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Black-throated loon
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===Breeding=== [[File:Black throated loon family feeding on Lake Sträken, Sweden.jpg|thumb|Black-throated loon family feeding on [[w:sv:Stråken (Mullsjö)|Lake Stråken]], Sweden]] This species usually nests on the ground<ref name="Petersen1979">{{cite journal|last=Petersen|first=Margaret R.|title=Nesting ecology of arctic loons|journal=The Wilson Bulletin|volume=91|issue=4|year=1979|pages=608–617}}</ref> within about {{convert|1|m|ft}} of the lake it breeds at.<ref name="Hakeetal.2005"/> This loon also sometimes nests on vegetation, like ''[[Arctophila fulva]]'', that has emerged from lakes. The nest site is often reused the next year.<ref name="BergmanDerksen1977"/> The nest itself is oval-shaped<ref name="Petersen1979"/> and built mostly by the female<ref name="Sjolander1978"/> out of heaped plant material like leaves and sticks.<ref name="Hauber2014">{{cite book|last=Hauber|first=Mark E.|title=The Book of Eggs: A Life-Size Guide to the Eggs of Six Hundred of the World's Bird Species|url=https://books.google.com/books?id=evQvBAAAQBAJ|date=1 August 2014|publisher=University of Chicago Press|location=Chicago|isbn=978-0-226-05781-1|page=53}}</ref> The nest is about {{convert|23|cm|in}} across. Families of black-throated loons often move their nest site from the original nest ponds they inhabited to wetlands nearby after the chicks reach two weeks of age. The journey is generally less than {{convert|150|m|ft}}.<ref name="BergmanDerksen1977"/> In the southern portion of its range, this loon starts to breed in April, whereas in the northern parts of its range, it waits until the spring thaw,<ref name="hbw"/> when there is adequate water for it to take off.<ref name="Petersen1979"/> It usually arrives before the lake thaws, in the latter case.<ref name="Sjolander1978">{{cite journal|last1=Sjolander|first1=Sverre|title=Reproductive behaviour of the black-throated diver ''Gavia arctica''|journal=Ornis Scandinavica|volume=9|issue=1|year=1978|pages=51–65|issn=0030-5693|doi=10.2307/3676139|jstor=3676139}}</ref> Before copulation, the female hunches its neck and swims close to the shore until it finds a suitable place and then lies down on the shore. The male sometimes adopts the same posture as the female. During this time, the only vocalization made is a one note "hum". During copulation, the male, coming ashore, mounts the female and occasionally flaps its wings loudly. After this, the male returns to the water and {{birdgloss|preens}} itself. The female stays ashore for a maximum of about 23 minutes and usually starts to build the nest.<ref name="Sjolander1978"/> [[File:Gavia arctica MWNH 1918.JPG|thumb|Eggs, Collection [[Museum Wiesbaden, Germany]]]] The black-throated loon lays a clutch of two, very rarely one or three,<ref name="hbw"/> {{convert|76|by|47|mm|in}} eggs that are brown-green with darker speckles. These eggs are incubated by both parents for a period of 27{{nbsp}}to 29{{nbsp}}days,<ref name="Hauber2014"/> with the female spending the most time incubating. During incubation, this bird turns its eggs. The interval between when they are turned is very irregular, ranging from one minute to about six hours.<ref name="Sjolander1978"/> After they hatch, the mobile young are fed by both parents for a period of weeks.<ref name="Hauber2014"/> The chicks fledge about 60{{nbsp}}to 65{{nbsp}}days after hatching, and achieve sexual maturity after two to three years.<ref name="hbw"/> Nesting success, whether or not at least one chick will hatch from any given nest, is variable year to year, ranging from under 30% to over 90%.<ref name="BergmanDerksen1977"/> For clutches of two eggs, the average nesting success is about 50%, whereas in clutches with only one egg, this rate is about 60%.<ref name="MudgeTalbot1992"/> The nesting success is influenced most by predation,<ref name="Petersen1979"/> and flooding.<ref name="MudgeTalbot1992">{{cite journal|last1=Mudge|first1=G. P.|last2=Talbot|first2=T. R.|title=The breeding biology and causes of nest failure of Scottish black-throated divers ''Gavia arctica''|journal=Ibis|volume=135|issue=2|year=1992|pages=113–120|issn=0019-1019|doi=10.1111/j.1474-919X.1993.tb02822.x}}</ref> Some of the adults that lose their clutch early in the incubation period renest. Most of the time, only one chick survives to fledge, the other dying within seven days of hatching.<ref name="BergmanDerksen1977">{{cite journal|last1=Bergman|first1=Robert D.|last2=Derksen|first2=Dirk V.|title=Observations on arctic and red-throated loons at Storkersen Point, Alaska|journal=[[Arctic (journal)|Arctic]]|year=1977|volume=30|issue=1|pages=41–51|doi=10.14430/arctic2682|url=https://arctic.journalhosting.ucalgary.ca/arctic/index.php/arctic/article/download/2682/2659|doi-access=free}}</ref> In Scotland, a study concluded that a single pair usually fledges a chick, on average, 25% of the time per year.<ref name="hbw"/> This can be increased by artificial means, such as constructing rafts for loons to nest on.<ref>{{cite journal |last=Hancock |first=Mark |year=2000 |title=Artificial floating islands for nesting Black-throated Divers ''Gavia arctica'' in Scotland: construction, use and effect on breeding success |journal=Bird Study |volume=47 |pages=165–175 |doi=10.1080/00063650009461172 |issue=2 |doi-access=free |bibcode=2000BirdS..47..165H }}</ref> Whether or not there is at least one chick fledged is influenced by the density of fish in the breeding lake; a lake with a higher density of fish usually reduces the chance that a pair will fledge a chick, even though this loon feeds mainly on fish. There are two factors that might contribute to this; the first being that aquatic insects, an alternative food source for chicks, are more dense when there are less fish, and the second being that a higher density of fish means more [[northern pike]], a predator of small chicks.<ref name="Eriksson1986">{{cite journal|last1=Eriksson|first1=Mats O. G.|title=Reproduction of black-throated diver ''Gavia arctica'' in relation to fish density in oligotrophic lakes in southwestern Sweden|journal=Ornis Scandinavica|volume=17|issue=3|year=1986|pages=245–248|issn=0030-5693|doi=10.2307/3676833|jstor=3676833}}</ref>
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