Editing Common loon (section)

==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>