AGE – BEST CRITERIA:
1cy show moult contrast in the wing, often (c. 35% of the birds) between post-juvenile MC and juvenile GC, but many birds (c. 56%) included 1-2 innermost GC. Very rarely, TT may also be included. Adults show a uniform and fresh wing. Shape and pattern of RR are useful as well as pattern and shape of PC.
A general difference in coloration and pattern of feathers is evident between 1cy and adult birds with 1cy birds most often having more extensive black areas on PC, RR, PP and SS. However, to determine the age based solely upon the amount of black in the feathers is not recommended since the variation is pronounced.
- Always show a moult contrast in the wing, often situated between MC and GC or with a few (1-4) inner GC being moulted. Rarely, one or more TT may have been included in the moult. The centra of post-juvenile coverts are, in the cases of inner GC, MC and LC in males and all coverts in females, black to dark ashy grey compared to the more faded grey or greyish-brown of the juvenile coverts (middle and outer GC in males are hard to asses since they often are dominantly white). Post-juvenile GC show deeper rusty brown tips than unmoulted juvenile, with the tips being less abraded, at least until late autumn-early winter.
- Juvenile RR generally show abraded and more pointed tips, and the blackish centra of R1 is more pointed than in adults. The margin between blackish centra and lighter edges of R1 is thinner and diffuse. R4 most often show extensive black markings.
- Juvenile PC show more extensive black areas as well as being (on average) slightly more pointed and abraded than in adult birds (however, there is a clear variation between individuals and between sexes).
- Uniform plumage lacking any moult contrast (though rare occasions of retained/forgotten feathers are known to occur).
- Whole wing and tail in better condition with broader and denser feathers, and (esp. in males) blackish and black parts being more intensely jet black and with better gloss. Wear might become harder to asses in late winter.
- Tips of RR generally blunter and broader with sharper contrast between black centra and broader light edges of R1. R4 in males show limited and well-defined black markings.
- Generally show less extensive black tips of PC and SS and sharper contrast between dark and light parts of the feathers, although variation (esp. in females) can be great.