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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.
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.
The specific name immer is derived from North Germanic names for the bird such as modern Icelandic "Himbrimi".
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".
Adults can range from 61 to 100 cm in length with a 122–152 cm wingspan. The weight can vary from 1.6 to 8 kg. On average, a Common Loon is about 81 cm long, has a wingspan of 136 cm, and weighs about 4.1 kg.
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 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 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.
Source: Parts of Wikipedia
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