The Arctic Loon – Master Diver of the North

The Arctic Loon – Master Diver of the North

Also known as the black-throated diver, the Arctic loon is a northern migratory waterbird of the Gaviidae family. Once considered conspecific with the closely related Pacific loon, these two birds are now regarded as sister species together with the yellow-billed and common loons.

Up Close and Specific

Loons resemble ducks in appearance and behaviour and they are similar sized. Unlike ducks with their marked sexual dimorphism, male and female loons are identical. From a distance, the Arctic loon’s shadowy plumage blends into the dark waters of the open ocean.

Closer inspection reveals a striking contrast of grey, black, and white. Bold stripes on the neck and breast of the breeding adult glint silvery around the characteristic black throat patch along with white spots with checkered markings on the back. These adornments are lost at the end of the breeding season, leaving non-breeding birds less decorated and eventually a drab brown with pale underparts, much like the juveniles. 

The Arctic loon is smaller and sleeker than its Pacific cousin, with which it bears a close resemblance and can be mistaken for where the ranges overlap in the region between Japan and Alaska. These two species even have a similar, harsh cackling call.

The Pacific loon has a shorter bill and a rounded head held parallel to the water surface, whereas the Arctic has a long, dagger-like bill and angular head tilted slightly upwards.

Arctic Loon

There are two recognised subspecies. The eastern race, G. a. Viridigularis, can be distinguished by the green of its throat patch.

Seasonal Movements and Habitat

Named for its breeding range across Arctic and Subarctic Eurasia, this seabird has a vast summer distribution extending from the British Isles across Arctic Russia and Siberia to Alaska’s Seward Peninsula. After the breeding season, they migrate south spending winters along the ice-free coasts of Europe and Asia. 

Winter populations can also be found along the northern seas, including the Baltic, Aegean, Black, Caspian, and North Seas. Rare sightings have been recorded south of Alaska in the United States, but many of these sightings have since been labelled as cases of mistaken identity with the Pacific loon.

The Arctic loon breeds in islets of the deep, isolated lakes in the taiga, tundra, and boreal forests. During winter, they take to sheltered coasts, bays, and inshore waters. 

Evolution and Adaptions

The genus Gavia is believed to have originated in Europe during the Paleogene, with fossils of the earliest species found the Czech Republic. 

Loons are exceptional divers and swimmers. Using their webbed feet to propel themselves, they are remarkably agile in the water—able to pivot and change direction within a second. 

Arctic Loon in Water

The Arctic loon is capable of reaching depths of up to 16 feet to find food and can hold its breath for up to 90 seconds underwater. A top predator of the pelagic and freshwater lakes alike, this species has a success rate of 80 percent. Sharp, backward-facing protrusions inside the upper mandible help them grip slippery prey. Like many other birds, loons swallow pebbles to aid in digestion.

Loons are atypical among avians in that they have solid bones, which makes them less buoyant. To conserve energy, they slow down their heartbeat underwater. They are also able to compress their feathers on command for a more streamlined shape, allowing them to move swiftly through the waters.

This skillfulness is not matched on land. Loons have difficulty walking as their feet are located too far back on the body to offer any stability on the ground. They can, however, run short distances when frightened.

Loons are strong fliers but require a fair amount of space to take off. They patter across the water upwind to create a runway. Once airborne, they are capable of flying long distances in a single stretch. The Arctic loon has a barking flight call.

Arctic Loon Floating

As migratory birds that move between freshwater and saltwater habitats, loons are well adapted to handle the changes in salinity. They have special glands above their eyes to filter out salts, flushing them through their nasal passages.

Behaviour and Ecology

Spring migrations begin in April, with northernmost populations waiting for the spring thaw. Arctic loons start building their nests in May—a process that takes roughly a week. Typical of seabirds, they nest on the ground. The oval-shaped nest is constructed by the female out of vegetation, leaves, and sticks. 

During the breeding season, males give a rhythmic whistling song. Courtship behaviour comprises a series of synchronised movements, such as bill dipping and splash diving, following which pairs mate on the lakeshore. Once the clutch—typically consisting of two eggs—is laid, both males and females share incubation and caring duties in the weeks after hatching.

Arctic Loon Close Up

As with many double-clutching species, it is normal for only one of the nestlings to survive, with the other often dying within a week. Surviving nestlings are vulnerable to predators and flooding. They fledge at around two months and reach sexual maturity in two to three years. Arctic loons return to the same nesting site year after year.

Did you know? Arctic loons are monogamous and mate for life. Pairs even stay together during migration and throughout winter.

The Arctic loon is largely piscivorous. It also preys on molluscs, crustaceans, and aquatic insects, as well as foraging for plant matter. 

Status and Conservation

Despite its extensive range, populations of the Arctic loon are declining. Major threats include habitat destruction, with acidification and pollution from heavy metals and oils near their fishing grounds being a significant cause. These birds are also impacted by fishing nets and coastal windfarms. They are currently classified as “least concern” by the International Union for Conservation of Nature (IUCN) but are protected by the Agreement on the Conservation of African-Eurasian Waterbirds and the Migratory Bird Treaty Act in North America.

Final Thoughts

Aquatic birds across the globe are facing unprecedented rates of habitat destruction. Loons are excellent indicator species. They require pristine lakes for fishing and foraging. As they are sensitive to pollutants, their presence or absence can provide information on water quality and environmental contamination.

Declining loon populations are, therefore, a testament to a degrading ecosystem. Efforts to protect vulnerable species would benefit all species dependent on the lakes, oceans, and seas of the north.

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