Editing Common tern (section)

===Moult===
[[File:Commonternprimary.jpg|thumb|Detail of primary feather|300px]]

Juveniles moult into adult plumage in its first October; first the head, tail, and body plumage is replaced, mostly by February, then the wing feathers. The [[Flight feather#Primaries|primaries]] are replaced in stages; the innermost feathers moult first, then replacement is suspended during the southern winter (birds of this age staying in their wintering areas) and recommences in the autumn. In May to June of the second year, a similar moult sequence starts, with a pause during primary moult for birds that return north, but not for those that stay in the winter quarters. A major moult to adult breeding plumage occurs in the next February to June, between forty and ninety per cent of feathers being replaced.<ref name=olsen/> Old primary feathers wear away to reveal the blackish barbs beneath. The moult pattern means that the oldest feathers are those nearest the middle of the wing, so as the northern summer progresses, a dark wedge appears on the wing because of this feather ageing process.<ref name=hume21/>

Terns are unusual in the frequency in which they moult their primaries, which are replaced at least twice, occasionally three times in a year. The visible difference in feather age is accentuated in the greater [[ultraviolet]] reflectance of new primaries, and the freshness of the wing feathers is used by females in mate selection.<ref name= bridgeeaton>{{cite journal |last=Bridge |first=Eli S |author2=Eaton, Muir D |year=2005 |title=Does ultraviolet reflectance accentuate a sexually selected signal in terns? |journal=Journal of Avian Biology |volume=36 |issue=1 |pages=18–21 |doi=10.1111/j.0908-8857.2005.03470.x}}</ref> Experienced females favour mates which best show their [[Fitness (biology)|fitness]] through the quality of their wing feathers.<ref name=bridge2004>{{cite journal |last=Bridge |first=Eli S |author2=Nisbet, Ian C T |year=2004 |title=Wing molt and assortative mating in Common Terns: a test of the molt-signaling hypothesis |journal=Condor |volume=106 |issue=2 |pages=336–343 |doi=10.1650/7381|s2cid=84393348 |doi-access=free }}</ref> Rarely, a very early moult at the nesting colony is linked to breeding failure, both the onset of moult and reproductive behaviour being linked to falling levels of the [[hormone]] [[prolactin]].<ref name=BB105>{{cite journal |last=Braasch |first=Alexander |author2=Garciá, Germán O |year=2012 |title=A case of aberrant post-breeding moult coinciding with nest desertion in a female Common Tern |journal=British Birds |volume=105 |pages=154–159}}</ref>