Birds
Common Loon
Gavia immer · also called common loon, great northern diver
The common loon is the voice of the northern wilderness — a heavy, dagger-billed diving bird whose wailing and yodelling calls carry across still lakes at dusk. It is built so completely for underwater hunting that it has almost given up on land, and nearly given up on easy flight.
Overview
Common loons breed on clear, fish-rich forest lakes across Canada, Alaska, the northern US, Greenland, and Iceland, and winter on coastal seas and large lakes further south, reaching western Europe (where it is called the great northern diver). In breeding plumage it is boldly checkered black and white with a green-black head and red eyes; in winter it is plain grey.
Built to dive
The loon is a diving specialist:
- Partly solid bones reduce buoyancy — unusual for a bird
- Legs set at the very back of the body for propulsion
- A streamlined shape and the ability to squeeze air from its feathers
It can dive to 60 metres and stay under for up to 90 seconds, chasing fish by sight.
The cost on land and in the air
Those same adaptations make the loon helpless on land — it cannot walk, only shuffle on its breast — so it nests right at the water’s edge. And its small wings mean it must run across the water for 30–400 metres to take off. A loon that lands on a wet road or a pond that is too small can be permanently stranded.
The calls
Loons have four calls: the mournful wail (contact), the laughing tremolo (alarm, and the only call given in flight), the male-only yodel (territorial, and unique to each bird), and a soft close-range hoot.
Status
The common loon is Least Concern and generally stable, but it is declining at the southern edge of its range and is vulnerable to lake acidification, shoreline development, boat strikes, and above all lead poisoning from swallowed fishing sinkers, which several regions have now restricted.
Common Loon: common questions
Why can't a loon walk on land?
A loon's legs are attached very far back on its body, almost at the tail. This placement makes them superb paddles — the legs act like a boat's propeller right at the stern — and combined with the loon's dense bones and streamlined shape it makes an outstanding diver. But it means the legs cannot support the bird's weight underneath it, so a loon cannot stand or walk. On land it can only push itself forward on its breast in an awkward shuffle, which is why loons come ashore only to nest, and always right at the water's edge.
What do the loon's calls mean?
Common loons have four main vocalisations. The wail is a long, mournful, rising note used to keep in contact with a mate or chick across a lake or in fog. The tremolo is a wavering, laughing call given when a loon is alarmed or defending territory, and it is the only call a loon gives in flight. The yodel is a longer, escalating call made only by males, and each male's yodel is individually distinctive — if he moves to a new territory, he changes his yodel. The fourth, the hoot, is a short, soft call used at close range between family members.
Why does a loon need such a long stretch of water to take off?
The same dense bones and rear-set legs that make a loon a great diver make it a poor flyer at low speed. Its wings are relatively small for its weight, so it cannot simply jump into the air. Instead it has to run across the surface of the water, flapping hard, for anywhere from 30 metres on a windy day to 400 metres in calm conditions, before it reaches flying speed. This is why loons only nest on lakes with enough open water, and why one that mistakes a rain-slicked parking lot or a small pond for a lake can become trapped, unable to get airborne again.
How does lead fishing tackle harm loons?
Loons swallow small stones from the lakebed to help grind food in their gizzard, and they sometimes pick up lost lead sinkers and jig heads, or eat a fish that is trailing lost tackle. A single small lead sinker in the gizzard is enough to poison and kill an adult loon within a few weeks. Lead poisoning from fishing tackle is one of the leading causes of death in adult common loons in parts of their range, which has led several US states and Canadian provinces to restrict the sale or use of small lead sinkers.