AGE – BEST CRITERIA:

• Juvenile GC are generally slightly narrower, less dense and more contrastingly patterned than adult. The pale spots in the tip of the outer vane are often rather large, quite distinct, oval-shaped and yellowish-tinged (more whitish when worn). The edge of the outer vane is warm brown, distinctly set-off against the black centre. As pointed out by Menzie & Malmhagen (2013), the black centre often shows a curved ’hook’ as it bends around the lower inner part if the pale spot. The black on the outer vane generally reaches the feather tip through a distinct and rather wide ’channel’ between the shaft and the pale spot.
• A moult contrast may be present in the GC (usually in the inner part of the arm) where the juvenile outer GC shows a weak contrast to the inner ones of adult type (see description below).
• Juvenile RR are generally slightly more worn, narrow and more pointed, but difficult birds are sometimes seen. The structure is often helpful, with the juvenile feathers being slightly less dense, less glossy and somewhat paler brownish.
• Juvenile PC are often slightly less dense and more loose/frayed than in adult, but difference is not always obvious. The brownish outer edge is usually rather narrow, but quite distinct, and does not reach the tip. This results, as noted by Menzie & Malmhagen (2013), in a broad dark feather centre that run with equal width, between the shaft and the brownish outer edge, all the way to the tip. Further, in a few birds, the juvenile PC show a diffuse blackish bar close to the tip, perhaps never seen in adult. 
• The colour of the iris in young 1cy is rather cold brownish-olive. However, the colour developes rather quickly, and some 1cy show a warm brown iris that is difficult to separate from 2cy+ already by early autumn.

• Whole plumage fresh, dense and lacks moult contrasts.
• Adult post-breeding GC are generally slightly broader and often a bit square-shaped at the tip, and the over all pattern is less contrasting. The pale spots in the tip of the outer vanes are often smaller (sometimes even absent), more diffuse, whitish and often quite square-shaped with clear ’corners’. The edge of the outer vane is often less warm brown (more olive-brown), and less distinctly set-off against the dark centre. The brown edge is often slightly broader than in juveniles (as broad as the pale spot) which means there is no, or less pronounced, ’hook’ in the dark centre, shown by many juveniles. The dark centre is usually somewhat paler (dark grey). If the dark centre reaches the tip (when fresh, the tip often shows a narrow brownish edge, preventing the dark centre from reaching the tip) it is usually through a slightly diffuse and narrow ’channel’ between the shaft and the pale spot.
• RR are generally slightly broader, more blunt tipped and often in better condition.
• PC are slightly more dense and crisp fresh, sometimes showing broader and more square-shaped tips. The outer edge is often slightly colder greyish-brown, a bit broader and more diffusely set-off towards the dark centre than in juveniles. Further, the greyish-brown outer edge often reaches further out on the feather, closer to the tip, sometimes even narrowly rounding the tip. This pattern gives a dark centre (between the shaft and outer edge) that narrows in width towards the tip.
• Colour of iris warm brown (sometimes reddish-brown).