatened on the basis that it is suspected to be undergoing a moderately rapid population decline owing to a number of widespread threats.

Population justification
The total population is estimated to number c.530,000-830,000 individuals (Delany and Scott 2006), probably including c.350,000-560,000 mature individuals, on the basis that they account for around 2/3 of the population.

Trend justification
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 U.S. 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 (Sea Duck Joint Venture 2003). Estimates from a relatively new survey indicate that the breeding population in western Alaska is currently c.160,000 birds and appears to have increased slightly since the survey was initiated in 2004 (R. Stehn per T. Bowman in litt. 2012). Mid-winter inventory data do not indicate any trends on the Pacific coast and only show a weak 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 (CBC) data indicates an overall 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). This equated to a decline of c.50% over 40 years, and thus suggests a c.32% decline over the last three generations (23 years), under the assumption of an exponential trend. However, CBC data are probably unreliable for tracking trends in this species because it winters predominantly offshore, where a large proportion of birds may not be visible to shore-based observers. Trends are apparently uncertain 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 Delany and Scott 2006); thus more research is required. Limited data and anecdotal evidence from South Korea suggests that the species has declined substantially as a wintering species since the 1960s and 1970s (N. Moores in litt. 2012). On the basis of this mixed evidence, the population is suspected to be undergoing a moderately rapid decline (i.e. 20-29% over three generations).

Distribution and population

Melanitta americana breeds in western Alaska (USA), Newfoundland (Canada) and far-eastern Russia (e.g. Collinson et al. 2006). It winters at sea off north-east America, and in the Pacific on the coasts of North America south to northern Baja California, Mexico, Russia, Japan, Korea and eastern China (del Hoyo et al. 1992).

Ecology

Behaviour This species is strongly migratory (del Hoyo et al. 1992) and often travels considerable distances over land making brief stop-overs on inland waters (Madge and Burn 1988). It arrives on its breeding grounds between late-April and May and breeds from late-May onwards (Madge and Burn 1988) in highly dispersed (Kear 2005) solitary pairs (del Hoyo et al. 1992). After mating (from June onwards), males migrate long distances prior to their flightless moult, most travelling in small groups to inshore or offshore coastal waters (Madge and Burn 1988). Females and juveniles leave the breeding grounds in September (Madge and Burn 1988). The species is highly gregarious when not breeding (Madge and Burn 1988) with males forming large congregations during the flightless moulting period (Kear 2005). Large flocks of several hundred to a thousand (Snow and Perrins 1998) or occasionally over 100,000 individuals can be observed during winter (Scott and Rose 1996). Non-breeders often oversummer on the wintering grounds (Madge and Burn 1988). Habitat Breeding The species breeds on Arctic dwarf heath (Snow and Perrins 1998, Kear 2005) or boggy tundra on pools, small lakes, streams (del Hoyo et al. 1992) and slow-flowing rivers (Snow and Perrins 1998). It shows a preference for freshwater habitats (del Hoyo et al. 1992) with low banks (Flint et al. 1984), small islets (Kear 2005) and high abundances of aquatic invertebrate and plant life positioned in swampy valleys or among mossy bogs (Flint et al. 1984), especially where suitable shrubs (e.g. willow or birch) and herbaceous vegetation are available for nesting cover (Johnsgard 1978, Snow and Perrins 1998, Kear 2005). It generally avoids areas with steep slopes or wetlands enclosed by forest (Kear 2005). Non-breeding Although the species may use freshwater lakes on migration (Madge and Burn 1988, Kear 2005) the majority moult and overwinter at sea (Kear 2005) or shallow inshore waters less than 20 m deep (Kear 2005) (optimally 5-15 m [Scott and Rose 1996]) with abundant benthic fauna (Kear 2005), generally between 500 m and c.2 km from the shore (Snow and Perrins 1998). Diet Its diet consists predominantly of molluscs, especially during the winter (del Hoyo et al. 1992), although it occasionally takes other aquatic invertebrates such as crustaceans (del Hoyo et al. 1992) (e.g. barnacles and shrimps [Johnsgard 1978]), worms (del Hoyo et al. 1992), echinoderms, isopods, amphidods (Kear 2005) and insects (e.g. midges and caddisflies [del Hoyo et al. 1992]) as well as small fish (del Hoyo et al. 1992) and fish eggs (Snow and Perrins 1998). On the breeding grounds the species may also consume plant matter (del Hoyo et al. 1992) such as seeds, roots and tubers (del Hoyo et al. 1992) and the vegetative parts of aquatic plants (Flint et al. 1984). Breeding site The nest is a scrape on the ground hidden amongst vegetation (del Hoyo et al. 1992) close to water (Madge and Burn 1988, Kear 2005) or placed further away in dwarf heath (Kear 2005).

Threats

Through a variety of effects, climate change potentially represents the greatest threat to the species. Decreasing spring snow cover duration in North American boreal regions have been linked to population declines of Scoters, likely due to trophic mismatch (Drever et al. 2011), and future ocean acidification may lead to sustained declines in molluscs which form a large part of their diet (Steinacher et al. 2009, Carboneras and Kirwan 2017). The commercial exploitation of benthic shellfish poses an additional threat through competition for food resources (Kear 2005). Oil spills and chronic oil pollution threaten the species in the winter moulting period where large and highly vulnerable concentrations of the population occur, while oil drilling sites could also cause low-level impacts through human disturbance and degradation of food resources (Gorski et al. 1977, Nikolaeva et al. 2006). In parts of the range, avoidance of busy shipping areas by flocks of the species could displace flocks from preferred feeding areas. Hunting represents another threat to the species, with an average of 9,500 birds reported to be shot annually in the US and an additional 7,000 per year in Canada through the 1980s and 1990s. However, the actual number killed may have been much higher with maximum estimates exceeding 24,000 in the US in 1974 and 23,000 annually in Canada between 1974 and 1982 (Bordage and Savard 2011). Since this period, numbers of hunters have decreased considerably and the annual harvest has fallen concomitantly. The species is susceptible to avian influenza and may be threatened by future outbreaks of the virus (Melville and Shortridge 2006), however the disease is unlikely to affect the majority of the population at once and only small numbers of birds tested in various countries have developed the disease despite evident exposure to the virus. High-speed ferries can cause disturbance to this species (Larsen and Laubek 2005). In some areas, the breeding habitat is threatened by eutrophication from agricultural nutrient loads (Kear 2005).

Conservation actions

Conservation Actions Underway
No targeted conservation actions are known for this species, although it is monitored in parts of its range and occurs in some protected areas.

Conservation Actions Proposed
Improve monitoring surveys in order to obtain reliable baseline data and monitor future trends. Assess the significance of various threats. Tighten controls on marine pollution. Increase the area of suitable habitat that receives protection.

Acknowledgements

Text account compilers
Stuart, A., Taylor, J., Fjagesund, T., Butchart, S., Calvert, R., Hermes, C., Malpas, L., Ekstrom, J., Martin, R., Palmer-Newton, A.

Contributors
Pihl, S., Bowman, T., Moores, N.


Recommended citation
BirdLife International (2020) Species factsheet: Melanitta americana. Downloaded from http://www.birdlife.org on 23/10/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 23/10/2020.