Editing Common loon (section)

===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" />