Order: Passeriformes.
Family: Fringillidae.
It is possible to confuse the Eurasian Siskin with other passerine or finch birds with similar tones and colors such as the European Greenfinch or the European Serin. The European Greenfinch also has yellow rectrices, but it is much larger in size. The R6 of the Eurasian Siskin (adult male) has black coloring on more than half of its outer vane, unlike the Greenfinch which only has the feather crest at the tip of the feather. On the other hand, the European Serin and the Citril Finch lack yellow in their rectrices.
The adult male has a black-colored crown and throat, although in the autumn months, these may be speckled with gray. The uppertail coverts are intense yellow. In the case of the adult female, the crown is tinged with greenish tones, with dark stripes and lacks the black spot on the throat. The nape has more yellow-green tones, more muted and striped with brown.
It is possible to recognize 2 different ages:
1st year / 2st year specimen: males often show a noticeable contrast between the greater coverts (changed in the post-juvenile molt) and the retained outer greater coverts, which in this case are shorter, less contrasted in black, and have a striking broken white edge. If all the greater coverts have molted, there is usually a boundary between the tertials (juvenile with a whitish edge, post-juvenile with a green-yellow edge) or between tertials and secondaries. Another case would be if the specimen has changed all the primary and tertiary coverts, so the contrast can be given in the alula and between primary and changed and retained secondaries. If the greater coverts have not molted, then the boundary is present between the lesser and median coverts. The rectrices (R6-R4) tend to be pointed due to wear.
Adult specimen: they usually show all the same-generation wing feathers, although it is possible to find an individual with interrupted molt. In the latter case, the retained feathers will have a great deal of wear. The rectrices have lost their pointed shape so they have a rounded tip and without contrast between the inner and outer ones.
The Eurasian Siskin undergoes a complete postnuptial molt, although, as we have previously discussed, it is possible to find some specimens with molt stopped in certain flight and alula feathers. This molt process usually ends between the months of September and October. The post-juvenile molt is, as a rule, partial, including the body feathers, lesser and median coverts, and occasionally some tertials. The post-juvenile molt usually ends between the months of September and November.
Primaries: 10 per wing.
Secundaries: 9 per wing.
Rectrices: 12.
