We have chosen to use the following terms and definitions which we believe are easy to understand for new ringers and (with some simplifications) are rather practical to apply to passerines of northern Europe:
Any of the above mentioned moults can be either complete or partial:
In a few species (or in single individuals), the complete moult may be interrupted due to e.g. periods of migration. Such pattern is described according to the following:
Any moult that is not complete results in a moult contrast which is a rather central term for a bird ringer, meaning a contrast between different generations of feathers. Careful study of the plumage, combined with knowledge of the species’ moult pattern, is the base for ageing birds. This is the reason why each species-chapter in this guide starts with a short, but important, presentation of the moult pattern – both as a moult-key, and in more detailed (but still easy to understand) text. In the moult-key we use single letter abbreviations for summer (S or s), winter (W or w), complete (C) and partial (p). The codes ‘sp’ and ‘WC’ should thus be read as ‘summer partial moult’ and ‘winter complete moult’ respectively.
The colour of the birds’ irises undergo a general development during the first years of living. The general rule (with exceptions of course) is that young birds show a dull and rather cold greyish iris that turns warmer brownish during the first year. During autumn, the difference is often readily apprehended through an eyepiece in good light conditions, but already during their first spring most species have developed a colour that is more difficult to tell from adults (3cy+). Thorough and long term studies of birds of known ages (i.e. recaptures) may give experience enough to, for some species, separate three age categories (which is only exceptionally done on passerines when ageing is based on plumage), but our advice is to be cautious in this respect. We suggest that logged ages should primarily be based on the assessment of the plumage and that the colour of the iris (or any other soft part) is treated as a supplementary character to add to the general impression. In this guide we have included photographs of irises rather irregularly, and this is mainly because of the difficulties to depict the character under studio conditions.
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