Physical characteristics
Loons are medium to large, foot-propelled diving waterbirds,with anatomy specialized for pursuit and capture of fish.Overall shape is very distinctive with a short neck, pointed wings, and legs set far back on the body. Loon tarsi are flattened and knife-like, cutting through the water efficiently.The feet are large and palmate with the front three toes webbed, and a free hallux. Loon feet, legs, and nails are uniquely countershaded such that when swimming white surfaces,the tops of their feet are oriented down, helping the bird blend in against light sky. Bills are medium-sized and dagger-like. All species have a distinct blood red iris in alternate plumage. Sexes are similar, with the male larger than the female in all species. Each species has four plumages after they are fully grown: juvenal, second alternate (second summer), basic (nonbreeding), and alternate (breeding). Molt times are slightly different for all species. In alternate plumage all species have striking patterns composed of black, white, and gray. Upperparts are dark gray or black, with faint white speckling to bold white checkering. Underparts are completely white. Each species has a series of bold, thin, black-and-white parallel stripes on the neck. Head patterns are similar in Arctic/Pacific loons and common/ yellow-billed loons. The head pattern of red-throated loon is unique: it is the only loon to have brick red in its plumage.

Loons breed in freshwater inland lakes and tundra ponds.Where sympatric, different species occupy different-sized lakes.Larger species exclude smaller species from breeding ponds,but are limited to larger ponds by minimum take-off distances.Smaller species can occupy ponds too small for larger species.


Individuals usually spend winter near shore in oceans and seas,less than 62 mi (100 km) offshore. They are occasionally found in large freshwater lakes and rivers during winter.

Loons are extremely territorial on their breeding grounds.Pairs have been observed attacking their own species, as well as other species of loons, ducks, and geese. In one study, 50% of common loons had healed fractures believed to have been caused by the bill of other common loons. Loon pairs have a
series of territorial threat postures and calls to prevent fighting,which can be fatal. In winter and during migration loons may be found singly or in loose flocks. Loons are known for their unusual vocalizations, described as yodels, wails, and tremolos. Most vocalizations are given on the breeding grounds, occasionally during winter, or on migration.


 Territorial yodels, most often given at night or early morning, can be heard from great distances (reports have been made of calls heard up to 16 mi [25.8 km] by humans).These male yodels are individually recognizable throughout the birds’ lifetime.Flight is powerful and direct, with wings beating constantly.Most species require running on the surface of water to gain speed for take-off. The red-throated loon is the only species that can take off from land. All species are awkward on land; the posterior positioning of the feet often forces them to push themselves along breast first on their bellies. Occasionally loons accidentally land on wet pavement after mistaking it for water, or are forced to land during storms. In this case, they are stranded and will most likely die, although adults in this situation have traveled over a kilometer to seek
water at the expense of broken toes and wrists.


Feeding ecology and diet
Loons take a variety of vertebrate and invertebrate foods,but small to medium-sized fish up to about 7–8 in (18–20 cm) are the primary items. Young are also fed crustaceans, mol-lusks, and worms. Prey is located by sight from the surface of the water. Loons peer downward, often with their bill in the water, and dive with a thrust from both feet. Most prey is eaten underwater; fish that are too large to be handled underwater are taken to the surface. Most foraging is done close to the surface, but loons may forage as deep as 230 ft (70 m) if the water is clear enough. Very small serrations on the bill help loons hold onto prey. Adults and young consume large quantities of prey; an adult common loon consumes 1,214 kilocalories a day, and a pair may eat 2,000 lb (910 kg) of fish in a breeding season. Loons have large salt glands that remove excess salt consumed from marine environments. Stomach contents have shown that loons consume a wide variety of fish, including sticklebacks (Gasterosteus), trout (Salvelinus), sculpin (Leptocottus), cods (Gadus), herrings (Clupeiidae), haddock (Melanogrammus), whitefish (Coregonus), capelins (Mallotus), minnows (Cyprinidae), and many other species. At sea, menhaden (Brevoortia) are extremely important. Little is known about prey selection.

Reproductive biology
Loons are monogamous, although they will quickly replace a lost mate. Extra-pair copulation has been noted with marked birds, but has not been studied extensively to determine frequency. Pair bonds, which may last for life, are first formed on breeding grounds. Pair formation is not well understood, although it includes bill-dipping and paired-swimming displays where both adults rise out of the water in various postures. Both sexes quickly build the nest, sometimes in as little as half a day to a week; returning pairs may reuse old nests. Nests are constructed of wet vegetation on land or as a floating mat, with a 15–32 in (38–82 cm) diameter. Two eggs are usually laid (rarely one or three) from May to July, depending on latitude and weather; in northernmost areas there may be only two to three months to breed. Eggs are long, subelliptical in shape, from 2.9 by 1.8 in (72.7 by 44.8 mm) to 3.5
by 2.2 in (89.4 by 55.15 mm) in size, and are olive green with brown markings. Pairs will re-lay if the first clutch is lost. Both sexes incubate, beginning with the laying of the first egg. Incubation period is 24–30 days; larger species have longer incubation periods. Chicks hatch asynchronously, are semiprecocial, and covered with dark gray natal down. Chicks leave the nest soon after they dry, but may return for brooding. 


Young rely on both parents for food but will begin to dive on their own in three days. Chicks will occasionally ride on a parent’s back when small. Young can fly in six to eight weeks. Predators of eggs and chicks include many mammals and other birds. To avoid predators, chicks dive to the bottom of the water to stir up sediments, resurfacing in emergent vegetation for cover. 


Adults have few predators, and band recoveries suggest loons have a life span of 25–30 years.

Conservation status
No loons are listed on the IUCN Red List of Threatened Species of Birds. Isolation of breeding habitat protects their numbers from human disturbance in many areas, but where overlap does occur loons have declined due to habitat encroachment and acid precipitation, which can lower pH levels enough to kill all the fish in many lakes. Loon conservation groups have formed to protect them in many areas. At sea, fishnets kill many adults, and are responsible for one-third of red-throated loon banding recoveries. Oil spills kill many loons, which are especially susceptible when adults are flightless while molting primaries. The Exxon Valdez spill in Alaska resulted in hundreds of loons being washed ashore. Botulism, a bacterial disease, has killed thousands of loons staging on the Great Lakes. Common loon populations, in particular, have declined in parts of northeastern United States and in Ontario, Canada, due to increase in human activities—boating, use of jet skis, and canoeing—lake acidification, and mercury poisoning.


Significance to humans
The Inuit legally hunt loons in arctic North America for subsistence purposes. Roughly 4,600 may be taken each year. They are not considered to be the best-tasting food, and may be fed to dogs. Native Americans honor loons with many stories and parables. Loons are a symbol of the north, and a symbol of tranquility. The common loon is featured in Canadian currency on the $1 coin (commonly called “loonies”) and the $20 bill.