AGE – BEST CRITERIA:

Often difficult to age, and great care is required in the examination of the wing and tail. All birds, regardless of age, may show contrasts between two different generations of ad-type LC, MC and GC, which are of no use for ageing.

2cy show juv PP, PC and SS (but may have moulted innermost S6 during winter). Juv feathers may also still be present among RR, AL, CC and (rarely) TT. By now, these juv feathers are slightly bleached and rather worn and show a higher degree of contrast to the remaining post-juv/pre-br parts of the plumage than 3cy+ does. In difficult birds, make sure to check both wings since the moult may be slightly assymetrical and thereby offer better clues in one or the other.

Young birds could in theory be distinguished until the last juv feathers are shed during the post-br moult. However, with the progression of bleach and wear the two age groups may become inseparable. Due to individual variation we recommend that only typical spring/summer birds, showing a combination of characters, are aged.

2cy:

• Most birds show retained juv SS while all TT are of ad-type. A slight variation (plus/minus one feather) is seen with some birds showing moulted ad-type S6 while others (rarely) may retain juv longest T3.
• Regardless of the exact position, the above contrast (between ad-type TT and juv SS) is rather apparent because of slightly bleached juv SS.
• AL and CC may also still contain juv feathers, relatively worn and bleached. 
• Tips of PP often (but not always) showing more wear and bleach than in ad.
• Juv PC usually less dense and more worn than in ad, but differences are not always obvious.
• Tail variable and RR may consist of 1) two ad-type generations, 2) mix of ad-types and juv generation or 3) a uniformly juv generation.

3cy+:

• SS sometimes uniform pre-br, but often show contrast with 1-3 outer (and occasionally 1-2 innermost) SS retained post-br. These contrasts may sometimes be difficult to see but may, according to Jenni & Winkler (2020), be detected through a length difference in the feathers.
• No contrast visible between TT and pre-br SS.
• No juv feathers present in AL or CC. 
• Tips of PP often (but not always) in better condition, showing less wear and bleach than in 2y.
• Ad PC usually denser and in better condition than in 2y, but differences are not always obvious.
• Tail may consist of one or two ad-type generations.