The siskin was first described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae as Fringilla spinus, in the 10th edition of Systema Naturae. In 1760, Brisson described the genus Carduelis, where this species was then placed. Recent taxonomic studies suggest placing it in the genus Spinus.
The scientific name Spinus is from the Ancient Greek spinos, a name for a now-unidentifiable bird. The English name is from German dialect sisschen or zeischen,
Despite being found across a wide area it is a monotypic species, that is, there are no distinct subspecies. This could be explained by a number of factors, such as spatial variability of individuals in breeding areas between years, the large overwintering area which supports a constant genetic interchange, and females having a number of clutches of eggs in one breeding season, each in a different place.
This bird may have reached America either from Asia or from Europe (Greenland/Iceland). It is the extant parental species of one of the Spinus/Carduelis three evolutive North American radiations of atriceps, pinus and dominicensis finches. It has been recorded both in the Aleutian Islands and the east: the Labrador Peninsula and St. Lawrence River mouth (Canada). This raises the possibility that this bird entered (or may still try to enter) America through Greenland/Iceland from Western Europe.
It has a rapid and bounding flight pattern that is similar to other finches.
The bird's appearance shows sexual dimorphism. The male has a greyish green back; yellow rump; the sides of the tail are yellow and the end is black; the wings are black with a distinctive yellow wing stripe; its breast is yellowish becoming whiter and striped towards the cloaca; it has a black bib (or chin patch) and on its head it has two yellow auriculas and a black cap. The amount of black on the bib is very variable between males and the size of the bib has been related to dominance within a flock. The plumage of the female is more olive-coloured than the male. The cap and the auriculas are greenish with a white bib and a rump that is a slightly striped whitish yellow. The young have a similar colouration to the females, with drab colours and a more subdued plumage.
The shape of the siskin's beak is determined by its feeding habits. It is strong although it is also slender in order to pick up the seeds on which they feed. The legs and feet are dark brown and the eyes are black.
