It is not possible to confuse the Purple Swamphen with any other species in the Iberian Peninsula. Its size and blue-colored plumage make it unmistakable.
The plumage is very similar in both sexes, so it is not a variable to consider in this process.
It is possible to recognize 3 different ages:
Juvenile specimen: they have a dark grey back and the rest of the upper parts (nape) and wing coverts are a faded blue-violet color. The chin is a dirty white color, the sides (flanks) are gray. The beak has a faded red color in the early stages, gradually turning into a bright red with a dark area on the sides. The legs are a faded red-ochre color.
1st/2nd-year specimen: these individuals have a plumage quite close to that of adults. It is possible to differentiate them by the head and upper parts, which are dyed a slightly faded blue-violet color. The chest and lower parts mix gray with white. The primary and secondaries are from the previous generation (retained), so they will be more worn than in adults. The 1st/2nd-year specimens have white undertail coverts, like adults, but in this case, the tips are stained with some strands of dark brown color.
Adult specimen: in this case, the back is already completely blue-violet. The rest of the upper parts, such as the nape, and wing coverts are pure blue-violet. The chin is cobalt blue. The beak and legs are a bright red color.
Purple Swamphen perform a complete post-nuptial molt, which usually ends in September. The post-juvenile molt, on the other hand, is partial and ends between the end of September and the beginning of October. In this process, body feathers are changed. Both age types perform a pre-nuptial molt in which only body feathers are changed.
Primaries: 10 per wing.
Secundaries: 13 per wing.