AGE – BEST CRITERIA:
1cy birds show moult contrasts in the wing. Typically, moult limits are found within the TT or between the TT and SS. Those with a more limited post-juv moult only replace the inner one-third GC but most moult all GC (the moult limit is then found between the outermost GC and PC). Often 1-3 AL are also included in the post-juv moult. 2cy+ birds show a uniform and fresh plumage with, on average, less orange/brown colouration, tending to be dominated by darker glossier brown and black tones.
Most ad birds are not possible to age further than 2cy+ due to the complete post-br moult. However, some ad arrest their moult before completion of SS and/or underwing GC. Hence, feathers retained in the post-br moult are still useful during autumn as they can usually be assigned to either juv or ad type, and thereby give the possibility to separate some 2cy and 3cy+ birds.
- Juv PP (especially outer PP) and SS are more worn, being of poorer quality compared to ad ones. The feathers are rather narrow with tapering and pointed tips (outer web tips of the SS and inner web tips of the inner PP are always noticeably convex). They show, on average, larger orange/brown wedges than ad resulting in a dominant rufous appearance.
- Juv PC have broad orange/brown tips similar in colour to the neighbouring orange/brown wedges. They are narrower than ad, taper slightly and have rounded tips with a bleached dark brown ground colour.
- Juv GC are rich orange/brown with less distinct and narrower black bars (often with limited or no grey centres) compared with ad. The feathers are approximately one-quarter shorter than subsequent generations.
- Underwing GC and underwing PC are oblong, narrow, and taper towards a rounded tip. The darker areas are cold brown.
- Juv TT are slightly or moderately worn with orange/brown bars contrasting with bleached dark brown bars containing grey centres. They are also less dense in structure than subsequent generations.
- Juv RR are rounder, more worn and have a browner ground colour to the upper-side of the grey tips compared with ad.
- Whole plumage fresh, dense and lacks moult contrasts.
- PP and SS broad and glossy with bulbous blunt tips, often a slight concave tip to the inner web of the inner PP and the outer web of SS. Ad show, on average, smaller orange/brown wedges than juv, giving a cold brown/black dominance to the flight feathers.
- PC with narrow beige or white tips, paler than the neighbouring orange/brown wedges. They are broad, blunt-tipped and have a glossy black ground colour.
- GC are less orange/brown than juv with thick, distinct black bars (often with obvious grey centres). All feathers are a similar length.
- Underwing GC and underwing PC are parallel sided, broad and have a blunt tip. The darker areas are glossy grey/black.
- TT fresh with orange/brown bars contrasting with glossy black bars containing mottled grey centres.
- RR all fresh with silver-grey upper-side tips.
- As 2cy+ but has at least one retained juv S and/or underwing GC.
- As 2cy+ but has at least one retained post-br S and/or underwing GC from the previous year’s SC moult.