|Adult in breeding plumage in Wisconsin, United States|
|Distribution of G. immer.
Not shown is the eastern part of the wintering range, which encompasses lakes and coastal areas down to Central Europe.
Breeding range Year-round range Wintering range
The common loon (Gavia immer) is a large member of the loon, or diver, family of birds. The species is known as the great northern diver in Eurasia; another former name, great northern loon, was a compromise proposed by the International Ornithological Committee.
The common loon is one of the five loon species that make up the genus Gavia, the only genus of the family Gavidae and order Gaviiformes. Its closest relative is the other large black-headed species, the yellow-billed loon or white-billed diver, Gavia adamsii.
The genus name Gavia was the Latin term for the smew (Mergellus albellus). This small sea-duck is quite unrelated to loons and just happens to be another black-and-white seabird which swims and dives for fish. It is unlikely that the Ancient Romans had much knowledge of loons, as they are limited to more northern latitudes and since the end of the last glacial period seem to have occurred only as rare winter migrants in the Mediterranean region. The specific name immer is derived from North Germanic names for the bird such as modern Icelandic "Himbrimi". The term may be related to Swedish immer and emmer, the grey or blackened ashes of a fire, referring to its dark plumage; or to Latin immergo, to immerse, and immersus, submerged. The European name "diver" comes from the bird's habit of catching fish by swimming calmly along the surface and then abruptly plunging into the water. The North American name "loon" may be a reference to the bird's clumsiness on land, and derived from Scandinavian words for lame, such as Icelandic "lúinn" and Swedish "lam". Another possible derivation is from the Norwegian word lom for these birds, which comes from Old Norse lómr, possibly cognate with English "lament", referring to the characteristic plaintive sound of the loon. The scientific name Gavia refers to seabirds in general.
Adults can range from 61 to 100 cm (24 to 39 in) in length with a 122–152 cm (48–60 in) wingspan, slightly smaller than the similar yellow-billed loon (or "white-billed diver"). The weight can vary from 1.6 to 8 kg (3.5 to 17.6 lb). On average, a common loon is about 81 cm (32 in) long, has a wingspan of 136 cm (54 in), and weighs about 4.1 kg (9.0 lb).
Breeding adults have a black head, white underparts, and a checkered black-and-white mantle. Non-breeding plumage is brownish, with the chin and foreneck white. The bill is black-blue and held horizontally. The bill colour and angle distinguish this species from the similar yellow-billed loon.
Bone structure: A number of solid bones (unlike normally hollow avian bones), which add weight but help in diving.
Distribution and habitat
In the spring and summer, most common loons live on lakes and other waterways in Canada and the northern United States.  The summer habitat of Common Loons ranges from wooded lakes to tundra ponds. The lakes must be large enough for take-off and provide a high population of small fish. Clear water is necessary so that they can see fish to prey on. As protection from predators, loons favor lakes with islands and coves.
Loons during their winter migration can be seen as far as Baja California and Texas in the south and northwestern Europe in the east. Loons usually migrate to the nearest body of water that will not freeze over in the winter: western Canadian loons to the Pacific, Great Lakes loons to the Gulf of Mexico region, eastern Canadian loons to the Atlantic, and some loons to large inland lakes and reservoirs.
This species, like all divers, is a specialist fish-eater, catching its prey underwater, diving as deep as 60 m (200 ft) and can remain underwater for as long as 3 minutes. Having large webbed feet, the loons are efficient predators, powerful swimmers, and adroit divers. Freshwater diets consist of pike, perch, sunfish, trout, and bass; salt-water diets consist of rock fish, flounder, sea trout, and herring. The bird needs a long distance to gain momentum for take-off, and is ungainly on landing. Its clumsiness on land is due to the legs being positioned at the rear of the body; this is ideal for diving but not well-suited for walking. When the birds land on water, they skim along on their bellies to slow down, rather than on their feet, as these are set too far back. The loon swims gracefully on the surface, dives as well as any flying bird, and flies competently for hundreds of kilometres in migration. It flies with its neck outstretched, usually calling a particular tremolo that can be used to identify a flying loon. Its flying speed is as much as 120 km/h (75 mph) during migration. Its call has been alternately called "haunting," "beautiful," "thrilling," "mystical," and "enchanting."
Common loon nests are usually placed on islands, where ground-based predators cannot normally access them. However, eggs and nestlings have been taken by gulls, corvids, raccoons, skunks, minks, foxes, snapping turtles, and large fish. Adults are not regularly preyed upon, but have been taken by sea otters (when wintering) and bald eagles. Ospreys have been observed harassing divers, more likely out of kleptoparasitism than predation. When approached by a predator of either its nest or itself, divers sometimes attack the predator by rushing at it and attempting to impale it through the abdomen or the back of the head or neck.
Common loons mate monogamously and annually. They begin breeding at two years of age. Copulation takes place ashore, often on the nest site, repeated daily until the eggs are laid. The preceding courtship is very simple, mutual bill-dipping and dives. The pair of mates claims a breeding territory of 60 to 200 acres and patrols it frequently, defending and marking the territory both physically and vocally. The displays toward strangers, bow-jumping, rushes etc. are often misinterpreted as courtship. Both the male and female parents build the nest and take turns incubating the eggs. If food is scarce, the young may fight intensely, and often only one young survives. The nests are constructed out of dead marsh grasses and other indigenous plants and formed into mounds along the vegetated coasts of lakes. After a week of construction in late spring, one parent climbs on top to mold the nest to the shape of its body. These nest sites are often reused annually, and studies suggest that these renesting attempts are more likely to succeed than the initial attempt.
Nest sites typically resemble those on which the parents were hatched. Instead of avoiding acidity and poor water quality, the parents risk reproductive success for better survival chances and choose lakes that yield similar fish to their regular diet.
The eggs hatch in just under a month. When the chicks are a few days old, they will begin to leave the nest with the parents, swimming and sometimes riding on one parent’s back. They are capable of diving underwater in the next few days and can typically fly at 10–11 weeks old.
Common loons have faced a decline in breeding range primarily due to hunting, predation, human destruction of habitat, contaminant exposure, and water-level fluctuations, or flooding. Some environmentalists attempt to increase nesting success by mitigating the effects of some of these threats, namely terrestrial predation and water-level fluctuations, through the deployment of rafts, artificial nesting islands, in the breeding territories of common loons.
Loons produce a variety of vocalizations, the most common of which are categorized into four main types: the tremolo, the yodel, the wail, and the hoot. Each of these calls communicates a distinct message.
The frequency at which loons vocalize has been shown to vary based on time of day, weather, and season. They are most vocally active between mid-May and mid-June. The wail, yodel, and tremolo calls are sounded more frequently at night than during the day, and calls have also been shown to occur more frequently in cold temperatures and when there is little to no rain.
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The tremolo call—sometimes called the “laughing” call—is characterized by its short, wavering quality. Loons often use this call to signal distress or alarm caused by territorial disputes or perceived threats. Loons also use the tremolo to communicate their presence to other loons when they arrive at a lake, often when they are flying overhead. It is the only vocalization used in flight.
The tremolo call has varying levels of intensity and can be identified as type I, II, or III. These levels correlate with a loon’s level of distress, and the types are differentiated by increasingly higher pitch frequencies added to the call.
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The yodel is a long and complex call made only by male loons. It is used in the establishment of territorial boundaries and in territorial confrontations, and the length of the call corresponds with the loon's level of aggression. Every male loon has a unique yodel, which changes if the loon changes territory.
A loon’s wail is a long call consisting of up to three notes, and is often compared to a wolf’s howl. Loons use this call to communicate their location to other loons. The call is given back and forth between breeding pairs or an adult and their chick, either to maintain contact or in an attempt to move closer together after being separated.
The hoot is a short, soft call and is another form of contact call. It is a more intimate call than the wail and is used exclusively between small family groups or flocks. Loons hoot to let other family or flock members know where they are. This call is often heard when adult loons are summoning their chicks to feed.
The diet of common loons consists primarily of fish, especially perch and sunfish in lakes and Atlantic croaker and Gulf silversides on ocean coasts. Common loons will feed on fish up to 10 inches in length, including minnows, suckers, gizzard shad, rock cod, and killifish. Young loons typically eat small minnows, and sometimes insects.
Common loons use their powerful hind legs to propel their bodies underwater at incredible speeds to catch their prey, which they then swallow headfirst. If the fish attempt to evade the grasp of the common loon, the bird will chase it down with excellent underwater maneuverability due to their tremendously strong legs. Most prey is swallowed underwater, where it is caught, but some larger prey is first brought to the surface.
Loons are visual predators, so it is essential to hunting success that the water is transparent. If there is either a lack of fish or of ability to catch fish, loons will prey on crustaceans, snails, leeches, insect larvae, mollusks, frogs, and occasionally aquatic plant life.
Relationship with humans
These birds have disappeared from some lakes in eastern North America due to the effects of acid rain and pollution, as well as lead poisoning from fishing sinkers and mercury contamination from industrial waste. Artificial floating nesting platforms have been provided for loons in some lakes to reduce the impact of changing water levels due to dams and other human activities.
In popular culture
This bird is well known in Canada, appearing on the one-dollar "loonie" coin and the previous series of $20 bills, and is the provincial bird of Ontario. Also, it is the state bird of Minnesota and appears on the Minnesota State Quarter.
The voice and appearance of the common loon has made it prominent in several Native American tales. These include a story of a loon which created the world in a Chippewa story; a Micmac saga describes Kwee-moo, the loon who was a special messenger of Glooscap (Glu-skap), the tribal hero; native tribes of British Columbia believed that an excess of calls from this bird predicted rain, and even brought it; and the tale of the loon's necklace was handed down in many versions among Pacific Coast peoples. Folk names include big loon, black-billed loon, call-up-a-storm, ember-goose, greenhead, guinea duck, imber diver, ring-necked loon, and walloon.
This bird is central to the plot of the children's novel Great Northern? by Arthur Ransome (in which it is referred to throughout as great northern diver, with the obsolete scientific name Colymbus immer). The story is set in the Outer Hebrides, where the main characters—a group of children on holiday—notice a pair of divers apparently nesting there. Checking their bird book, they believe this to be the great northern diver; however, this has not previously been seen to nest in northern Scotland, and so they ask for help from an ornithologist. He confirms that these birds are indeed the great northern; unfortunately, it soon transpires that he does not wish merely to observe, but wants to steal the eggs and add them to his collection; and to do this, he must first kill the birds. Published in 1947, the story is one where the conservationists are the eventual victors over the egg collector, at a time when the latter hobby was not widely considered to be harmful.
In the 2016 Pixar movie Finding Dory, a somewhat bedraggled and dimwitted loon named Becky is persuaded to use a bucket to help two of the main characters, clownfish Nemo and Marlin, get into a marine life institute where the titular Dory is trapped.
Loons were featured prominently in the 1981 film On Golden Pond.
Breeding adult swimming on Gull Lake, Ontario, Canada
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|Wikimedia Commons has media related to the common loon.|
|Wikispecies has information related to: Gavia immer|
- Common Loon stamps - bird-stamps.org
- Common loon (Gavia immer) - ARKive
- "Great Northern Diver (Gavia immer) media". Internet Bird Collection.
- DigiMorph.org — CT scans of a common loon skull
- Gavia immer - Animal Diversity Web
- Common loon Gavia immer - USGS Patuxent Bird Identification InfoCenter
- Loon Dreaming - animated short by the National Film Board of Canada
- Common loon photo gallery at VIREO (Drexel University)