Both the common loon (Gavia immer) and the Arctic loon (Gavia arctica) are large diving birds found in North America. They belong to the genus Gavia, which contains 5 species of loons worldwide. Loons are migratory birds that breed on freshwater lakes and ponds in the summer, and migrate to coastal waters for the winter.
The common loon and Arctic loon look very similar, and can be difficult to tell apart. However, there are some key differences in their size, coloration, breeding habitat, migration patterns, and vocalizations that birders can use to distinguish these two species. Learning how to identify loons takes practice, since the differences are often subtle.
Identification
Size
The most noticeable difference between these loons is their size. The common loon is larger and bulkier than the Arctic loon.
Species | Length | Wingspan | Weight |
---|---|---|---|
Common Loon | 31-43 in | 48-60 in | 7.7-18 lb |
Arctic Loon | 25-33 in | 42-52 in | 4-8 lb |
As the table shows, the common loon is noticeably bigger than the Arctic loon in all dimensions. This size difference is often apparent when seeing the two species together on the water. The common loon has a thicker neck and larger head compared to the Arctic loon’s more slender profile.
Coloration
Adult common loons and Arctic loons both have the characteristic black and white checkerboard plumage on their backs in summer. However, the common loon’s checks tend to be larger and bolder. The common loon’s head and neck feathers are darker black.
Arctic loons have more delicate facial patterns, with fine black and white lines along the neck. Their bills are also thinner and more needle-like than the common loon’s thicker bill.
In winter plumage, both species appear gray above and white below. The common loon has a darker gray saddle and hindneck. The Arctic loon is paler overall in winter. Its throat and foreneck are whiter.
Juvenile plumages are also slightly different, with fuzzy streaks on the Arctic loon young compared to the common loon’s scalier appearance. Leg color differs too – young common loons have greenish legs while Arctic loons are pinkish or flesh-colored.
Breeding Habitat
Common and Arctic loons use different breeding habitats in summer. Common loons favor large lakes and ponds, including reservoirs and slow rivers. They need a minimum of 4 hectares of open water for breeding.
Arctic loons breeding further north tend to use small ponds under 4 hectares, including shallow tundra pools. They will also use swift moving streams and rivers. Arctic loons are more adaptable to small water bodies since they make smaller nests.
The common loon is territorial and less tolerant of other loon pairs when nesting. Each pair needs at least 20-30 hectares of lake habitat. Arctic loons nest more densely, with 2-3 pairs per small tundra pond in optimal habitat.
Migration
The migration patterns of common and Arctic loons also differ. Common loons migrate primarily across land to reach their coastal wintering areas along the Atlantic and Pacific coasts. They take more inland routes through the Great Lakes region.
Arctic loons migrate earlier in fall across the ocean, from their arctic breeding sites to the Atlantic and Pacific coasts. They take more offshore routes to their wintering habitats. In spring, Arctic loons return to the arctic later than common loons.
Vocalizations
The calls of common and Arctic loons are one of the best ways to identify them in the field. The common loon’s iconic yodeling call is lower-pitched and more drawn out. It carries over greater distances across lakes.
Arctic loons make higher-pitched yodeling calls that sound thinner. Their calls are also faster-paced and quicker than the common loon. Both species use various yodeling calls between mates and territorial calls. Getting to know their distinct vocal styles takes practice.
In summary, the common loon is a bulkier bird that breeds on larger lakes, takes inland migration routes, and has a slower, crooning call. The Arctic loon is smaller and slimmer, favors small tundra ponds, migrates offshore, and has a quicker, higher-pitched call. Paying attention to these differences will help birders distinguish these two northern loons.
Range and Distribution
The breeding and wintering ranges of common loons and Arctic loons differ across North America due to their habitat preferences and migration patterns.
Common Loon
Common loons breed across Canada and the northern United States, including:
- Alaska
- Northern Canada
- Pacific Northwest
- Western Montana
- Great Lakes region
- Northeastern U.S.
- Maritime Provinces of Canada
- Newfoundland
They winter along both coasts from the U.S. to Mexico, and inland on the Great Lakes. The highest densities are along the Mid-Atlantic coast.
Arctic Loon
Arctic loons have a more northerly distribution. They breed in arctic and subarctic regions of:
- Alaska
- Northern Canada
- Nunavut
- Greenland
- Iceland
Small numbers breed in northern Montana, the Pacific Northwest, and northeastern Canada. In winter, they are found along both the Pacific and Atlantic coasts, ranging from Alaska to Baja California and Newfoundland to Florida.
The breeding ranges overlap in northern Canada and Alaska. Further south, only the common loon breeds across the northern tier of U.S. states and south-central Canada. Arctic loons are rare and local breeders in the continental U.S. In winter, both species occupy the coasts, but the Arctic loon favors more northern areas such as Washington and Massachusetts, while the common loon is more abundant further south.
Population and Conservation
Both common and Arctic loons have experienced population declines in parts of their range, primarily due to habitat loss and degradation. However, their global population statuses differ.
Common Loon
There are approximately 3 million adult common loons globally. Their population trends vary regionally:
- Increasing in interior Alaska and Canada
- Stable or increasing in eastern Canada
- Potential declines in western Canada
- Declining in northeastern U.S.
The common loon is protected under the Migratory Bird Treaty Act in the U.S. and Canada. It is currently listed as a species of Least Concern globally by the IUCN. However, some regional populations are listed as Endangered, Threatened, or Species of Special Concern.
Major threats include:
- Lake shore development
- Lead poisoning from fishing gear
- Disturbance of nesting sites
- Mercury contamination
- Oil spills in marine habitats
Arctic Loon
The Arctic loon has a global population estimated at 1.3-1.7 million adults. Population trends are mostly unknown, but are suspected to be declining in portions of its range. Threats to Arctic loons include:
- Oil spills
- Alaskan and Canadian mine drainage
- Mercury contamination in arctic ecosystem
- Coastal wind farms in migration route
- Subsistence harvest by indigenous communities
The Arctic loon is protected under the Migratory Bird Treaty Act. Its global population is currently stable enough to merit a conservation status of Least Concern. However, more surveys are needed to better understand local population trends for this northern species.
Behavior
Common and Arctic loons exhibit similar behaviors in many respects, but some key differences exist:
Diet
Both species feed mainly on fish, which they catch by diving underwater. Common loons take larger fish, including perch, pike, bass, and trout. Arctic loons eat smaller fish like minnows, sticklebacks, and young trout.
Their choice of fish prey depends on what habitats they are in. In coastal wintering areas, they feed on bottom-dwelling fish like sculpins, rockfish, and sand lance.
Diving
These loons are excellent divers, using their strong legs to propel them underwater where they pursue fish. On average, common loons can dive deeper – up to 60 meters – compared to the Arctic loon’s 20-30 meter diving range. However, Arctic loons are thought to be more efficient underwater hunters.
Both species use their sharp bills to grasp fish tightly, swallowing small fish underwater before surfacing. They employ a wide range of diving techniques to hunt different fish prey in various lake and ocean conditions.
Nesting
Common and Arctic loons build very simple nests during breeding season, scraping out a shallow depression on shore or an island. Common loons favor larger islands or muskrat houses for nest sites protected from mainland predators.
Arctic loons often nest right on shorelines or peninsulas, since their smaller tundra ponds lack islands. Their nests are more vulnerable to foxes, mink, gulls, and jaegers. Adults are highly territorial and defensive during nesting.
Nesting common loons produce a clutch of 1-3 speckled olive or brown eggs. Arctic loons lay just 2 eggs per clutch, in a lighter olive or green color. Incubation lasts 24-29 days, with both parents sharing duties.
Migration
Both loons migrate as solitary birds, traveling separately from their breeding pairs. They migrate at night and use coastlines, lake systems, or major rivers as navigational aids.
Young loons generally return north 2-3 years after hatching to find mates and potential territories. Loons exhibit high mate and breeding site fidelity once established.
Socialization
Common and Arctic loons lead mostly solitary lives outside the breeding season. They are territorial and intolerant of conspecifics (others of their species) during nesting and rearing young.
In migration and winter, they may loosely congregate in loose flocks off coastlines, but do not coordinate activities. Their communication consists mainly of territorial yodeling and contact calls between mates. They are aggressive in confrontations with other loons.
Overall, common and Arctic loons share general traits and adaptations as diving bird species. But their differing sizes, habitats, geographic ranges, and migration patterns account for subtle variations in their behavior, biology, and conservation status across North America.
Conclusion
In summary, the common loon and the Arctic loon are very closely related bird species within the genus Gavia, but demonstrate key differences in:
- Size and proportions – Common loons are larger and bulkier
- Plumage – Subtle variations in facial patterns and bill shape
- Breeding habitat – Common loons use larger lakes, Arctic loons use small tundra ponds
- Range – Arctic loons breed further north; more overlap in winter
- Migration routes – Commons loons more inland, Arctic more coastal
- Vocalizations – Arctic yodel higher pitched
- Diving abilities – Common loon dives deeper; Arctic loon more efficient
- Fish prey – Common takes larger fish
- Population status – Common more abundant globally
Being able to distinguish these similar-looking northerly diving birds takes practice. Focus on size differences, vocalizations, habitat, and subtleties of plumage patterns in the field. Both species are vulnerable to habitat loss and degradation, particularly from lakeshore development and pollution. continued monitoring and protection of loon populations will be important for these iconic North American waterbirds. Careful identification and reporting contributes to better understanding their conservation status across their breeding and wintering ranges.