"Age determination is quite tricky sometimes, because individual variation is wide. As WtEs mainly moult (change the feathers) every year from spring up to autumn - it is better to determine in our case the age in winters (not in years). They do not change all the feathers once, also not every feather every year, but main moulting time is during the warm season.
The eagles born in May 2010 are not one year old during their first winter, yet. And, for example, eagles born in 2007 are not four years old, yet - but their age we write 1w (first winter bird) or 4w (fourth winter bird), respectively.
Also ageing in calendar years is not good, because we need then to add one year at 1st of January, though no remarkable changes in feathering... Calendar years are good to use in summer for example."
Text by Urmas Sellis, Eagle Club
Picture upload by Looduskalender forum member Mutikluti
Additional information: How old is the Golden Eagle. Text and photos by Bird Club Leksand
http://www.leksandsfagelklubb.se/projek ... aging.html
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