Editing Common loon

{{short description|Freshwater bird native to North America and Western Europe}}
{{Lead rewrite|date=May 2025}}
{{good article}}
{{speciesbox
| image = Gavia immer -Minocqua, Wisconsin, USA -swimming-8.jpg
| image_caption = Adult in breeding plumage in [[Minocqua, Wisconsin]]
| image2 = Loon, common 04-24 a.jpg
| image2_caption=In non-breeding plumage in [[Sunset Beach, North Carolina]]
| status = LC
| status_system = IUCN3.1
| status_ref = <ref name="iucn status 19 November 2021">{{cite iucn |author=BirdLife International |date=2018 |title=''Gavia immer'' |volume=2018 |page=e.T22697842A132607418 |doi=10.2305/IUCN.UK.2018-2.RLTS.T22697842A132607418.en |access-date=19 November 2021}}</ref>
| genus = Gavia
| species = immer
| authority = ([[Morten Thrane Brünnich|Brünnich]], 1764)
| range_map = Gavia immer map 2.svg
| range_map_caption = Approximate distribution map
{{leftlegend|#ff6600|Breeding}}
{{leftlegend|#ffd42a|Migration}}
{{leftlegend|#5f8dd3|Nonbreeding}}
| synonyms = *''Colymbus immer'' {{small|Brunnich, 1764}}
*''Colymbus glacialis'' {{small|Linnaeus, 1766}}
| synonyms_ref = <ref name="hbw2" />
}}

The '''common loon''' or '''great northern diver''' ('''''Gavia immer''''') is a large member of the [[loon]], or diver, [[family (biology)|family]] of birds. [[Reproduction|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 [[Anatomical terms of location|underparts]] except some black on the [[undertail covert]]s 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, [[crustacean]]s, insect larvae, [[Mollusca|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 [[Monogamy in animals|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 [[Hymenachne|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 [[Bird egg|eggs]] with dark brown spots which are [[Egg incubation|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 species|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 [[List of Canadian provincial and territorial symbols|provincial bird]] of [[Ontario]], and it appears on Canadian currency, including the [[Loonie|one-dollar "loonie"]] coin and a previous series of [[Canadian twenty-dollar note|$20 bills]]. In 1961, it was designated the [[List of U.S. state birds|state bird]] of [[Minnesota]], and appears on the Minnesota [[State Quarter]] and the state [[Seal of Minnesota]].

==Taxonomy==
The common loon is also known as the great northern diver in [[Eurasia]]. Another former name, great northern loon, was a compromise proposed by the [[International Ornithological Committee]].<ref>{{Cite book|url=https://books.google.com/books?id=OiaNDAAAQBAJ&pg=PA13|title=Handbook of Bird Biology|last1=Lovette|first1=Irby J.|last2=Fitzpatrick|first2=John W.|date=2016|publisher=John Wiley and Sons|isbn=978-1-118-29104-7|location=New York, NY|pages=13}}</ref> It is one of five [[loon]] species that make up the [[genus]] ''Gavia'', the only genus of the family Gaviidae and order [[Gaviiformes]]. Its closest relative is another large black-headed species, the [[yellow-billed loon]] or white-billed diver (''Gavia adamsii'').<ref name="Boertmann">{{cite journal|last=Boertmann|first=D.|year=1990|title=Phylogeny of the divers, family Gaviidae (Aves)|url=https://www.researchgate.net/publication/258846478| journal=Steenstrupia|volume=16|issue=3|pages=21–36}}</ref> There are no recognized subspecies of the common loon.<ref>{{cite web | editor1-last=Gill | editor1-first=Frank | editor1-link=Frank Gill (ornithologist) | editor2-last=Donsker | editor2-first=David | year=2018 | title=Loons, penguins, petrels | work=World Bird List Version 8.2 | url=https://www.worldbirdnames.org/bow/loons/ | publisher=International Ornithologists' Union | access-date=12 November 2018 | archive-url=https://web.archive.org/web/20200427191432/https://www.worldbirdnames.org/bow/loons/ | archive-date=27 April 2020 | url-status=dead }}</ref>

Danish [[zoologist]] and [[mineralogist]] [[Morten Thrane Brünnich]] first described the common loon in 1764, as ''Colymbus immer'' in his ''Ornithologia Borealis''.<ref>{{cite book|url=https://www.digitale-sammlungen.de/en/view/bsb10306825?page=50|title=Ornithologia Borealis|last=Brünnich|first=Morten Thrane|publisher=J.C. Kall|year=1764|location=Hafnia (Copenhagen) |page=38|language=la|author-link=Morten Thrane Brünnich}}</ref> The now-defunct genus ''Colymbus'' contained [[grebe]]s as well as loons,<ref name =shuf>{{Cite journal|last=Shufeldt|first=R.W. |date=1914|title=On the oology of the North American Pygopodes | journal=The Condor | volume=16| issue=4| pages=169–180| doi=10.2307/1362079| jstor=1362079 | url=https://sora.unm.edu/sites/default/files/journals/condor/v016n04/p0169-p0180.pdf }}</ref> and remained in use{{efn|For example, [https://britishbirds.co.uk/wp-content/uploads/article_files/V43/V43_N01/V43_N01_P008_008_A003.pdf this] 1951 ''British Birds'' article}} until the [[International Commission on Zoological Nomenclature]] attempted to clarify the nomenclature in 1956 by declaring ''Colymbus'' a suppressed name unfit for further use and establishing ''Gavia'', created by [[Johann Reinhold Forster]] in 1788, as the valid genus name for the loons.<ref name=ICZN>{{cite journal|author=International Commission on Zoological Nomenclature|author-link=International Commission on Zoological Nomenclature|year=1957–58|title=The family-group names "Gaviidae" Coues, 1903 and "Urinatoridae" (correction of "Urinatores)" Vieillot, 1818 (Class Aves) – "Opinion" 401 and "Direction" 75|journal=Bulletin of Zoological Nomenclature|volume=15A|pages=147–48|url=https://biodiversitylibrary.org/page/12218706}}</ref>

The current genus name ''Gavia'' was the Latin term for an unidentified seabird and the specific ''immer'' is derived from a Norwegian name for the bird,<ref name=job>{{cite book | last=Jobling | first= James A. | year= 2010| title=The Helm Dictionary of Scientific Bird Names | url=https://archive.org/details/Helm_Dictionary_of_Scientific_Bird_Names_by_James_A._Jobling | publisher= Christopher Helm | location=London | isbn=978-1-4081-2501-4 | pages=[https://archive.org/details/Helm_Dictionary_of_Scientific_Bird_Names_by_James_A._Jobling/page/n171 171], 203}}</ref> similar to the modern Icelandic word "himbrimi".{{sfn|Johnsgard|1987|p=94}} The word may be related to Swedish ''immer'' and ''emmer'': the grey or blackened ashes of a fire (referring to the loon's dark plumage); or to Latin ''immergo'', to immerse, and ''immersus'', submerged.{{sfn|Johnsgard|1987|p=107}}

The European name "diver" comes from the bird's practice of catching fish by diving.<ref name=OEDdiver>{{OED |Diver}}</ref> The North American name "loon" was first recorded in this sense in ''New Englands Prospect'' (1634) by William Wood (1580–1639); "The Loone is an ill shap'd thing like a Cormorant".<ref name=OEDloon>{{OED |Loon}}</ref><ref>{{ cite book | last=Wood | first=William | year=1865 | orig-year=1634 | title=Wood's New-England's Prospect | location=Boston | publisher=Prince Society | page=[https://archive.org/details/woodsnewengland00woodgoog/page/n83 34] | url=https://archive.org/details/woodsnewengland00woodgoog }}</ref> It may be derived from Old Norse ''lómr'', as are modern Swedish and Danish ''lom'',<ref name=OEDloom>{{OED |Loom}}</ref> in each case referring to the distinctive call.{{sfn|Lockwood|1984|p=97}}

A number of fossil loon species are known from the [[Pliocene]], and specimens from the [[Pleistocene]] of [[California]] and [[Florida]] appear to represent a [[paleosubspecies]] of the common loon.<ref>{{cite journal|last1=Brodkorb|first1=Pierce|year=1953|title=A review of the Pliocene loons|journal=Condor|volume=55|issue=4|pages=211–14|url=http://sora.unm.edu/sites/default/files/journals/condor/v055n04/p0211-p0214.pdf|doi=10.2307/1364769|jstor=1364769|access-date=4 September 2017|archive-date=18 January 2021|archive-url=https://web.archive.org/web/20210118012151/https://sora.unm.edu/sites/default/files/journals/condor/v055n04/p0211-p0214.pdf|url-status=dead}}</ref>

==Description==
[[File:Gavia immer -Marshfield, Vermont, USA -flying-8 (5).jpg|thumb|In flight]]The adult common loon can range from {{Convert|66|to|91|cm|in|abbr=on}} in length with a {{Convert|127|to|147|cm|ftin|0|abbr=on}} [[wingspan]],<ref name="hbw2">{{cite journal|url=http://www.hbw.com/species/common-loon-gavia-immer|title=Common Loon (''Gavia immer'')|last1=Carboneras|first1=C|last2=Christie|first2=D.A.|year=2021|editor1-last=del Hoyo|editor1-first=Josep|editor2-last=Elliott|editor2-first=Andrew|journal=Handbook of the Birds of the World Alive|publisher=Lynx Edicions|access-date=7 November 2016|url-access=subscription |last3=Garcia|first3=E.F.J. |doi=10.2173/bow.comloo.02 |editor3-last=Sargatal|editor3-first=Jordi|editor4-last=Christie|editor4-first=David A.|editor5-last=de Juana|editor5-first=Eduardo}}</ref> slightly smaller than the similar yellow-billed loon.<ref name="Evers2010" /> On average, it is about {{Convert|81|cm|in|abbr=on}} long and has a [[wingspan]] of {{Convert|136|cm|in|abbr=on}}. Its weight can vary anywhere from {{Convert|2.2|to|7.6|kg|lb|abbr=on}}.<ref name=":72">{{Cite book|title=Threatened, endangered, and sensitive species of the Intermountain region| last=Spahr| first=Robin| date=1991| publisher=[[United States Department of Agriculture]], [[U.S. Forest Service|Forest Service]], Intermountain Region| pages=115–116}}</ref><ref name= Evers>Evers, D. C., J. D. Paruk, J. W. McIntyre, and J. F. Barr (2010). ''Common Loon (Gavia immer)'', version 2.0. In The Birds of North America (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA.</ref> Sizes vary regionally, especially by body mass, with the smallest bodied loons on average from lower-central [[Canada]] and the [[Great Lakes|Great Lake]]s, while westerly birds are similar or mildly larger, and loons breeding further east can appear to be significantly larger. Furthermore, males average up to nearly 27% more massive than females in some populations.<ref>Storer, R. W. (1988b). ''Variation in the Common Loon (Gavia immer)''. In Papers from the 1987 Conference on Common Loon Research and Management., edited by P. I. V. Strong, 54–65. Meredith, NH: North American Loon Fund.</ref> Breeding loons in [[Maine]] averaged {{convert|4.65|kg|lb|abbr=on}} in females and {{convert|5.97|kg|lb|abbr=on}} in males, essentially the same weight as the yellow-billed loon, although the yellow-billed is still larger than in linear dimensions (especially bill length) than the Maine loons.<ref name= Evers/> In [[Ontario]], 20 females averaged {{convert|4.5|kg|lb|abbr=on}} and 20 males averaged {{convert|5.46|kg|lb|abbr=on}}.<ref>{{cite book |title=CRC Handbook of Avian Body Masses |edition=2nd |editor-first=John B. Jr. |editor-last=Dunning |publisher=CRC Press |year=2008 |isbn=978-1-4200-6444-5}}</ref> In contrast, in the [[Gulf of Alaska]], adults of both sexes reportedly averaged {{convert|4.13|kg|lb|abbr=on}}.<ref>Hunt Jr, G. L., Drew, G. S., Jahncke, J., & Piatt, J. F. (2005). ''Prey consumption and energy transfer by marine birds in the Gulf of Alaska''. Deep Sea Research Part II: Topical Studies in Oceanography, 52(5-6), 781–797.</ref> Adult [[Reproduction|breeding]] [[plumage]] consists of a broad black head and neck with greenish, purplish, or bluish sheen.<ref name="hbw2" /> It has a black [[Beak|bill]] sometimes with a pale tip, and [[iris (anatomy)|red eyes]].<ref name="hbw2" /><ref name=":72" /> The neck is encircled with a characteristic black ring<ref name=":62">{{Cite book|title=Pete Dunne's Essential Field Guide Companion: A Comprehensive Resource for Identifying North American Birds| last=Dunne| first=Pete| date=2013| publisher=Houghton Mifflin Harcourt| isbn=978-0-544-13568-0 | page=89}}</ref> 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.<ref name="hbw2" /><ref name=":72" /> 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 the long black shaft-streaks on the axillaries. The [[Anatomical terms of location|underparts]] are pure white, but have some black on the undertail coverts and vent.<ref name="hbw2" /> It has a checkered black-and-white [[Glossary of bird terms#mantle|mantle]]<ref name=":62" /> 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.<ref name="hbw2" />
[[File:2012 Photo Contest - Wildlife Category (7944829792).jpg|thumb|Common loon stretching]]

Adult non-breeding plumage is brownish with a dark neck and head marked with dark grey-brown.<ref name="hbw2" /><ref name=":62" /> The eyes are surrounded with white,<ref name="hbw2" /> and the eyelids are pale.<ref name=":62" /> 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 wedge-shaped notch in dark neck-sides,<ref name="hbw2" /> and may sometimes reveal a shadowy trace of the neck ring or a pale collar.<ref name=":62" /> 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,<ref name="hbw2" /> although they exhibit sexual dimorphism in their physical dimensions with the male larger and significantly heavier than the female.<ref name="Evers2010" />

The heavy dagger-like bill<ref name=":72" /> is evenly tapered and greyish, sometimes having a black tip.<ref name=":62" /> The bill colour and angle distinguish this species from the yellow-billed loon. The neck is short and thick.<ref name=":62" /> The common loon swims very low in the water, with sometimes only its head held above and horizontal to the surface.<ref name=":72" /> It must run across the water surface to get in flight. During flight, its head is slightly lower than its body, with its feet trailing behind.<ref name=":72" /> It has a skeletal structure made up of a number of solid bones (this is usual for the Gaviiformes and penguins<ref>{{Cite journal|last=Smith|first=Nathan D.|year=2012|title=Body mass and foraging ecology predict evolutionary patterns of skeletal pneumaticity in the diverse "waterbird" clade | journal=Evolution | volume=66 |issue=4 | pages=1059–1078 | doi=10.1111/j.1558-5646.2011.01494.x |pmid=22486689|s2cid=42793145|doi-access=free }}</ref> but unlike most flying birds which have [[bird skeleton|bones]] with extensive pneumatization, hollow and filled with air to make the skeleton lighter), which adds weight but helps in diving.<ref name="Wisconsin Natural Resources"/>
[[File:Common Loon in Maine RWD.jpg|thumb|Juvenile off Mcgee Island, [[Maine]]]]
A juvenile often has a dark, brownish-grey nape that may look darker than the pale-edged black feathers.<ref name=":122">{{Cite book |title=Kaufman Field Guide to Advanced Birding: Understanding What You See and Hear|last=Kaufman|first=Kenn|date=2011| publisher=Houghton Mifflin Harcourt|isbn=978-0-547-24832-5|location=Boston, MA|pages=171–172}}</ref> It has a dark grey to black head, neck, and upperparts, with white throat, cheeks, and underparts.<ref name=":72" /> During the first winter, the bill shape of the young may not be as fully developed as that of the adult,<ref name=":122" /> and during the second winter, it much resembles the breeding adult, but with wing coverts lacking white spots.<ref name="hbw2" />

The common loon is distinguished from the [[black-throated loon]] (''G. arctica'') and the [[red-throated loon]] (''G. stellata'') mainly by its larger size. It usually has a steeper forehead and a bulging forecrown, somewhat similar to the black-throated loon. Its bill is heavier and the back is paler than its hindneck. It is more difficult to separate from the yellow-billed loon, but its breeding plumage has more white markings on the neck and the squares on its shoulders are usually smaller; the non-breeding plumage has darker neck-sides contrasting more sharply with pale areas and bill colour.<ref name="hbw2" />

===Moult===

The scaly juvenile plumage is retained until January or February of the year following hatching, when a lengthy moult of head and body feathers gives them a more adult-like appearance. Adults shed all their flight feathers simultaneously around this time, leaving them temporarily flightless, prior to gaining breeding plumage, but second-year birds delay this substantial moult until the summer. The adult winter plumage is attained between October and January by partial moult mainly of head, body and tail feathers.<ref name= BB79>{{cite journal | last1=Appleby | first1=R.H. | last2=Madge | first2=S.C. | last3=Mullarney | first3=Killian | title=Identification of divers in immature and winter plumages | journal=British Birds | volume=79 | issue=8 | pages=365–391 | year=1986 | url=https://britishbirds.co.uk/wp-content/uploads/article_files/V79/V79_N08/V79_N08_P365_391_A089.pdf | access-date=8 October 2017 | archive-date=8 October 2017 | archive-url=https://web.archive.org/web/20171008180556/https://britishbirds.co.uk/wp-content/uploads/article_files/V79/V79_N08/V79_N08_P365_391_A089.pdf | url-status=dead }}</ref>

=== Genomics ===
With improved [[gene]]-sequencing technology, a draft [[genome]] of the common loon has assembled and identified at least 14,169 genes. 80.7% of chicken genes are found in the common loon genome. The physiological costs of deep-water diving and long distance aerial migration of loons have greatly affected loon evolution. Many identified genes are candidate genes for positive selection since the common loon-chicken split 90 million years ago. It is theorized that these candidate genes are related to [[haemoglobin]] affinity for oxygen, solute exchange, [[immunoglobulin]] function related to immune defence, [[nervous system]] development and a number of molecular pathways related to DNA metabolic function, and G-receptor pathways potentially involved in low-light visual acuity. For example, SLC48A, and SLC20A1 are candidate genes in the ''Gavia'' lineage for maintaining [[homeostasis]] due to maybe having a role in maintaining ion and pH balance.<ref>{{cite journal | pmc=5921391 | year=2018 | last1=Gayk | first1=Z. G. | last2=Le Duc | first2=D. | last3=Horn | first3=J. | last4=Lindsay | first4=A. R. | title=Genomic insights into natural selection in the common loon (Gavia immer): Evidence for aquatic adaptation | journal=BMC Evolutionary Biology | volume=18 | issue=1 | page=64 | doi=10.1186/s12862-018-1181-6 | pmid=29703132 | doi-access=free | bibcode=2018BMCEE..18...64G }}</ref>

==Distribution and habitat==
Common loons are mainly [[Nearctic realm|Nearctic]], and breed from [[49th parallel north|48° N]] to the [[Arctic Circle]], locally south to [[40th parallel north|40° N]] and north to [[78th parallel north|78° N]].<ref name="hbw2" /> During their breeding season in spring and summer, most common loons live on lakes and other waterways in the northern United States and Canada, as well as in southern parts of [[Greenland]],<ref name=bwp/> in Iceland, in [[Svalbard]], in [[Jan Mayen]], and in [[Bear Island (Norway)|Bear Island]] in Norway; and in [[Alaska]], to the west, and very rarely in [[Scotland]], to the east.<ref name="hbw2" /> Their summer habitat ranges from wooded lakes to [[tundra]] ponds. The lakes must be large enough for flight take-off, and provide a large population of small fish.<ref name=bwp>{{cite book | editor1-last = Snow | editor1-first = David |editor2-last=Perrins|editor2-first=Christopher M.| title = The Birds of the Western Palearctic (BWP) concise edition (2 volumes) | publisher=Oxford University Press |year = 1998| location=Oxford | isbn= 978-0-19-854099-1 |pages=8–10| title-link = The Birds of the Western Palearctic }}</ref> Deep lakes with warm surface waters, relatively low biological productivity and low turbidity where their fish prey are easy to see are habitats where breeding loons are more successful in raising young.<ref>{{Cite journal|last1=Thompson |first1=Stephanie A.|last2=Price|first2=J. Jordan|date=2006|title=Water clarity and diving behavior in wintering common loons | jstor=4132565 | journal=Waterbirds | volume=29 | issue=2 | pages=169–175 | doi=10.1675/1524-4695(2006)29[169:wcadbi]2.0.co;2 |s2cid=86267739 }}</ref> For protection from [[Predation|predators]], common loons favour lakes with [[island]]s and [[cove]]s.<ref name=":2">{{cite web|url=https://www.allaboutbirds.org/guide/Common_Loon/id|title=All About Birds: Common Loon|publisher=Cornell Lab of Ornithology|archive-url=https://web.archive.org/web/20170525200226/https://www.allaboutbirds.org/guide/Common_Loon/lifehistory|archive-date=25 May 2017|access-date=6 August 2017}}</ref> They are rare visitors to the [[Arctic Ocean|Arctic]] coast.<ref>{{Cite book|title=Arctic National Wildlife Refuge: final comprehensive conservation plan, environmental impact statement, wilderness review, and wild river plans|date=1988|publisher=United States Fish and Wildlife Service, Region 7|page=450}}</ref> They are known to exhibit high breeding site fidelity.<ref name=":0">{{Cite journal|last1=Paruk|first1=James D|last2=Chickering|first2=Michael D.|last3=Long|first3=Darwin|last4=Uher-Koch|first4=Hannah |last5=East|first5=Andrew |last6=Poleschook|first6=Daniel|last7=Gumm|first7=Virginia|last8=Hanson|first8=William|last9=Adams|first9=Evan M.|date=2015|title=Winter site fidelity and winter movements in common loons (''Gavia immer'') across North America |journal=The Condor | volume=117|issue=4|pages=485–493|doi=10.1650/CONDOR-15-6.1 | doi-access=free }}</ref>
[[File:Gavia immer (Common Loon) Portrait-1APR2017.jpg|alt=Common Loon|thumb|In [[Bodega Bay, California]]]]
Some common loons remain in Iceland year-round, although most migrate. In North America, they winter mainly along north Atlantic and north-east Pacific coasts, many stopping off on the [[Great Lakes]] during their [[Bird migration|migration]].<ref name="hbw2" /> They migrate in the day, starting about two hours after sunrise and flying at altitudes of 1500 to 2700 m above sea level, above the convective and turbulent layer of air.<ref>{{cite journal|journal=The Condor| volume=84| pages=97–100| title=The migration of common loons through eastern New York| author=Kerlinger, Paul| year=1982 | url=https://sora.unm.edu/sites/default/files/journals/condor/v084n01/p0097-p0100.pdf|issue=1| doi=10.2307/1367828| jstor=1367828}}</ref> In winter they can be seen on North America coasts as far south as [[Baja California Peninsula|Baja California]], [[Sonora]], northern [[Sinaloa]], southern [[Texas]], and rarely northern [[Tamaulipas]].<ref>{{Cite book|title=Birds of Texas: A Field Guide|last1=Rappole|first1=John H|last2=Blacklock|first2=Gene W.| date=1994| location=College Station, TX | publisher=Texas A&M University Press| isbn=978-0-89096-545-0| page=14}}</ref><ref name=":3" /> In the east, several thousand winter along western European coasts, probably originating from Iceland, Greenland, and Canada.<ref name="hbw2" /> Their range extends into northwestern [[Europe]] from Finland to Portugal and southern and northwestern Spain ([[Galicia (Spain)|Galicia]] and [[Asturias]]), as well as the western [[Mediterranean Sea|Mediterranean]] off [[Catalonia]], and off Morocco in [[Africa]], although only a few hundred travel as far south as [[Iberian Peninsula|Iberia]].<ref name="iucn status 19 November 2021" /><ref name="hbw2" /><ref name=":3">{{Cite book|title=A Field Guide to Mexican Birds: Mexico, Guatemala, Belize, El Salvador|last1=Peterson|first1=Roger Tory|last2=Chalif|first2=Edward L.|date=1999|publisher=Houghton Mifflin Harcourt|isbn=978-0-395-97514-5|location=Boston, MA|page=[https://archive.org/details/fieldguidetomexi00edwa/page/3 3]|url=https://archive.org/details/fieldguidetomexi00edwa/page/3}}</ref> Although wintering site fidelity is not well known, annually, adults are observed to return to the same wintering locations in the Pacific Ocean ([[Morro Bay, California|Morro Bay]]), the Gulf of Mexico ([[Barataria Bay]]), the Atlantic Ocean ([[Maryland]] and [[Massachusetts]]), and the reservoir [[Lake Pateros]].<ref name=":0" />

They usually winter along coasts and on inland lakes, bays, inlets, and streams,<ref name=bwp /> with birds migrating to the nearest body of water that will not freeze over in the winter: western Canadian loons go to the [[Pacific Ocean|Pacific]], [[Great Lakes]] loons to the Gulf of Mexico region, eastern Canadian loons to the Atlantic, and some loons to large inland lakes and [[reservoir]]s.<ref name=":2" /> They appear in most of the inland waters of the United States. The [[South Carolina]] coast, the Gulf coast adjacent to the [[Florida Panhandle|Florida panhandle]], and the Atlantic seaboard from [[Massachusetts]] to [[Maine]] have some of the highest concentrations of common loons.<ref name=":102">{{Cite book|title=White River National Forest (N.F.), Land and Resource Management Plan: Environmental Impact Statement |last1=Garfield |first1=Eagle|last2=Mesa|first2=Gunnison|last3=Pitkin|first3=Moffat|last4=Routt|first4=Rio Blanco|last5=Colorado|first5=Summit Counties|publisher=United States Forest Service|year=2002|pages=62}}</ref> Occasional vagrants are recorded inland in Mexico, in [[San Luis Potosí]] and [[Coahuila]], as well as in [[Chiapas]] and [[Oaxaca]] in the south. They are accidental in northern Japan and the [[Commander Islands]] in northwestern Pacific, and Cuba in the [[West Indies]].<ref name="hbw2" />

== Behaviour ==
[[File:Common Loon (Gavia Immer).webm|thumb|Swimming]]
The common loon is an expert fisher, catching its prey underwater by diving as deep as {{convert|60|m|abbr=on}}.<ref name="Wisconsin Natural Resources">{{cite web|title=The Uncommon Loon|url=http://dnr.wi.gov/wnrmag/2013/02/loon.htm|publisher=Wisconsin Department of Natural Resources|access-date=2 June 2013}}</ref> With its large webbed feet, the common loon is an efficient underwater pursuit predator and adroit diver. It needs a long run-up distance to gain momentum for flight take-off and is ungainly on land, sliding on its belly and pushing itself forward with its legs. Its clumsiness on land is due to the legs being positioned at the rear of its body; the pelvic muscles are well developed,<ref>{{Cite journal|last=Wilcox|first=Harry Hammond|date=1952|title=The pelvic musculature of the loon, ''Gavia immer'' | jstor=2422198 | journal=The American Midland Naturalist|volume=48|issue=3|pages=513–573|doi=10.2307/2422198}}</ref> ideal for swimming but not well-suited for walking. When it lands on water, it skims along on its belly to slow down, rather than braking with its feet, as they are set too far back. The common loon swims and dives well, and flies competently for hundreds of kilometres in migration. It flies with its neck outstretched, usually calling a particular [[tremolo]] that can be used to identify a flying loon. Its flying speed is as much as {{convert|120|km/h|abbr=on}} during migration.<ref name="Wisconsin Natural Resources" /> Particularly during the breeding season, common loons frequently engage in territorial disputes against other water birds, including ducks and geese, and will attack or drive off competitors and intruders to their territory.<ref>{{Cite journal|last1=Kirkham|first1=Ian R.|last2=Johnson|first2=Stephen R.|date=1988|title=Interspecific Aggression in Loons (Agresión Interespecífica en Somormujos (Gavia spp.))|url=https://www.jstor.org/stable/4513284|journal=Journal of Field Ornithology|volume=59|issue=1|pages=3–6|jstor=4513284 |issn=0273-8570}}</ref><ref>{{Cite journal|last=Sperry|first=Mark L.|date=25 November 1986|title=Common Loon Attacks on Waterfowl|journal=Minnesota Department of Natural Resources Wetland Wildlife Populations and Research Group|pages=5}}</ref>

=== Feeding ===
[[File:093 - COMMON LOON (12-17-11) moss landing, ca (2) (8720312789).jpg|thumb|Foraging]]
Fish account for about 80% of the diet of the common loon. It forages on fish of up to {{convert|26|cm|abbr=on}} in length, including [[minnow]]s, [[Catostomidae|suckers]], [[Dorosoma|gizzard shad]], [[rock bass]], [[alewife (fish)|alewife]], [[northern pike]], [[Whitefish (fisheries term)|whitefish]], [[sauger]], [[brown bullhead]], [[pumpkinseed]], [[burbot]], [[walleye]], [[bluegill]], [[white crappie]], [[black crappie]], [[rainbow smelt]], and [[killifish]].<ref name=":8">{{Cite book|title=Birds of Ontario: Habitat Requirements, Limiting Factors, and Status: Volume 1–Nonpasserines: Loons through Cranes |last=Sandilands|first=Al|date=2011|publisher=University of British Columbia Press|isbn=978-0-7748-5943-1|location=Vancouver |page=171}}</ref> The young typically eat small minnows, and sometimes [[insect]]s and fragments of green vegetation.<ref name= MNFI/> The freshwater diet primarily consists of [[pike (fish)|pike]], [[perch]], [[Centrarchidae|sunfish]], [[trout]], and [[bass (fish)|bass]]; the saltwater diet primarily consists of [[Sebastes|rock fish]], [[flounder]], [[Brown trout|sea trout]], [[herring]], [[Sciaenidae|Atlantic croaker]], [[haddock]], and [[Atheriniformes|Gulf silverside]]. When there is either a lack of fish or they are difficult to catch, it preys on [[crustacean]]s, [[crayfish]], [[snail]]s, [[leech]]es, [[Larvae|insect larvae]], [[Mollusca|molluscs]], [[frog]]s, [[annelid]]s, and occasionally [[aquatic plant]] matter such as [[Potamogeton|pondweed]], roots, moss, [[Salix|willow shoots]], seeds, and [[algae]].<ref name="hbw2" /><ref name=":2" /><ref name=":9" /> It has also been known to eat ducklings.<ref name=":9" />

The common loon uses its powerful [[Hindlimb|hind legs]] to propel its body underwater at high speed to catch its prey, which it then swallows head-first. If the fish attempts to evade the common loon, the bird chases it down with excellent underwater manoeuvrability due to its strong legs.<ref name=":2" /> Most prey are swallowed underwater, where they are caught, but some larger prey are first brought to the surface. It is a visual predator, so it is essential to hunting success that the water is clear.<ref name= MNFI/> It normally dives {{Convert|4|to|10|m|abbr = on}}, but has been recorded to dive up to {{Convert|70|m|abbr = on}}.<ref name="hbw2" /> The average diving time is 42 seconds,<ref name="Wisconsin Natural Resources" /> but the maximum duration spent underwater is about {{Convert|1|minute||abbr = on}}.<ref name="hbw2"/>

===Breeding===
[[File:Gavia immer -Maine, USA -nest-8a (1).jpg|thumb|On a waterside nest in [[Maine]]]]
[[File:Eggs of British Birds Seebohm 1896 Plate21 The Common Loon.jpg|thumb|Egg]]
[[File:Milwaukee Public Museum March 2023 66 (Wisconsin Birds--Wisconsin Lake Country, Common Loon).jpg|thumb|Taxidermied common loon at the [[Milwaukee Public Museum]]]]
The common loon's mating system is serially [[Monogamy in animals|monogamous]]; breeding pairs jointly defend a territory consisting of an entire small lake or a protected bay within a large lake.<ref name=":11">{{Cite journal|last1=Piper|first1=Walter H.|last2=Brunk|first2=Kristin M.|last3=Flory|first3=Joel A.|last4=Meyer|first4=Michael W.|year=2017|title=The long shadow of senescence: age impacts survival and territory defense in loons|journal=Journal of Avian Biology|volume=48|issue=8|pages=1062–1070|doi=10.1111/jav.01393|url=https://digitalcommons.chapman.edu/cgi/viewcontent.cgi?article=1140&context=sees_articles|url-access=subscription}}</ref> A given male and female remain together throughout a breeding attempt, rear their own biological offspring,<ref>{{Cite journal|last1=Piper|first1=Walter H.|last2=Evers|first2=David C.|last3=Meyer|first3=Michael W.|last4=Tischler|first4=Keren B.|last5=Kaplan|first5=Joseph D.|last6=Fleischer|first6=Robert C.|date=1997|title=Genetic monogamy in the common loon (''Gavia immer'')|journal=Behavioral Ecology and Sociobiology|volume=41|issue=1|pages=25–31|doi=10.1007/s002650050360|bibcode=1997BEcoS..41...25P |s2cid=33036050}}</ref> 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.<ref>{{Cite journal|last1=Piper|first1=Walter H.|last2=Tischler|first2=Keren B.|last3=Klich|first3=Margaret|year=2000|title=Territory acquisition in loons: the importance of take-over|journal=Animal Behaviour|volume=59|issue=2|pages=385–394|doi=10.1006/anbe.1999.1295|pmid=10675261|s2cid=23085958}}</ref> 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.<ref>{{Cite journal|last1=Piper|first1=Walter H.|last2=Mager|first2=John N.|last3=Walcott|first3=Charles|last4=Furey|first4=Lyla|last5=Banfield|first5=Nathan|last6=Reinke|first6=Andrew|last7=Spilker|first7=Frank|last8=Flory|first8=Joel A.|date=2015|title=Territory settlement in common loons: no footholds but age and assessment are important|journal=Animal Behaviour|volume=104|pages=155–163|doi=10.1016/j.anbehav.2015.03.013|s2cid=53404673}}</ref><ref  name=piper2018>{{Cite journal|last1=Piper|first1=Walter H.|last2=Brunk|first2=Kristin M.|last3=Jukkala|first3=Gabriella L.|last4=Andrews|first4=Eric A.|last5=Yund|first5=Seth R.|last6=Gould|first6=Nelson G.|year=2018|title=Aging male loons make a terminal investment in territory defense|journal=Behavioral Ecology and Sociobiology|volume=72|issue=6|page=95 |doi=10.1007/s00265-018-2511-9|bibcode=2018BEcoS..72...95P |s2cid=46956208}}</ref>

Pairs do not remain together during winter;<ref name="hbw2" /><ref name="Evers2010" /> 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.<ref>{{Cite book|title=The Common Loon: Spirit of Northern Lakes|last=McIntyre|first=Judith|publisher=University of Minnesota Press|year=1988|isbn=978-0-8166-1651-0|location=Minneapolis, MN|page=[https://archive.org/details/commonloon00judi/page/9 9]|url=https://archive.org/details/commonloon00judi/page/9}}</ref> 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.<ref>{{Cite journal|last1=Sjölander|first1=Sverre|last2=Ågren|first2=Greta|date=1972|title=Reproductive behavior of the common loon|journal= Wilson Bulletin|volume=84|issue=3|pages=296–308|jstor=4160227| url=https://sora.unm.edu/sites/default/files/journals/wilson/v084n03/p0296-p0308.pdf }}</ref> The displays towards intruders, such as bow-jumping (an alternation of fencing and bill-dipping postures{{sfn|Johnsgard|1987|p=107}} 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"<ref>{{Cite journal | last1=Sjölander |first1=S.|last2=Ågren |first2=G.|date=1976|title=Reproductive behavior of the yellow-billed loon, ''Gavia adamsii''|url=https://sora.unm.edu/sites/default/files/journals/condor/v078n04/p0454-p0463.pdf|journal=The Condor| volume=78 | issue=4 | pages=454–463|doi=10.2307/1367094|jstor=1367094}}</ref>) are often misinterpreted as courtship.<ref name=":9">{{Cite book|title=The Eastman Guide to Birds: Natural History Accounts for 150 North American Species |last1=Eastman| first1=John|date=2000|publisher=Stackpole Books|isbn=978-0-8117-4552-9|location=Mechanicsburg, PA|page=219}}</ref>

Nesting typically begins in early May.{{sfn|Cramp|1977|p=61}} Significantly more nesting sites are found on islands than on mainland shoreline.<ref>{{Cite journal|last1=Radomski|first1=Paul J. |last2=Carlson|first2=Kristin|last3=Woizeschke|first3=Kevin|year=2014|title=Common loon (''Gavia immer'') nesting habitat models for north-central Minnesota lakes | journal=Waterbirds |volume=37|issue=sp1|pages=102–117|doi=10.1675/063.037.sp113|doi-access=free}}</ref> Breeding pairs patrol their territories routinely, even at night,<ref>{{cite journal|author=Paruk, James D.|year=2008|title=Nocturnal behaviour of the common loon, Gavia immer|journal=Canadian Field-Naturalist|volume=122|pages=70–72|doi=10.22621/cfn.v122i1.548|doi-access=free}}</ref> defending the territory both physically and vocally.<ref>{{Cite web|url=http://animaldiversity.org/accounts/Gavia_immer/|title=''Gavia immer'' (common loon)|last=Rodriguez|first=R.|date=2002|website=Animal Diversity Web|archive-url=https://web.archive.org/web/20170714185921/http://animaldiversity.org/accounts/Gavia_immer/|archive-date=14 July 2017|access-date=14 July 2017}}</ref> 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.<ref name=":12">{{Cite journal|last1=Piper|first1=Walter H.|last2=Walcott|first2=Charles|last3=Mager|first3=John N.|last4=Spilker|first4=Frank J.|year=2008|title=Nestsite selection by male loons leads to sex-biased site familiarity|journal=Journal of Animal Ecology|volume=77|issue=2|pages=205–210|doi=10.1111/j.1365-2656.2007.01334.x|pmid=17976165|doi-access=free|bibcode=2008JAnEc..77..205P }}</ref> 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.<ref name=":12" /> Despite the lead role of males in nest site selection, both sexes contribute substantially to [[nest]] construction.<ref name=":2" /> The nest is about {{Convert|56|cm|abbr=on}} wide and is constructed out of dead [[Hymenachne|marsh grasses]] and other indigenous plants, and formed into a mound along the vegetated coasts of lakes greater than {{convert|3.7|ha|abbr=on}}.<ref name=":72" /><ref name=":2" /> After a week of construction in late spring, one parent climbs on top to mould the interior of the nest to the shape of its body.<ref name=":2" /> Based on a number of studies, nesting success averages about 40%, and most newly hatched young survive due to parental care.<ref name=":13">{{Cite book|title=Birds of Lake, Pond, and Marsh: Water and Wetland Birds of Eastern North America|last=Eastman|first=John Andrew| year=1999 |location=Mechanicsburg, PA | publisher=Stackpole Books |isbn=978-0-8117-2681-8|page=216}}</ref>

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.<ref name=":2" /> A clutch consists of two (occasionally one) olive-brown oval [[egg]]s with dark brown spots.<ref name=":72" /> Incubation is carried out jointly by male and female and lasts about 28 days.<ref name=Evers2010/><ref name="MNFI" /> Loons often place nests along steep lake shorelines where adults can quickly dive underwater when approached by predators.<ref name=":1">{{Cite journal|last=McIntyre|first=Judith W.|date=1983|title=Nurseries: a consideration of habitat requirements during the early chick-rearing period in common loons|jstor=4512827|journal=Journal of Field Ornithology|volume=54|issue=3| pages=247–253}}</ref> The eggs are about {{Convert|88|mm|abbr = on}} long and {{Convert|55|mm|abbr = on}} wide<ref name=":2" /> and the two eggs are laid with an interval of one to three days between them,<ref name=":8" /> and hatch [[wikt:asynchronous|asynchronously]].<ref name=":13" />

Newly hatched chicks are dark chocolate brown in colour 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.<ref name=":2" /> 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.<ref name=":1" /><ref name="Jukkala 2015 551–558">{{Cite journal|last1=Jukkala|first1=Gabriella|last2=Piper|first2=Walter|year=2015|title=Common loon parents defend chicks according to both value and vulnerability|journal=Journal of Avian Biology|volume=46|issue=6|pages=551–558|doi=10.1111/jav.00648}}</ref> Male parents defend broods consisting of two chicks more vigorously than singleton chicks, chiefly with the territorial yodel call.<ref name="Jukkala 2015 551–558"/> The chicks are capable of making shallow dives from their first day<ref name=":7">{{Cite journal|last=Barr|first=J.F.|year=1996|title=Aspects of common loon (''Gavia immer'') feeding biology on its breeding ground| journal=Hydrobiologia |volume=321|issue=2|pages=119–144|doi=10.1007/bf00023169|s2cid=32804759}}</ref> but make deeper dives as they grow.<ref name="Evers2010">{{cite journal|url=https://birdsna.org/Species-Account/bna/species/comloo|title=Common Loon (''Gavia immer'') | last1=Evers|first1=D.C. | last2=Paruk | first2=J.D. | year=2021 |editor-last=Poole |editor-first=A.F. |journal=The Birds of North America | publisher=Cornell Lab of Ornithology |url-access=subscription | last3=McIntyre | first3=J.W. | last4=Barr | first4=J.F. |doi=10.2173/bow.comloo.02 }}</ref> [[Fledge|Fledging]] takes 70 to 77 days.<ref name="hbw2" /> Usually, only one brood is raised.<ref name=":2" /> Both parents feed the chicks live prey from hatching to fledging. As they grow, chicks are able to catch an increasingly large proportion of their diet by themselves; they can feed and fend for themselves after about two months, although many juveniles continue to beg from adults well beyond this age. The parent birds capture small fish and hold them crosswise in their bill, call and approach the chicks with their head lowered so that the chicks can grasp them.<ref name=":7" /> If food is scarce, the larger chick may peck its small sibling incessantly; on small lakes with limited food, only one chick often survives.<ref name=":14">{{Cite journal|last1=Piper|first1=Walter H.|last2=Grear|first2=Jason S.|last3=Meyer|first3=Michael W.|year=2012|title=Juvenile survival in common loons ''Gavia immer'': effects of natal lake size and pH |journal=Journal of Avian Biology |volume=43|issue=3|pages=280–288|doi=10.1111/j.1600-048x.2012.05633.x}}</ref> Juveniles leave the breeding ground before ice formation in the fall, weeks after their parents.<ref name=":72" /> A pair of loons raising two chicks have been estimated to feed on {{convert|423|kg}} of fish during the five and a half months that they spend in their breeding territory.<ref name=":7" />

=== Habitat selection ===
Loons exhibit a strong tendency to settle as breeders on a lake that resembles their natal one, a phenomenon termed natal habitat imprinting. This preference is based on two lake attributes: size and pH.<ref name=":15">{{Cite journal|last1=Piper|first1=Walter H.|last2=Palmer|first2=Michael W.|last3=Banfield|first3=Nathan|last4=Meyer|first4=Michael W.|date=2013|title=Can settlement in natal-like habitat explain maladaptive habitat selection? |journal=Proceedings of the Royal Society of London B: Biological Sciences|volume=280|issue=1765|pages=20130979|doi=10.1098/rspb.2013.0979 |pmid=23804619|pmc=3712445}}</ref> The behaviour is puzzling, because it is as strong in loons hatched on small, acidic lakes as those from large lakes of neutral pH. Hence, the former group is exhibiting active preference for lakes that have been shown to result in higher chick mortality and lower breeding success.<ref name=":14" /><ref name=":15" />

===Vocalizations===

The common loon produces a variety of vocalizations, the most common of which are the tremolo, the yodel, the wail, and the hoot. Each of these calls communicates a distinct message. The frequency at which it vocalizes has been shown to vary based on time of day, weather, and season. It is most vocally active between mid-May and mid-June. The wail, yodel, and tremolo calls are sounded more frequently at night than during the day; calls have also been shown to occur more frequently in cold temperatures and when there is little to no rain.<ref name="Mennill2014" />

{{Listen|filename=Common loon tremolo.ogg|pos=right|title=Common loon tremolo call}}
The tremolo call—sometimes called the "laughing" call—is characterized by its short, wavering quality. It often uses this call to signal distress or alarm caused by territorial disputes or perceived threats.<ref name="Mennill2014">{{cite journal|last1=Mennill|first1=Daniel J.|date=2014|title=Variation in the vocal behavior of common loons (''Gavia immer''): Insights from landscape-level recordings|journal=Waterbirds|volume=37|issue=sp1|pages=26–36|doi=10.1675/063.037.sp105 | doi-access=free }}</ref> It emits a tremulous series of up to 10 rather high notes ''(hu)-heheheheheheha''.<ref name="hbw2"/> It also uses the tremolo to communicate its presence to other loons when they arrive at a lake, often when they are flying overhead. It is the only vocalization used in flight.<ref name="vtfishandwildlife">{{cite web|url=http://www.vtfishandwildlife.com/get_the_lead_out_looncall.cfm|title=Loon Vocalizations: What are you hearing and what does it mean?|publisher=Vermont Fish and Wildlife|archive-url=https://web.archive.org/web/20140913011626/http://www.vtfishandwildlife.com/get_the_lead_out_looncall.cfm|archive-date=13 September 2014|access-date=27 August 2017}}</ref> The tremolo call has varying three levels of intensities that correlate with a loon's level of distress, and the types are differentiated by increasingly higher pitch frequencies added to the call.<ref name="Barklow">{{cite journal|last1=Barklow|first1=William E.|year=1979|title=Graded frequency variations of the tremolo call of the common loon (''Gavia immer'')|journal=The Condor|volume=81|issue=1|pages=53–64| url=https://sora.unm.edu/sites/default/files/journals/condor/v081n01/p0053-p0064.pdf | doi=10.2307/1367857|jstor=1367857}}</ref>

{{Listen|filename=Loon yodel.ogg|pos=right|title=Male Common loon yodel call}}
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.<ref name="Mager2012">{{cite journal|last1=Mager III|first1=John N|last2=Walcott|first2=Charles|last3=Piper|first3=Walter H|date=2012|title=Male common loons signal greater aggressive motivation by lengthening territorial yodels|url=https://www.researchgate.net/publication/257920946 |journal=Wilson Journal of Ornithology|volume=124|issue=1|pages=73–80|doi=10.1676/11-024.1|s2cid=85216811}}</ref> The dominant frequencies in the yodel indicate the body mass and thereby the health of males.<ref>{{Cite journal|last1=Mager|first1=John N.|last2=Walcott|first2=Charles|last3=Piper|first3=Walter H.|title=Male common loons, ''Gavia immer'', communicate body mass and condition through dominant frequencies of territorial yodels |journal=Animal Behaviour|volume=73|issue=4|pages=683–690|doi=10.1016/j.anbehav.2006.10.009|citeseerx=10.1.1.483.1889|year=2007|s2cid=43610342}}</ref> A male that occupies a new territory appears to alter its yodel to be clearly distinguishable from the call of the previous territory owner.<ref>{{Cite journal|last1=Walcott|first1=Charles|last2=Mager|first2=John N.|last3=Piper|first3=Walter|date=2006|title=Changing territories, changing tunes: male loons, ''Gavia immer'', change their vocalizations when they change territories|url=https://www.fws.gov/uploadedFiles/Walcott2005.pdf|journal=Animal Behaviour|volume=71|issue=3|pages=673(11)|doi=10.1016/j.anbehav.2005.07.011|s2cid=43750841}}</ref>

A loon's wail is a long call consisting of up to three notes, and is often compared to a [[wolf]]'s [[Howling|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.<ref name="vtfishandwildlife" /> It is a loud ''aaoo'', ''weee-wea weee-wea weee-wea'', or ''ooo-aaah-éééé''.<ref name="hbw2"/>

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.<ref name="Mennill2014" /> 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.<ref name="vtfishandwildlife" />

== 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.<ref>{{Cite book|title=A replicable capture method for adult and juvenile common loons on their nesting lakes. In: 1992 Conference on the Loon and Its Ecosystem|last=Evers|first=David|publisher=North American Loon Fund|year=1993|location=Meredith, NH, USA}}</ref> 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,<ref name=":11" /> 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.<ref name=piper2018/> 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.<ref name=piper2018/>

== Predators and parasites ==

Adult common loons have few predators, although [[bald eagle]]s will attack incubating birds. Attacks by sharks in winter have also been recorded.<ref name="Evers2010" /> 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.<ref>{{Cite journal|journal=Bird Observer|issue = 3 |year=2004|volume = 32|last1= Davies |first1=William E. |pages=202–204|url=http://www.birdobserver.org/Portals/0/PDF_open/bo32-3-web.pdf?ver=2017-02-10-105735-433#view=Fit| title=About the cover. Common loon}}</ref>

Eggs are taken by a number of mammals, including [[American mink]], [[striped skunk]], [[North American river otter|otters]], foxes and [[raccoon]]s, with the latter being responsible for nearly 40% of all nest failures. Birds such as [[herring gull]]s, [[northern raven]]s and [[American crow]]s will eat unattended eggs. Because their nests are at the water's edge, common loon eggs are especially vulnerable if the adult is absent.<ref name="Evers2010" />

Chicks may be killed by [[common snapping turtle]]s, large gulls, bald eagles and large fish such as [[northern pike]] and [[largemouth bass]]. The eagle in particular is a significant predator of chicks.<ref name="Evers2010" />

Internal parasites of the common loon include many species of [[helminths|worms]], including [[trematoda|flatworms]], [[cestoda|tapeworms]], [[nematode]]s and [[acanthocephala|spiny-headed worms]].<ref>{{Cite journal|last1=Daoust|first1=Pierre-Yves|last2=Conboy|first2=Gary|last3=McBurney|first3=Scott|last4=Burgess|first4=Neil|year=1998|title=Interactive mortality factors in common loons from maritime Canada|journal=Journal of Wildlife Diseases|volume=34|issue=3|pages=524–531|doi=10.7589/0090-3558-34.3.524|pmid=9706561|s2cid=24447180}}</ref> High levels of worms may result from feeding changes due to low availability of fish, and can lead to illness and death.<ref name= kinsella>{{cite journal | last1=Klnsella | first1=J.M. | last2=Forrester | first2=Donald J. | title=Parasitic helminths of the common loon, ''Gavia immer'', on its wintering grounds in Florida | journal=Journal of the Helminthological Society of Washington | volume =66 | issue=1 | pages=1–6 | year=1999 | url=http://bionames.org/bionames-archive/issn/1049-233X/66/1.pdf }}</ref> Protozoal infections including one caused by ''Eimeria gaviae''<ref>{{Cite journal|last1=Montgomery|first1=Roy D.|last2=Novilla|first2=Meliton N.|last3=Shillinger|first3=Robert B.|date=1978|title=Renal coccidiosis caused by ''Eimeria gaviae'' n. sp. in a common loon (''Gavia immer'') | jstor=1589663 |journal=Avian Diseases|volume=22|issue=4|pages=809–814|doi=10.2307/1589663|pmid=749899}}</ref> and [[avian malaria]] have been recorded in this loon.<ref>{{cite journal|last1=Martinsen|first1=Ellen S. |last2=Sidor|first2=Inga F. | last3=Flint | first3=Sean | last4=Cooley | first4=John | last5=Pokras | first5=Mark A. |year=2017 | title=Documentation of malaria parasite (''Plasmodium'' spp.) infection and associated mortality in a common loon (''Gavia immer'') | journal=Journal of Wildlife Diseases | volume=53 | issue=4 | pages=859–863 | doi=10.7589/2016-08-195 |pmid=28665230 |s2cid=4391165 }}</ref> The [[black fly]] ''[[Simulium|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.<ref name="wein">{{cite journal|last1=Weinandt|first1=Meggin L. |last2=Meyer|first2=Michael|last3=Strand|first3=Mac|last4=Lindsay|first4=Alec R.|year=2012|title=Cues used by the black fly,''Simulium annulus'', for attraction to the common loon (''Gavia immer'')|url=http://commons.nmu.edu/cgi/viewcontent.cgi?article=1010&context=facwork|journal=Journal of Vector Ecology |volume=37|issue=2|pages=359–364|doi=10.1111/j.1948-7134.2012.00239.x|pmid=23181860 |s2cid=768681 |doi-access=free|url-access=subscription}}</ref><ref>{{Cite journal|last1=Piper|first1=Walter H.|last2=Tischler|first2=Keren B.|last3=Reinke|first3=Andrew|year=2018|title=Common loons respond adaptively to a black fly that reduces nesting success|journal=The Auk|volume=135|issue=3|pages=788–797|doi=10.1642/auk-17-239.1|s2cid=90934731|url=https://digitalcommons.chapman.edu/cgi/viewcontent.cgi?article=1202&context=sees_articles|doi-access=free}}</ref> External parasites include [[ischnocera]]n [[bird louse|feather lice]], although these are not found on the bird's head.<ref name=Rothschild>{{cite book |last1=Rothschild |first1=Miriam |author-link1=Miriam Rothschild |last2=Clay |first2=Theresa |title=Fleas, Flukes and Cuckoos. A Study of Bird Parasites |year=1953 |publisher=Collins |location=London |page =[https://archive.org/details/fleasflukescucko00roth/page/153 153] |url=https://archive.org/details/fleasflukescucko00roth}}</ref>

[[Botulism]], acquired by eating infected fish, can lead to paralysis and drowning. [[Aspergillosis]] is another cause of emaciation and death.<ref>{{cite book|chapter=Causes of mortality in common loons|last1=Franson | first1=J.C.| last2=Cliplef | first2=David J. |title=Proceedings from the 1992 Conference on the Loon and its Ecosystem: Status, management, and environmental concerns|pages=2–12|year=1992|publisher=US Fish and Wildlife Service}}</ref> Outbreaks sometimes lead to thousands of deaths.<ref name= MNFI>{{cite web |last1= Gibson|first1= J.W. |title = ''Gavia immer'' Brünnich Common Loon| work=Michigan Natural Features Inventory |year=2007| pages=1–6| publisher=Michigan State University |url= https://mnfi.anr.msu.edu/abstracts/zoology/Gavia_immer.pdf }}</ref>

==Status and conservation==
Since 1998, the common loon has been rated as a species of [[Least-concern species|least concern]] on the [[IUCN Red List of Endangered Species]]. This is because it has a large range – more than {{convert|20000|km2|abbr=on}} – and because it has a stable population trend that does not warrant a [[Vulnerable species|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.<ref name="iucn status 19 November 2021" /> 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.<ref name="Evers2010" />

The common loon is listed under Appendix II of the [[Convention on the Conservation of Migratory Species of Wild Animals|Convention on the Conservation of Migratory Species]], and in Article I under the European Union (EU) [[Birds Directive]].<ref name="iucn status 19 November 2021" /> It is one of the species to which the [[Agreement on the Conservation of African-Eurasian Migratory Waterbirds]] (AEWA) is applied.<ref>{{Cite web|url=http://www.unep-aewa.org/en/species/gavia-immer|title=''Gavia immer'' {{!}} AEWA|archive-url=https://web.archive.org/web/20160816145045/http://www.unep-aewa.org/en/species/gavia-immer|archive-date=16 August 2016|access-date=12 July 2017}}</ref> In Europe it appears in 20 Important Bird Areas ([[Important Bird Area|IBAs]]), including Ireland, Svalbard, mainland Norway, Iceland, Spain, and the United Kingdom. It is also a listed species in 83 [[Special Protection Area]]s in the EU [[Natura 2000]] network.<ref name="iucn status 19 November 2021" /> The [[United States Forest Service|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 National Forests|Huron-Manistee]], [[Ottawa National Forest|Ottawa]], and [[Hiawatha National Forest|Hiawatha]] national forests as a regional forester sensitive species.<ref name=":4">{{Cite journal|last=Tischler|first=Keren B.|date=2011|title=Species Conservation Assessment for the Common Loon (''Gavia immer'') in the upper Great Lakes|url=https://www.fws.gov/uploadedFiles/tischler_common_loon_2011.pdf|journal=USDA Forest Service, Eastern Region|pages=1–59}}</ref>

=== Threats to status and conservation ===

==== Effects of mercury and acid rain pollution on health and brood productivity ====
The common loon is a key indicator of [[Mercury (element)|mercury]] deposition in aquatic environments due to its position at the top of the [[food chain]].<ref name=":10">{{Cite journal |last1=Evers |first1=David C. |last2=Savoy |first2=Lucas J. |last3=DeSorbo |first3=Christopher R. |last4=Yates |first4=David E. |last5=Hanson |first5=William |last6=Taylor |first6=Kate M. |last7=Siegel |first7=Lori S. |last8=Cooley |first8=John H. |last9=Bank |first9=Michael S. |last10=Major |first10=Andrew |last11=Munney |first11=Kenneth |date=2008-02-01 |title=Adverse effects from environmental mercury loads on breeding common loons |url=https://doi.org/10.1007/s10646-007-0168-7 |journal=Ecotoxicology |language=en |volume=17 |issue=2 |pages=69–81 |doi=10.1007/s10646-007-0168-7 |pmid=17909967 |bibcode=2008Ecotx..17...69E |s2cid=17769869 |issn=1573-3017|url-access=subscription }}</ref> The main contributors to elevated mercury concentrations in aquatic environments are coal burning power plants, waste incineration, and metal production.<ref name=":19">{{Cite web |title=Threats to Loons |url=https://www.adkloon.org/threats-to-loons |access-date=2022-03-07 |website=Adirondack Center for Loon Conservation |language=en-US}}</ref> Although environmental mercury (Hg) is naturally occurring, [[methylmercury]] ({{chem2|CH3Hg+}}, sometimes written as {{chem2|MeHg+}}) is a biologically toxic form that accumulates throughout aquatic environments in the northeastern United States.<ref name=":20">{{Cite journal |last1=Schoch |first1=Nina |last2=Glennon |first2=Michale J. |last3=Evers |first3=David C. |last4=Duron |first4=Melissa |last5=Jackson |first5=Allyson K. |last6=Driscoll |first6=Charles T. |last7=Ozard |first7=John W. |last8=Sauer |first8=Amy K. |date=April 2014 |title=The Impact of Mercury Exposure on the Common Loon (Gavia immer) Population in the Adirondack Park, New York, USA |url=https://bioone.org/journals/waterbirds/volume-37/issue-sp1/063.037.sp116/The-Impact-of-Mercury-Exposure-on-the-Common-Loon-Gavia/10.1675/063.037.sp116.full |journal=Waterbirds |volume=37 |issue=sp1 |pages=133–146 |doi=10.1675/063.037.sp116 |s2cid=85674745 |issn=1524-4695|url-access=subscription }}</ref> Methylmercury, a [[neurotoxin]], has been shown to have a wide range of behavioral, reproductive, and survival effects on the common loon.<ref name=":21">{{Cite journal |last=Schoch |first=Nina |date=2006-01-01 |title=The Adirondack Cooperative Loon Program: Loon Conservation in the Adirondack Park |url=https://digitalworks.union.edu/ajes/vol13/iss2/5 |journal=Adirondack Journal of Environmental Studies |volume=13 |issue=2 |issn=1075-0436}}</ref> Previous research has found a correlation between mercury levels and [[pH]], with more acidic aquatic environments being at the highest risk for elevated methylmercury concentrations.<ref name=":22">{{Cite journal |last1=Yu |first1=Xue |last2=Driscoll |first2=Charles T. |last3=Montesdeoca |first3=Mario |last4=Evers |first4=David |last5=Duron |first5=Melissa |last6=Williams |first6=Kate |last7=Schoch |first7=Nina |last8=Kamman |first8=Neil C. |date=2011-10-01 |title=Spatial patterns of mercury in biota of Adirondack, New York lakes |url=https://doi.org/10.1007/s10646-011-0717-y |journal=Ecotoxicology |language=en |volume=20 |issue=7 |pages=1543–1554 |doi=10.1007/s10646-011-0717-y |issn=1573-3017 |pmc=3175042 |pmid=21691858|bibcode=2011Ecotx..20.1543Y }}</ref> Once mercury enters the water, it is taken up by fish and spread throughout the food chain.<ref name=":19" /> 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 local aquatic pH.<ref name=":16">{{Cite journal |last1=Champoux |first1=L. |last2=Masse |first2=D. C. |last3=Evers |first3=D. |last4=Lane |first4=O. P. |last5=Plante |first5=M. |last6=Timmermans |first6=S. T. A. |date=September 2006 |title=Assessment of mercury exposure and potential effects on common loons (Gavia immer) in Québec |url=http://link.springer.com/10.1007/s10750-006-0066-7 |journal=Hydrobiologia |language=en |volume=567 |issue=1 |pages=263–274 |doi=10.1007/s10750-006-0066-7 |issn=0018-8158 |s2cid=10621451|url-access=subscription }}</ref> 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.<ref name=":6">{{Cite journal |last1=Bianchini |first1=Kristin |last2=Tozer |first2=Douglas C. |last3=Alvo |first3=Robert |last4=Bhavsar |first4=Satyendra P. |last5=Mallory |first5=Mark L. |date=October 2020 |title=Drivers of declines in common loon (Gavia immer) productivity in Ontario, Canada |url=https://linkinghub.elsevier.com/retrieve/pii/S0048969720332447 |journal=Science of the Total Environment |language=en |volume=738 |pages=139724 |bibcode=2020ScTEn.73839724B |doi=10.1016/j.scitotenv.2020.139724 |pmid=32531589|s2cid=219620784 |url-access=subscription }}</ref> 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.<ref name=":6" />

Although the common loon is able to decrease their methylmercury levels by molting and laying eggs, continued consumption of fish with raised methylmercury levels prevents these mechanisms from effectively lowering methylmercury levels.<ref name=":21"/> Mercury concentrations have been shown to vary by the 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.<ref name=":17">{{Cite journal|last1=Schoch|first1=Nina|last2=Glennon|first2=Michale J.|last3=Evers|first3=David C.|last4=Duron|first4=Melissa|last5=Jackson|first5=Allyson K.|last6=Driscoll|first6=Charles T.|last7=Ozard|first7=John W.|last8=Sauer|first8=Amy K.|date=April 2014|title=The Impact of Mercury Exposure on the Common Loon ( Gavia immer ) Population in the Adirondack Park, New York, USA|url=http://www.bioone.org/doi/abs/10.1675/063.037.sp116|journal=Waterbirds|language=en|volume=37|issue=sp1|pages=133–146|doi=10.1675/063.037.sp116|s2cid=85674745|issn=1524-4695|url-access=subscription}}</ref> 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.<ref name=":16" /> Juveniles had the lowest blood mercury concentration.<ref name=":18">{{Cite journal|last1=Burgess|first1=Neil M.|last2=Meyer|first2=Michael W.|date=February 2008|title=Methylmercury exposure associated with reduced productivity in common loons|url=http://link.springer.com/10.1007/s10646-007-0167-8|journal=Ecotoxicology|language=en|volume=17|issue=2|pages=83–91|doi=10.1007/s10646-007-0167-8|pmid=18038272|bibcode=2008Ecotx..17...83B |s2cid=40571426|issn=0963-9292|url-access=subscription}}</ref> Scientists found that the data from juveniles helped to best indicate the local mercury availability as they are fed exclusively from their natal territory.<ref name=":16" />

Elevated levels of mercury have been associated with changes in foraging and [[brooding]] behavior among adult common loons, especially in higher concentrations.<ref name=":18" /> Studies have found that elevated levels of methylmercury are associated with lethargy and decreased time spent foraging in adult common loons.<ref name=":10" /> A different study carried out in the [[Adirondack Mountains]] found that elevated levels of methylmercury are associated with reduced diving frequency in adult common loons.<ref>{{Cite journal |last=Stewart |first=Paul A. |date=January 1967 |title=Diving Schedules of a Common Loon and a Group of Oldsquaws |journal=The Auk |volume=84 |issue=1 |pages=122–123 |doi=10.2307/4083265 |jstor=4083265 |issn=0004-8038|doi-access=free }}</ref> One 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.<ref name=":18" /> 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.<ref name=":6" /> An association has also been observed between elevated blood methylmercury levels and aberrant incubation patterns.<ref name=":10" /> Adult common loons with high levels of methylmercury were found to spend less time incubating and in the nest, increasing the risks of [[predation]] and the eggs overheating/overcooling.<ref name=":10" /> Together, the effects of heightened methylmercury levels on parenting behaviors may contribute to lower chick survival rates. One study in Maine and New Hampshire found that high levels of methylmercury in parents are associated with a significant decrease in the number of fledged young, with common loons in the highest risk group producing 41% fewer fledged young than common loons with low levels of methylmercury.<ref name=":10" />

==== Mercury deposition in the Adirondack Mountains ====
The common loons of the [[Adirondack Mountains]] are particularly affected by methylmercury as the acidity of the lakes provides an environment conducive to converting environmental mercury to methylmercury.<ref name=":20" /> One study found that 21% of the male Adirondack common loon and 8% of the female Adirondacks common loon sampled were at high risk for detrimental impacts such as behavioral and reproductive abnormalities.<ref name=":20" /> In the Adirondacks, [[bioaccumulation]] factors for methylmercury were found to increase up the food chain, leaving common loons at the highest risk for detrimental effects from methylmercury.<ref name=":20" /> [[Spatial analysis]] indicates that the highest aquatic mercury concentrations are found in the southwestern portion of the Adirondacks, an area with lakes heavily affected by acid rain.<ref name=":22" /> Organizations such as the Adirondack Loon Center and the Adirondack Cooperative Loon Program spearhead loon conservation efforts in the Adirondacks by performing research, engaging the public, and informing public policy.<ref name=":21" />

==== Breeding range decline ====
The common loon's breeding range has moved northward, the species breeding as far south as Iowa a century ago.<ref name=":5">{{Cite web|url=http://seagrant.wisc.edu/birds/Common_Loon_conservation.html|title=Common Loon Conservation Status- Migratory Birds of the Great Lakes – University of Wisconsin Sea Grant Institute|last=Wiland|first=L.|date=2007 |archive-url=https://web.archive.org/web/20170712112025/http://seagrant.wisc.edu/birds/Common_Loon_conservation.html|archive-date=12 July 2017|access-date=12 July 2017}}</ref> 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<ref>{{Cite journal | last1=Franson | first1=J. Christian | last2=Hansen | first2=Scott P. | last3=Pokras | first3=Mark A. | last4=Miconi | first4=Rose | date=2001 | title=Size characteristics of stones ingested by common loons | jstor=1369696 | journal=The Condor | volume=103 | issue=1 | pages=189–191 | doi=10.1650/0010-5422(2001)103[0189:scosib]2.0.co;2| s2cid=86704804 | doi-access=free }}</ref>) and mercury contamination from industrial waste.<ref name="locke">{{cite journal | last1=Locke | first1=L.N. | last2=Kerr | first2=S.M.| last3=Zoromski | first3=D. | title=Lead poisoning in common loons (''Gavia immer'') | journal=Avian Diseases | volume=26| issue=2 | pages=392–396 | year=1982 | doi= 10.2307/1590110 | jstor=1590110 | pmid=7103895 | citeseerx=10.1.1.514.3406 }}</ref> Heavy metals such as mercury may be partially removed through biological processes such as excretion or deposition in feathers, but their adverse effects are [[biomagnification|magnified]] through concentration of the toxic elements in organs such as the liver. Eggs shells may also contain metal contaminants,<ref name="burger">{{cite journal | last1=Burger | first1=Joanna | last2=Pokras | first2=Mark | last3=Chafel | first3=Rebecca | last4=Gochfeld | first4=Michael | title=Heavy metal concentrations in feathers of common loons (''Gavia immer'') in the northeastern United States and age differences in mercury levels | journal=Environmental Monitoring and Assessment | volume=30 | issue=1| pages=1–7 | year =1994 | doi=10.1007/BF00546196 | pmid=24213705 | bibcode=1994EMnAs..30....1B | s2cid=24178181 }}</ref> leading to low reproductive productivity. High levels of heavy metals are linked to loons being in poor condition,<ref name="Scheuhammer">{{cite journal | last1=Scheuhammer | first1=Anton M. | last2=Wong | first2=Allan H.K. | last3=Bond | first3=Della | title=Mercury and selenium accumulation in common loons (''Gavia immer'') and common mergansers (''Mergus merganser'') from Eastern Canada | journal=Environmental Toxicology and Chemistry | volume=17 | issue=2 | pages=197–201| year=1998 | doi=10.1002/etc.5620170209 | s2cid=85336567 }}</ref> males being affected more because they eat larger fish.<ref name="MNFI" />

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.<ref>{{Cite journal|last1=Desorbo|first1=Christopher R|last2=Taylor|first2=Kate M.|last3=Kramar|first3=David E. | last4=Fair | first4=Jeff | last5=Cooley | first5=John H. | last6=Evers | first6=David C. | last7=Hanson | first7=William | last8=Vogel | first8=Harry S. | last9=Atwood | first9=Jonathan L. |date=2007 | title=Reproductive advantages for common loons using rafts | journal=Journal of Wildlife Management | volume=71 | issue=4 | pages=1206–1213 | doi=10.2193/2006-422|bibcode=2007JWMan..71.1206D |s2cid=85992979|issn=0022-541X }}</ref> 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.<ref>{{Cite journal|last1=McIntyre|first1=Judith W. | last2=Mathisen | first2=John E. | date=1977 | title=Artificial islands as nest sites for common loons | journal=The Journal of Wildlife Management | volume=41 | issue=2 | pages=317–319 | doi=10.2307/3800613 | jstor=3800613 }}</ref> 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.<ref name=":5" /> It is still considered an "injured" species in Alaska as a result of the [[Exxon Valdez oil spill]].<ref name=":4" />

=== Lead poisoning ===
In a 2003 survey of [[New England]] dead loons, lead poisoning from fishing weights accounted for about half of the deaths, and other human factors directly caused the death of 52% of the observed 522 loons.<ref>{{Cite journal |last1=Sidor |first1=Inga F. |last2=Pokras |first2=Mark A. |last3=Major |first3=Andrew R. |last4=Poppenga |first4=Robert H. |last5=Taylor |first5=Kate M. |last6=Miconi |first6=Rose M. |date=April 2003 |title=Mortality of Common Loons in New England, 1987 to 2000 |journal=Journal of Wildlife Diseases |volume=39 |issue=2 |pages=306–315 |doi=10.7589/0090-3558-39.2.306 |issn=0090-3558|doi-access=free |pmid=12910757 }}</ref>

==In culture==
[[File:Cassell's book of birds (Plate XXXIX) (8574783618).jpg|thumb|''Cassell's book of birds'', ca 1875]]

The common loon appears on Canadian currency, including the [[Loonie|one-dollar "loonie"]] coin and the previous series of [[Canadian twenty-dollar note|$20 bills]].<ref>{{Cite book|last1=Grzimek|first1=Bernhard|title=Grzimek's Animal Life Encyclopedia, Volume 8: Birds I|last2=Schlager|first2=Neil|date=2003|publisher=Gale|isbn=978-0-7876-6571-5|page=161}}</ref> It is the [[List of Canadian provincial and territorial symbols|provincial bird]] of [[Ontario]].<ref>{{Cite book|last=Townsley|first=Frank|title=British Columbia: Graced by Nature's Palette|date=2016|publisher=FriesenPress|isbn=978-1-4602-7773-7|page=191}}</ref> It was designated the [[List of U.S. state birds|state bird]] of the U.S. state of [[Minnesota]] in 1961,<ref>{{Cite book|last=Carlson|first=Bruce M|title=Beneath the Surface: A Natural History of a Fisherman's Lake|date=2007|publisher=Minnesota Historical Society|isbn=978-0-87351-578-8|page=159}}</ref> and also appears on the Minnesota [[State Quarter]].<ref>{{Cite book|last=Noles|first=Jim|title=A Pocketful of History: Four Hundred Years of America—One State Quarter at a Time|date=2009|publisher=Da Capo Press|isbn=978-0-7867-3197-8}}</ref>

=== Folklore ===
The voice and appearance of the common loon has made it prominent in several [[Indigenous peoples of the Americas|Native American]] tales. These include an [[Ojibwe]] story of a loon that created the world,<ref>{{Cite book|title=The Common Loon: Population Status and Fall Migration in Minnesota|last1=Svingen|first1=Peder H.|last2=Hertzel|first2=Anthony X.|date=2000|publisher=Minnesota Ornithologists' Union|page=1}}</ref> and a [[Mi'kmaq]] saga describing Kwee-moo, the loon who was a special messenger of [[Glooscap]] (Glu-skap), the tribal hero.<ref>{{Cite book|url=https://books.google.com/books?id=rCtL2WL0XCYC&pg=PT48|title=The Algonquin Legends Of New England|last=Leland|first=Charles Godfrey|date=2012|publisher=Jazzybee Verlag|isbn=978-3-8496-2265-7 |pages=48|edition=Annotated}}</ref> The tale of the loon's necklace was handed down in many versions among [[Pacific coast|Pacific Coast]] peoples.<ref>{{Cite book|title=Field Guide to Birds of the Northern California Coast | last1=Stallcup | first1=Rich | last2=Evens | first2=Jules | date=2014 | publisher=University of California Press | isbn=978-0-520-27616-1 | location=Berkeley, CA |page=60}}</ref> The [[Delaware Tribe of Indians|Delaware]] in the east of North America and the [[Buryats]] of Siberia also had creation stories involving the loon.<ref name="Cocker" />

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",<ref>{{Cite book|title=Fróðskaparrit 53|last=Bloch|first=Dorete|publisher=Faroe University Press|year=2006|isbn=978-99918-41-03-8|page =53}}</ref> and "ember-goose".<ref>{{Cite book|title=The Scientific Nomenclature of Birds in the Upper Midwest|last1=Sandrock|first1=James|last2=Prior|first2=Jean C.|date=2014|publisher=University of Iowa Press|isbn=978-1-60938-225-4|location=Iowa City, IA| page=63 }}</ref> An old colloquial name from [[New England]] was ''call-up-a-storm'', as its noisy cries supposedly foretold stormy weather.<ref>{{cite journal|last=McAtee|first=W.L|year=1951|title=Bird names connected with weather, seasons, and hours|journal=American Speech | volume=26 | issue=4 | pages=268–278 | doi=10.2307/453005 | jstor=453005 }}</ref> 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.{{sfn|Lockwood|1984|pp=24, 30, 39, 58}}

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]].<ref name= Cocker />

=== Popular culture ===
The 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 then current 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 collecting|egg collector]], at a time when the latter hobby was not widely considered to be harmful.<ref>{{cite web|last=McGinnis|first=Molly|date=February 2004|title=Totem Animals in Swallows & Amazons: Great Northern?|url=http://www.allthingsransome.org/literary/totemgreatnorthern.html|access-date=26 March 2010|work=[[All Things Ransome]]}}</ref><ref name="Hardyment">{{cite book|last=Hardyment|first=Christina|title=Arthur Ransome & Captain Flint's Trunk|publisher=Jonathan Cape|year=1984|isbn=978-0-224-02989-6|location=London|pages=201–204}}</ref>

[[Major League Soccer]] club [[Minnesota United FC]] uses the loon in its crest and nickname, as well as a mascot.<ref>{{cite news|last=La Vaque|first=David|date=27 October 2016|title=Minnesota United to donate portion of 2017 season ticket purchases to help loons|work=[[Star-Tribune]]|location=Minneapolis|url=http://www.startribune.com/minnesota-united-to-donate-portion-of-2017-season-ticket-purchases-to-help-loons/398911731/|access-date=8 September 2017}}</ref>

[[Minor League Baseball]] team [[Great Lakes Loons]], located in [[Midland, Michigan]] also uses the loon in its logo and name, as well as a mascot.<ref>{{cite web | url=https://www.milb.com/great-lakes | title=Great Lakes Loons }}</ref>

==== Films ====
The wailing call of the loon is widely used in film and television to evoke wilderness and suspense,<ref>{{Cite web|date=2002-06-14|title=The birds of Hollywood: An unnatural history|url=https://www.salon.com/2002/06/13/ornithology/|access-date=2021-10-13|website=Salon|language=en}}</ref> and is referenced in songs such as "[[Old Devil Moon]]" ("wanna laugh like a loon").<ref name="Cocker">{{cite book | last = Cocker | first = Mark |author2=Mabey, Richard |title = Birds Britannica | year=2005 |location=London | publisher=Chatto & Windus | isbn=978-0-7011-6907-7| pages=306–307}}</ref>

Loons are featured prominently in the 1981 film ''[[On Golden Pond (1981 film)|On Golden Pond]]''.<ref name="tex">{{cite journal|last=Wolcott|first=James|year=1982|title=Big frogs, small pond|journal=[[Texas Monthly]]|volume=10|issue=1|page=120}}</ref> Its distinctive sound also appeared in [[Conan the Barbarian (1982 film)|''Conan the Barbarian'']], [[Out of Africa (film)|''Out of Africa'']], [[Platoon (film)|''Platoon'']], [[Guinevere (1999 film)|''Guinevere'']], [[Harry Potter and the Prisoner of Azkaban (film)|''Harry Potter and the Prisoner of Azkaban'']], ''[[Rick and Morty]]'', [[Watchmen (2009 film)|''Watchmen'']], [[Godzilla (2014 film)|''Godzilla'']], ''[[Kubo and the Two Strings]]'', ''[[Avengers: Infinity War]]'', [[Pet Sematary (2019 film)|''Pet Sematary'']], [[1917 (2019 film)|''1917'']] and ''[[Avengers: Endgame]]'', among others.<ref>{{Cite web|last=Cascione|first=Marie|date=2021-10-13|title=Why Hollywood loves this creepy bird call|url=https://www.vox.com/videos/2021/10/13/22725104/hollywood-creepy-bird-call-common-loon|access-date=2021-10-13|website=Vox|language=en}}</ref><ref>{{Cite web|last=McCarter|first=Reid |title=A look at why the loon's call is used as TV and movies' go-to wilderness sound effect|url=https://www.avclub.com/a-look-at-why-the-loons-call-is-used-as-tv-and-movies-g-1847872228|access-date=2021-10-13|website=[[The A.V. Club]]}}</ref><ref>{{Cite web|last=Blaine|first=Valerie|date=2020-02-17|title=Why the loon's iconic call says so much|url=https://www.dailyherald.com/entlife/20200217/why-the-loons-iconic-call-says-so-much|access-date=2021-10-13|website=Daily Herald|language=en-US}}</ref><!-- https://birding-world.com/hollywood-goes-birds/
https://www.ledgertranscript.com/grBackyardNaturalist-ml-062921_-41154472
https://books.google.com/books?id=XyfVAwAAQBAJ
https://books.google.com/books?id=RPwyEAAAQBAJ -->

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.<ref>{{Cite news|url=https://www.nytimes.com/2016/06/17/movies/finding-dory-review-pixar.html|title=Review: In 'Finding Dory,' a Forgetful Fish and a Warm Celebration of Differences|last=Scott|first=A.O.|date=15 June 2016|work=The New York Times|access-date=14 August 2017|archive-url=https://web.archive.org/web/20170511020310/https://www.nytimes.com/2016/06/17/movies/finding-dory-review-pixar.html|archive-date=11 May 2017}}</ref>

==Notes==
{{notelist}}

== References ==
{{Reflist}}

==Sources==
{{refbegin}}
*{{ cite book | editor1-last=Cramp | editor1-first=Stanley | display-editors=etal | editor1-link=Stanley Cramp | year=1977 | chapter=''Gavia immer'' Great Northern Diver | title=Handbook of the Birds of Europe the Middle East and North Africa. The Birds of the Western Palearctic. Volume I: Ostrich to Ducks | place=Oxford | publisher=Oxford University Press | isbn=978-0-19-857358-6 | pages=56–61 }}
*{{cite book | last=Johnsgard | first=Paul A. |author-link=Paul Johnsgard | year=1987 | title=Diving Birds of North America | location=Lincoln, NE | publisher=University of Nebraska Press | isbn=978-0-8032-2566-4 | url=https://archive.org/details/divingbirdsofnor0000john }}
*{{cite book | last=Lockwood| first=W.B. | year=1984 | title=Oxford Book of British Bird Names | location=Oxford | publisher=Oxford University Press |isbn=978-0-19-214155-2 }}
{{refend}}

== External links ==
{{Commons category|Gavia immer|the common loon}}
{{Wikispecies|Gavia immer}}
* {{usurped|1=[https://web.archive.org/web/20001022011840/http://www.bird-stamps.org/cspecies/800400.htm Common Loon stamps]}} – bird-stamps.org
* [https://web.archive.org/web/20121008081332/http://www.arkive.org/common-loon/gavia-immer/video-00.html Common loon (''Gavia immer'')] – [[ARKive]]
* {{InternetBirdCollection|great-northern-diver-gavia-immer|Great Northern Diver (''Gavia immer'')}}
* [http://www.loon.org/ The Loon Preservation Committee]
* {{VIREO|Common+Loon|Common loon}}

{{Loons}}
{{portalbar|Birds|Animals|Biology}}

{{Taxonbar|from=Q190342}}
{{Authority control}}
{{Use dmy dates|date=March 2018}}

[[Category:Gaviiformes]]
[[Category:Native birds of Alaska]]
[[Category:Birds of Canada]]
[[Category:Birds of Greenland]]
[[Category:Birds of Iceland]]
[[Category:Native birds of the Northeastern United States]]
[[Category:Native birds of the Northwestern United States]]
[[Category:Birds described in 1764]]
[[Category:Taxa named by Morten Thrane Brünnich]]
[[Category:Articles containing video clips]]