Surf scoters are a species of sea duck that spend the winter months in coastal waters and breed in the northern parts of North America and Eurasia. They get their name from their preference for surf zones and affinity for mussels, their main food source. Surf scoters have distinctive plumage – the males are solid black with colorful patches on their bills while females are brown. Their populations have declined in recent decades, leading some to wonder – are surf scoters rare?
Surf Scoter Population and Conservation Status
Surf scoters have a large range but their populations have been decreasing. According to the IUCN Red List, surf scoters are classified as Least Concern globally. However, some regional populations are recognized as threatened or endangered.
In North America, Partners in Flight estimates a global breeding population of 710,000 surf scoters. The Sea Duck Joint Venture gives a wintering population estimate of 550,000 on the Atlantic coast and 1,000,000 on the Pacific coast. Their numbers have declined by at least 50% since the 1950s. Surf scoters face threats from oil spills, habitat loss, disturbance, and entanglement in fishing gear.
On the U.S. Endangered Species List, the Steller’s eider is listed as Threatened but the other two subspecies – surf scoter and white-winged scoter – are not listed. They are protected under the Migratory Bird Treaty Act. In Canada, surf scoters are listed as a species of Special Concern.
So while surf scoters have declined significantly in North America, their large range and population size means they are not globally rare or endangered currently. However, conservation action may be needed to stabilize populations.
Breeding Range and Habitat
Surf scoters breed in subarctic and boreal forest lakes and ponds in Alaska, Canada, and northeastern Siberia. They prefer shallow freshwater lakes and ponds surrounded by coniferous or mixed forests and interspersed with wooded bogs.
Ideal breeding habitat has an abundance of small fish and aquatic invertebrates to feed developing young. Large wetland complexes and areas with many small ponds provide the best breeding habitat.
Wintering Range and Habitat
In the winter, surf scoters migrate down the Pacific and Atlantic coasts to temperate coastal waters. On the Pacific coast, they range from the Aleutian Islands down to Baja California. On the Atlantic, they are found as far south as North Carolina.
Surf scoters prefer coastal bays, estuaries, and rocky shorelines in the winter. They are commonly found in nearshore waters less than 25 meters deep. Prime winter habitat provides ample mussels and other prey items.
Surf Scoter Diet
Breeding Season
Surf scoters undergo a striking dietary shift between breeding and wintering seasons. On the breeding grounds, they feed predominantly on aquatic insects and larvae. Males have elaborate courtship displays, using their colorful bills to scoop up mouthfuls of insects to show off for potential mates.
Females build up energy reserves by consuming aquatic insects and larvae to prepare for egg production. Chironomid midges, caddisflies, mayflies, and aquatic beetles make up the majority of their diet.
Winter Diet
In coastal waters, surf scoters switch to feeding almost exclusively on mussels, clams, and some crustaceans. The bulk of their diet consists of blue mussels and soft-shell clams pried off rocks or dredged from the seafloor.
They are able to swallow mussels whole using their powerful esophagus muscles to crush the shells. This allows them to efficiently consume large quantities during winter to meet energy needs. Their unique bills are well-adapted for mussel feeding.
Feces Study Insights
Analysis of surf scoter feces provides great insight into their diet. Studies of fecal samples show mussels typically make up over 90% of their food intake in winter. The remaining portion contains sea stars, crabs, and fish remains.
Sex differences exist as well – female scoters tend to consume more clams and male scoters eat more mussels. So their winter diet composition can be deduced from their feces contents.
Surf Scoter Behavior and Life Cycle
Migration
Surf scoters are migratory sea ducks. They breed in northern latitudes and winter along temperate coasts. In spring, males depart first and females follow shortly after their eggs hatch. They molt and regrow their flight feathers before migrating south in the fall.
Surf scoters have high site fidelity, returning to the same wintering and breeding areas year after year. They form large flocks during winter and migrate in groups along established flyways along coastlines.
Breeding and Nesting
Breeding occurs from May to July across their northern range. Males return first to establish and defend breeding territories on ponds and lakes. After courtship, females build nests on the ground concealed in vegetation near water.
Nest success is variable but often low due to predation. Females lay around 5-9 eggs and incubate them for about a month before they hatch. The precocial young leave the nest shortly after hatching.
Brood-Rearing
Females attend to and protect the young broods on their own. Ducklings feed on available aquatic insects and larvae. Mothers may move broods overland to new wetlands as resources are depleted.
High protein requirements mean young scoters must forage almost constantly. Groups of females may combine broods on productive lakes. After fledging at around 6 weeks, mothers abandond their offspring and migrate south.
Wintering Behavior
On coastal wintering grounds, surf scoters form large mixed-sex flocks numbering in the thousands. They forage in shallow subtidal zones, diving to the bottom to feed on mussels.
Their courtship displays resume as pairs reestablish bonds. Males actively advertise for mates using elaborate posturing and vocalizations. Aggressive encounters occur as males compete foraccess to females.
Surf Scoter Population Threats
Several key threats have contributed to declining surf scoter populations:
Habitat Loss and Degradation
Destruction and modification of wetland breeding habitat reduces nesting areas and food availability. Draining small ponds for agriculture and development pressures have decreased breeding sites.
Pollution and eutrophication of winter coastal habitat degrades food supplies. Spills of oil and other contaminants can disrupt feeding and survival.
Disturbance and Hunting
Increased disturbance from recreational boating and other activities can displace flocks from prime feeding areas. Hunting further reduces their numbers, especially in eastern North America.
Overharvest of Mussels
Commercial mussel fisheries may deplete their main winter food source in some coastal areas, forcing scoters to switch to less profitable prey and expend more energy foraging.
Oil Spills and Chemical Pollution
Seabirds like scoters are vulnerable to oil spills which can poison them and destroy plumage insulation. Chemical pollution bioaccumulates in the food chain and impairs reproduction.
Conservation and Management Strategies
To protect declining scoter populations, wildlife managers have implemented a number of conservation strategies:
Habitat Protection and Restoration
Securing important wetland complexes for breeding and safeguarding crucial wintering areas. Restoring degraded habitat by reducing pollution and manipulating water levels.
Nest Site Management
Installing nest boxes and predator screens to improve nest success. Managing water levels around nests to prevent flooding.
Hunting Regulation
Restricting hunting season length and bag limits in eastern North America to limit overharvest.
Productivity Monitoring
Conducting nest counts, brood surveys, and banding studies to track population trends over time. Modeling populations to guide management.
Education and Outreach
Promoting stewardship of scoters and their habitats among decision makers and private landowners through environmental education.
Research Priorities for Surf Scoters
Key knowledge gaps remain in our understanding of scoter ecology. Priority research needs include:
Migration Patterns and Connectivity
Studying migration routes and linkages between breeding, migratory stopover, and wintering sites using satellite telemetry and stable isotope analysis.
Population Delineation
Understanding population structure and delineation between breeding areas and wintering grounds using genetics, banding, and tracking data.
Reproductive Ecology
Examining breeding propensity, nest site selection, clutch size, and duckling survival through nest monitoring and capture-mark-recapture data.
Winter Foraging Ecology
Investigating habitat use, prey selection, foraging energetics, competition, and food limitations to guide habitat management.
Subpopulation Trends
Monitoring various subpopulations long-term to identify differences in regional trends and target declining segments.
Filling these research gaps will improve conservation planning and help stabilize surf scoter populations.
Conclusions
In summary, while surf scoters have a large total population and range, declines in North America and threats to breeding and wintering habitat are causes for concern. Their specialized ecology makes them vulnerable to habitat loss, prey fluctuations, pollution, and disturbance.
Continued monitoring and protection of key sites along with advancement in research of their migration patterns, reproductive biology, and winter ecology will be critical for guiding effective conservation of surf scoters into the future. Sustained investment into habitat management and downlisting threats is needed to reverse population declines.
Though not currently globally rare, targeted conservation action is warranted to prevent further decreases and ensure the long-term viability of North America’s iconic sea ducks. With proper science-based habitat protection and management, surf scoter populations can be restored to healthy levels.