Great northern diver
The Common loon (Gavia immer) is a large member of the loon, or diver, family of birds. These birds eat a variety of animal prey and swallow most of their prey underwater, where it is caught. Loons form strong pair bonds and their chicks are capable of diving underwater when just a few days old.
The adult breeding plumage of this bird consists of a broad black head and neck with a greenish, purplish, or bluish sheen. It has a black bill sometimes with a pale tip, and red eyes. The neck is encircled with a characteristic black ring and has two white necklaces of eight to ten short streaks on the upper foreneck, and a noticeable collar of white, parallel lines forming a large oval on the neck-side. The central lower foreneck is pure white, and the lower neck-sides has longitudinal white lines becoming rows of small spots and black lines becoming very narrow. The upperparts are blackish or blackish grey, and each feather has small white spots on it. The upperwing is blackish and with small white spots on the non-primary coverts, whereas the underwing is paler with white coverts except for the long black shaft streaks on the axillaries. The underparts are pure white but have some black on the undertail coverts and vent. It has a checkered black-and-white mantle and a blackish tail. The legs are pale grey on the inner half and blackish on the outer half, and the webs between the toes are flesh colored. Adult non-breeding plumage is brownish with a dark neck and head marked with dark grey-brown. The eyes are surrounded with white, and the eyelids are pale. The bill is mostly pale grey, with a dark culmen and tip, but in early spring the tip may turn whitish. The underparts, lower face, chin, and throat are also whitish. The foreneck is whitish, usually forming a wedge-shaped notch in dark neck sides, and may sometimes reveal a shadowy trace of the neck ring or a pale collar. It has dark brownish grey upperparts with an unclear pattern of squares on the shoulders and some wing coverts spotted with white, which are usually concealed while swimming. The male and the female have similar appearances, although they exhibit sexual dimorphism in their physical dimensions with the male larger and significantly heavier than the female. A juvenile often has a dark, brownish-grey nape that may look darker than the pale-edged black feathers. It has a dark grey to black head, neck, and upperparts, with white throat, cheeks, and underparts. During the first winter, the bill shape of the young may not be as fully developed as that of the adult, and during the second winter, it much resembles the breeding adult, but with wing coverts lacking white spots.
Common loons breed in the northern United States and Canada, as well as in southern parts of Greenland, Iceland, Svalbard, in Jan Mayen, and Bear Island in Norway; and in Alaska, to the west, and very rarely in Scotland, to the east. Some birds remain in Iceland year-round, although most migrate. In North America, they winter mainly along the North Atlantic and northeast Pacific coasts, many stopping off on the Great Lakes during their migration. In the east, Common loons winter along western European coasts. Their range extends into northwestern Europe from Finland to Portugal and southern and northwestern Spain (Galicia and Asturias), as well as the western Mediterranean off Catalonia, and off Morocco in Africa. During their breeding season in spring and summer, most Common loons live on lakes and tundra ponds. For protection from predators, they favor lakes with islands and coves. On the wintering grounds, these birds can be found along coasts and on inland lakes, bays, inlets, streams, and estuaries.
Common loons are generally solitary birds; they prefer to spend the day singly but may gather in flocks to sleep at night. These birds do all their hunting during the day. They are expert fishers, catching their prey underwater by diving as deep as 60 m (200 ft). Common loons have large webbed feet which make them efficient underwater pursuit predators and adroit divers. Loons use their powerful hind legs to propel their body underwater at high speed to catch their prey, which they then swallow head-first. If the fish attempts to evade, the bird chases it down with excellent underwater maneuverability due to its tremendously strong legs. Most prey is swallowed underwater, where it is caught, but some larger prey is first brought to the surface. Common loons communicate with each other using the tremolo, the yodel, the wail, and the hoot calls. The tremolo call or "laughing" call is often used to signal distress or alarm caused by territorial disputes or perceived threats. The yodel is a long call made only by the male. It is used in the establishment of territorial boundaries and in territorial confrontations. A wail is a long call that is often compared to a wolf's howl. This call is used between breeding pairs or an adult and its chick. It is a loud 'aaoo, weee-wea weee-wea weee-wea', or 'ooo-aaah-éééé'. The hoot is a short, soft call used between small family groups or flocks. Common loons hoot to let other families or flock members know where they are or when parents summon their chicks to feed.
Common loons are carnivores (piscivores) and most of their diet consists of fish. The young typically eat small minnows, and sometimes insects and fragments of green vegetation. When there is either a lack of fish or they are difficult to catch, Common loons will prey on crustaceans, crayfish, snails, leeches, insect larvae, mollusks, frogs, annelids, and occasionally aquatic plant matter such as pondweed, roots, moss, willow shoots, seeds, and algae.
Common loons are monogamous; they form pair bonds that may last for several years. During the courtship, the birds perform mutual bill-dipping and dives. Nesting typically begins in early May. Breeding pairs patrol their territories routinely, even at night, defending the territory both physically and vocally. The male usually selects the nest location and both sexes then construct the nest. The nest itself is about 56 cm (22 in) wide and is made out of dead marsh grasses and other plants, and formed into a mound along the vegetated coasts of lakes. After a week of construction in late spring, one parent climbs on top to mold the interior of the nest to the shape of its body. The female lays two olive-brown oval eggs with dark brown spots and both parents incubate them for about 28 days. Newly hatched chicks are dark chocolate brown in color and have a white belly. Within hours of hatching, the young begin to leave the nest with the parents, swimming close by and sometimes riding on one parent's back. The chicks are capable of making shallow dives from their first day but make deeper dives as they grow. Fledging takes 70 to 77 days. Both parents feed the chicks live prey from hatching to fledging. As they grow, chicks are able to catch their prey by themselves and can feed and fend for themselves after about 2 months. Young Common loons become reproductively mature and start breeding when they are around 2-3 years old.
Common loons are threatened by habitat loss, pollution, as well as lead poisoning from fishing sinkers, and mercury contamination from industrial waste. Egg shells may also contain metal contaminants, leading to low reproductive productivity. Common loons also suffer from hunting, predation, water-level fluctuations, or flooding. They abandon lakes that don't provide suitable nesting habitats due to shoreline development. These birds are also endangered by personal watercraft and powerboats that may drown newly born chicks, wash eggs away, or swamp nests.
According to the IUCN Red List, the total population size of Common loons is 612,000-640,000 individuals. In Europe, the breeding population consists of 700-1,300 pairs, which equates to 1,400-2,600 mature individuals. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.
