Common Loon

## Description

The common loon or great northern diver (Gavia immer ) is a large member of the loon, or diver, family of birds. Breeding adults have a plumage that includes a broad black head and neck with a greenish, purplish, or bluish sheen, blackish or blackish-grey upperparts, and pure white underparts except some black on the undertail coverts and vent. Non-breeding adults are brownish with a dark neck and head marked with dark grey-brown. Their upperparts are dark brownish-grey with an unclear pattern of squares on the shoulders, and the underparts, lower face, chin, and throat are whitish. The sexes look alike, though males are significantly heavier than females. During the breeding season, loons live on lakes and other waterways in Canada; the northern United States (including Alaska); and southern parts of Greenland and Iceland. Small numbers breed on Svalbard and sporadically elsewhere in Arctic Eurasia. Common loons winter on both coasts of the US as far south as Mexico, and on the Atlantic coast of Europe.

Common loons eat a variety of animal prey including fish, crustaceans, insect larvae, molluscs, and occasionally aquatic plant life. They swallow most of their prey underwater, where it is caught, but some larger items are first brought to the surface. Loons are monogamous; that is, a single female and male often together defend a territory and may breed together for a decade or more. Both members of a pair build a large nest out of dead marsh grasses and other plants formed into a mound along the vegetated shores of lakes. A single brood is raised each year from a clutch of one or two olive-brown oval eggs with dark brown spots which are incubated for about 28 days by both parents. Fed by both parents, the chicks fledge in 70 to 77 days. The chicks are capable of diving underwater when just a few days old, and they fly to their wintering areas before ice forms in the fall.

The common loon is assessed as a species of least concern on the IUCN Red List of Endangered Species. It is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds applies. The United States Forest Service has designated the common loon a species of special status because of threats from habitat loss and toxic metal poisoning in its US range.

The common loon is the provincial bird of Ontario, and it appears on Canadian currency, including the one-dollar "loonie" coin and a previous series of $20 bills. In 1961, it was designated the state bird of Minnesota, and appears on the Minnesota State Quarter.

## Appearance

The Common loon is a large aquatic bird that spends most of its life in water and comes out on land only to nest. Breeding adults have a broad black head and neck with a greenish, purplish, or bluish sheen, blackish or blackish-grey upperparts, and pure white underparts. Non-breeding adults are brownish with a dark neck and head marked with dark grey-brown. Their upper parts are dark brownish-grey with an unclear pattern of squares on the shoulders, and the underparts, lower face, chin, and throat are whitish. Males and females look alike, however, males are larger and significantly heavier.

## Distribution

Common loons breed in the northern United States and Canada, as well as in southern parts of Greenland, in Iceland, Svalbard, in Jan Mayen, and in 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 north-east 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.

## Behavior

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.

## Diet

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.

## Reproduction

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.

## Population

### Population threats

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.

### Population number

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.

## Fun Facts

The Common loon is the provincial bird of Ontario, and it appears on Canadian currency, including the one-dollar "loonie" coin and a previous series of $20 bills.

In 1961, the Common loon was designated the state bird of Minnesota and appears in the Minnesota State Quarter.

The Common loon is also known as the Great northern diver in Eurasia. The European name "diver" comes from the bird's practice of catching fish by diving.

Common loons are very clumsy on land, sliding on their belly and pushing themselves forward with their legs. This is because their legs are positioned at the rear of their body; their pelvic muscles are well developed and are ideal for swimming but not well-suited for walking.

When hunting, Common loons normally dive 4 to 10 m (13 to 33 ft), but have been recorded to dive up to 70 m (230 ft)! The average time these birds spend underwater is 42 seconds, but the maximum duration can be about 1 min (60 s).

Common loons often place their nests along steep lake shorelines where adults can quickly dive underwater when approached by predators.

Just like airplanes, Common loons need a long run-up distance to gain momentum for flight take-off. When loons land on water, they skim along on their belly to slow down, rather than braking with their feet, as they are set too far back.

Folk names for the Common loon include "big loon", "call-up-a-storm", "greenhead", "hell-diver", "walloon", "black-billed loon", "guinea duck", "imber diver", "ring-necked loon", and "ember-goose". An old colloquial name from New England was 'call-up-a-storm', as the bird's noisy cries supposedly foretold stormy weather.