page_title: Common loon
section_title: Breeding
hierarchical_section_title: Common loon / Behaviour / Breeding
caption_attribution_description: English: Coloured Figures of the Eggs of British Birds - Seebohm Great Northern Loon Gavia immer
context_page_description: The common loon or great northern diver 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; 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.
context_section_description: The common loon's mating system is serially monogamous; breeding pairs jointly defend a territory consisting of an entire small lake or a protected bay within a large lake. A given male and female remain together throughout a breeding attempt, rear their own biological offspring, reunite each spring, and may breed together for many consecutive years. However, in the event of death or territorial eviction of one pair member by an intruding loon of the same sex, the other pair member quickly establishes a pair bond with the evicting bird. (Hence, most adult loons have two or more different mates during their lives.) Evicting individuals tend to be young males and females (5 to 9 years old), while evicted adults are often those 15 years and older.
  Pairs do not remain together during winter; in addition, males usually precede females by a few days to a few weeks during spring migration, settling on their lake once a portion of it becomes ice-free. Copulation takes place ashore, often on the nest site, repeated daily until the eggs are laid. The preceding courtship is very simple, with mutual bill-dipping and dives. The displays towards intruders, such as bow-jumping (an alternation of fencing and bill-dipping postures and rushing (running "along the surface with its wings either folded or half-extended and flapping at about the same speed as when taking off") are often misinterpreted as courtship.
  Nesting typically begins in early May. Significantly more nesting sites are found on islands than on mainland shoreline. Breeding pairs patrol their territories routinely, even at night, defending the territory both physically and vocally. Pairs that nested together the preceding year typically reuse the nest site from the previous year, if they hatched chicks successfully there. In contrast, pairs that lost their eggs to a predator usually shift the nest to a new location. This logical behaviour pattern appears to depend upon the male, because breeding pairs consisting of last year's male and a female not present during the preceding year continue to exhibit the behaviour; pairs composed of last year's female and a new male tend to select a new nest site, regardless of the success or failure of the previous year's attempt. Despite the lead role of males in nest site selection, both sexes contribute substantially to nest construction. The nest is about 56 cm (22 in) wide and is constructed out of dead marsh grasses and other indigenous plants, and formed into a mound along the vegetated coasts of lakes greater than 3.7 ha (9.1 acres). 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. Based on a number of studies, nesting success averages about 40%, and most newly hatched young survive due to parental care.
  Eggs from first clutches are typically laid in May or early June, the timing depending largely upon the date that lakes become ice-free and inhabitable. A clutch consists of two (occasionally one) olive-brown oval eggs with dark brown spots. Incubation is carried out jointly by male and female and lasts about 28 days. Loons often place nests along steep lake shorelines where adults can quickly dive underwater when approached by predators. The eggs are about 88 mm (3.5 in) long and 55 mm (2.2 in) wide and the two eggs are laid with an interval of one to three days between them, and hatch asynchronously.
  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. Parents and chicks initially stay in shallow, isolated bays where the parents are able to defend the chicks better from intruding loons and eagles, which are their main predators. Male parents defend broods consisting of two chicks more vigorously than singleton chicks, chiefly with the territorial yodel call. 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
caption: Egg
exif: {}