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The yodel is a long and complex call made onl

The yodel is a long and complex call made only by the male. It is used in the establishment of territorial boundaries and in territorial confrontations, and the length of the call corresponds with the loon's level of aggression.[65] The dominant frequencies in the yodel indicate the body mass and thereby the health of males.[66] A male that occupies a new territory appears to alter its yodel to be clearly distinguishable from the call of the previous territory owner.[67]

A loon's wail is a long call consisting of up to three notes, and is often compared to a wolf's howl. It uses this call to communicate its location to other loons. The call is given back and forth between breeding pairs or an adult and its chick, either to maintain contact or in an attempt to move closer together after being separated.[63] It is a loud aaoo, weee-wea weee-wea weee-wea, or ooo-aaah-éééé.[2]

The hoot is a short, soft call and is another form of contact call. It is a more intimate call than the wail and is used exclusively between small family groups or flocks.[62] The common loon hoots to let other family or flock members know where it is. This call is often heard when the adult loon is summoning its chicks to feed.[63]

Longevity and terminal investment

Considerable information on longevity and survival rates has been collected in the past two decades, owing to the implementation of an efficient capture protocol that permits marking and monitoring of large study populations.[68] A rough preliminary analysis showed that common loons of both sexes survive at a

A loon's wail is a long call consisting of up to three notes, and is often compared to a wolf's howl. It uses this call to communicate its location to other loons. The call is given back and forth between breeding pairs or an adult and its chick, either to maintain contact or in an attempt to move closer together after being separated.[63] It is a loud aaoo, weee-wea weee-wea weee-wea, or ooo-aaah-éééé.[2]

The hoot is a short, soft call and is another form of contact call. It is a more intimate call than the wail and is used exclusively between small family groups or flocks.[62] The common loon hoots to let other family or flock members know where it is. This call is often heard when the adult loon is summoning its chicks to feed.[63]

Considerable information on longevity and survival rates has been collected in the past two decades, owing to the implementation of an efficient capture protocol that permits marking and monitoring of large study populations.[68] A rough preliminary analysis showed that common loons of both sexes survive at an annual rate of over 90% until they reach their mid-20s,[43] but show a survival rate of only about 75% thereafter. However, a second, finer-scaled analysis made clear that male loons begin to show higher mortality, increased territory loss and lower body condition starting at age 15.[47] Perhaps in response to their physical decline, males 15 and older show increased rates of both territorial aggression and territorial vocalization. This age-related shift in behaviour is interpreted as terminal investment, a "go for broke" strategy seen in senescing animals that are attempting to eke out another year or two of breeding before they die.[47]

Predators and parasites

Adult common loons have few

Adult common loons have few predators, although bald eagles will attack incubating birds. Attacks by sharks in winter have also been recorded.[18] When a predator approaches (either the loon's nest or the loon itself), the common loon sometimes attacks the predator by rushing at it and trying to stab it with its dagger-like bill, aiming its attacks either at the predator's abdomen or the back of its head or neck, which may be deadly to predators up to the size of a fox or raccoon.[69]

Eggs are taken by a number of mammals, including American mink, striped skunk, otters, foxes and raccoons,

Eggs are taken by a number of mammals, including American mink, striped skunk, otters, foxes and raccoons, with the latter being responsible for nearly 40% of all nest failures. Birds such as herring gulls, northern ravens and American crows will eat unattended eggs. Because their nests are at the water's edge, common loon eggs are especially vulnerable if the adult is absent.[18]

Chicks may be killed by common snapping turtles, large gulls, bald eagles and large fish such as northern pike and largemouth bass. The eagle in particular is a significant predator of chicks.[18]

Internal parasites of the common loon include many species of worms, including flatworms, tapeworms, nematodes and spiny-headed worms.[70] High levels of worms may result from feeding changes due to low availability of fish, and can lead to illness and death.[71] Protozoal infections including one caused by Eimeria gaviae[72] and avian malaria have been recorded in this loon.[73] The black fly Simulium annulus is closely associated with the common loon to which it is attracted to chemicals in the uropygial gland secretions as well as by visual and tactile cues. This fly is detrimental to loons, their preferred hosts, transmitting blood-borne parasites and viruses, and causing nest abandonment when numbers are high.[74][75] External parasites include ischnoceran feather lice, although these are not found on the bird's head.[76]

Botulism, acquired by eating infected fish, can lead to paralysis and drowning. Aspergillosis is another cause of emaciation and death.[77] Outbreaks sometimes lead to thousands of deaths.[41]

Since 1998, the common loon has been rated as a species of least concern on the IUCN Red List of Endangered Species. This is because it has a large range – more than 20,000 km2 (7,700 sq mi) – and because it has a stable population trend that does not warrant a vulnerable rating. It also has a large population size of 612,000 to 640,000 individuals. The estimated breeding population ranges from 1,400 to 2,600 mature individuals in Europe.[1] Over half of the breeding population in North America is found in Ontario with 97,000 territorial pairs, and in Quebec with 50,000 territorial pairs. About 2,400 individuals occur in each of the maritime provinces of Canada—Nova Scotia and New Brunswick. British Columbia accounts for 25,000 territorial pairs. In far northern Canada, about 50,000 territorial pairs are known to occur, and 12,500 to 15,000 territorial pairs occur in the Prairie Provinces of Alberta, Manitoba, and Saskatchewan. In the United States, the largest breeding population is present in Alaska with 3,600 to 6,000 territorial pairs. The U.S. Great Lakes region has 5,900 to 7,200 territorial pairs which accounts for over half of the breeding population in the United States. There are about 100 territorial pairs in the northwestern U.S. states of Washington, Idaho, Montana, and Wyoming. About 2,250 territorial pairs are found in New England and New York. In winter, 3,500 to 4,500 individuals are found in the United Kingdom, and even fewer individuals are found in the western European coastline and in Iceland. Along the Pacific Coast, about 184,000 to 189,000 adults and 31,000 to 32,000 juveniles are found, and along the Atlantic Coast, 423,000 to 446,000 adults and 72,000 to 76,000 juveniles are found.[18]

The common loon is listed under Appendix II of the Convention on the Conservation of Migratory Species, and in Article I under the European Union (EU) Convention on the Conservation of Migratory Species, and in Article I under the European Union (EU) Birds Directive.[1] It is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) is applied.[78] In Europe it appears in 20 Important Bird Areas (IBAs), including Ireland, Svalbard, mainland Norway, Iceland, Spain, and the United Kingdom. It is also a listed species in 83 Special Protection Areas in the EU Natura 2000 network.[1] The USDA National Forest Service has designated the common loon a species of special status, and in the upper Great Lake regions of the Huron-Manistee, Ottawa, and Hiawatha national forests as a regional forester sensitive species.[79]

The effects of mercury and acid rain pollution are considered to be among some of the most important factors in the reproductive success of common loons.[80][81] Across the upper United States and lower Canada, studies have shown that lake acidity tends to increase from west to east[80] likely stemming from fossil fuel combustion that releases mercury and other harmful components of acid rain which are then moved eastward by prevailing winds.[81] Acidification of lakes can lead to decreases in the availability of important elements such as calcium while increasing the mobility of toxic metals such as mercury and lead.[82]

Generally, mercury is most commonly found as methylmercury in nature.[80] Acid rain and mercury levels in aquatic environments are positively correlated as increases in acid rain lead to elevated levels of sulfur oxides that are used by sulfate-reducing bacteria to enhance methylmercury production.[80] Mercury levels and pH are also correlated as experiments have shown that increases in pH are correlated with a decrease in mercury levels.[83] Methylmercury levels are then passed from organism to organism through the Generally, mercury is most commonly found as methylmercury in nature.[80] Acid rain and mercury levels in aquatic environments are positively correlated as increases in acid rain lead to elevated levels of sulfur oxides that are used by sulfate-reducing bacteria to enhance methylmercury production.[80] Mercury levels and pH are also correlated as experiments have shown that increases in pH are correlated with a decrease in mercury levels.[83] Methylmercury levels are then passed from organism to organism through the food chain with the species at the top being the most effected.[83] In this case, mercury levels are passed in the order of crayfish, zooplankton, pre fish, fish and then the common loon.[84] Resulting from this transmission of mercury, there is a significant positive correlation between mercury levels in fish and mercury levels in male, female, and chick blood of common loons; consequently, an increase in mercury concentration in the blood of common loons and fish was seen with a decrease in pH.[83] Related to this information, it was discovered that mercury concentration differs by sex and age of common loons. Male common loons were found to contain the highest blood mercury concentration likely due to the fact that they tend to consume bigger fish with higher mercury concentrations.[85] Females contained the second highest blood mercury concentration with differences between the males likely being due to the fact that females can expel mercury into the eggs they lay.[83] Juveniles had the lowest blood mercury concentration.[86] Scientists found that the data from juveniles helped to best indicate the local mercury availability as they are fed exclusively from their natal territory.[83]

Elevated levels of mercury have been associated with changes in foraging as well as brooding behavior among adult common loons, especially in higher concentrations.[86] Studies have deduced that elevated levels of mercury in the blood of common loons have detrimental effects on brood productivity. One such study found that brood productivity was reduced by half when female blood mercury levels exceeded 4.3 μg/g and productivity completely failed when female blood mercury levels exceeded 8.6 μg/g. These results are related to fish mercury levels of 0.21 μg/g and 0.41 μg/g, respectively.[86] As mercury levels and pH are correlated, scientists have found that brood success decreases with decreasing pH such that environments with a pH at around 4.5 exhibited reproductive success below a calculated positive growth rate threshold.[80]

Due to elevated mercury levels in lakes that common loons inhabit, many studies have revealed that a large number of common loons tested are at high risk for detrimental impacts on health and reproduction. One study in the Adirondack Mountains in central New York showed that 21% of male and 8% of female common loons were at high risk for detrimental impacts.[85] In addition, a study conducted on common loons in Québec, Canada determined that 33% of the loons tested were at high risk for detrimental effects on health and reproduction.[83] Although there have been reductions in recent years in acidifying emissions, there has been limited biological recovery in these lakes most likely due to climate change.[80] Research has shown that warmer summer temperatures can inhibit reestablishment of cold-water fish species in acidified lakes and droughts brought on by increased summer temperatures can further acidify lakes.[80]

The common loon's breeding range has moved northward, the species breeding as far south as Iowa a century ago.[87] It too is adversely affected by acid rain and pollution, as well as lead poisoning from fishing sinkers (especially those that are about the size of the grit stones they ingest[88]) and mercury contamination from industrial waste.[89] Heavy metals such as mercury may be partially removed through biological processes such as excretion or deposition in feathers, but their adverse effects are magnified through concentration of the toxic elements in organs such as the liver. Eggs shells may also contain metal contaminants,[90] leading to low reproductive productivity. High levels of heavy metals are linked to loons being in poor condition,[91] males being affected more because they eat larger fish.[41]

The common loon has also faced a decline in breeding range due to hunting, predation, 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 in the loon

The common loon has also faced a decline in breeding range due to hunting, predation, 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 in the loon's breeding territories.[92] In addition, artificial floating nesting platforms have been provided for the common loon in some lakes to reduce the impact of changing water levels due to dams and other human activities.[93] The common loon abandons lakes that fail to provide suitable nesting habitat due to shoreline development. It is endangered by personal water-craft and powerboats that may drown newly born chicks, wash eggs away, or swamp nests.[87] It is still considered an "injured" species in Alaska as a result of the Exxon Valdez oil spill.[79]

The voice and appearance of the common loon has made it prominent in several Native American tales. These include an Ojibwe story of a loon that created the world,[94] and a Micmac saga describing Kwee-moo, the loon who was a special messenger of Glooscap (Glu-skap), the tribal hero.[95] The tale of the loon's necklace was handed down in many versions among Pacific Coast peoples.[96] The Delaware in the east of North America and the Buryats of Siberia also had creation stories involving the loon.[97]

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",[98] and "ember-goose".[99] An old colloquial name from New England was call-up-a-storm, as its noisy cries supposedly foretold stormy weather.[100] Some old Scottish names such as arran hawk and carara are corruptions of old Scottish Gaelic onomatopoeic names representing the bird's call; others, like bishop and ember goose, were used to avoid older names for this sometimes ill-omened bird.[101]

The common loon was eaten in the Scottish Islands from the Neolithic until the eighteenth century, and its thick layer of fat beneath the skin was used as a cure for [98] and "ember-goose".[99] An old colloquial name from New England was call-up-a-storm, as its noisy cries supposedly foretold stormy weather.[100] Some old Scottish names such as arran hawk and carara are corruptions of old Scottish Gaelic onomatopoeic names representing the bird's call; others, like bishop and ember goose, were used to avoid older names for this sometimes ill-omened bird.[101]

The common loon was eaten in the Scottish Islands from the Neolithic until the eighteenth century, and its thick layer of fat beneath the skin was used as a cure for sciatica.[97]

The common loon appears on Canadian currency, including the one-dollar "loonie" coin and the previous series of $20 bills.[102] It is the provincial bird of Ontario.[103] It was designated the state bird of the U.S. state of Minnesota in 1961,[104] and also appears on the Minnesota State Quarter.[105] Major League Soccer club Minnesota United FC uses the loon in its crest and nickname.[106]

The wailing call of the loon is widely used in film and television to evoke wilderness and suspense, and is referenced in songs such as "Old Devil Moon" ("wanna laugh like a loon").[97]

This bird is central to the plot of the children's novel Great Northern? by Arthur Ransome (in which it is referred to throughout as "great northern diver", with the obsolete scientific name Colymbus immer). The story is set in the Outer Hebrides, where the main characters—a group of children on holiday—notice a pair of divers apparently nesting there. Checking their bird book, they believe that these are great northern divers. However, these have not previously been seen to nest in northern Scotland, and so they ask for help from an ornithologist. He confirms that these birds are indeed the great northern; unfortunately, it soon transpires that he does not wish merely to observe, but wants to steal the eggs and add them to his collection; and to do this, he must first kill the birds. Published in 1947, the story is one where the conservationists are the eventual victors over the egg collector, at a time when the latter hobby was not widely considered to be harmful.[107][108]

In the 2016 Pixar movie Finding Dory, a somewhat bedraggled and dimwitted loon named Becky is persuaded to use a bucket to help two of the main characters, Nemo and Marlin, get into a marine life institute where the titular Dory is trapped.[109] Loons are also featured prominently in the 1981 film On Golden Pond.[110]