The Eurasian Siskin: A Tiny Finch Full of Surprises

The siskin is a small finch with a short tail, measuring around 11–12.5 centimetres from bill to tail and having a wingspan of approximately 20–23 centimetres. Its body weight generally falls between 10 and 18 grams.

There is a clear difference in appearance between male and female siskins. Adult males have a grey-green back, a yellow rump, and a tail marked with yellow along the sides and black at the tip. Their wings are black and crossed by a conspicuous yellow stripe. The breast is yellowish higher up and gradually becomes paler and more heavily streaked toward the lower body. A black bib is present on the throat, while the head features yellow auricular areas and a black crown. The extent of black on the bib varies considerably among males, and larger bibs have been associated with higher social status within a flock.

Females are generally more olive-coloured than males. Their crown and auricular areas have a greenish tone, while the bib is white and the rump is a somewhat streaked pale yellow. Young birds resemble females, although their colours are duller and their overall plumage is less vivid.

The siskin's bill reflects its specialized feeding habits. It is relatively powerful but remains narrow enough to handle the small seeds that make up much of the bird's diet. Its legs and feet are dark brown, while the eyes are black.

Like many other finches, the siskin flies in a quick, bouncing manner, with a characteristic undulating flight.

Although the siskin is generally easy to identify, it can sometimes be mistaken for species such as the citril finch, greenfinch, European serin, or the closely related pine siskin. European siskins are often noticeably brighter than pine siskins. Adult males of the European species display vivid green and yellow plumage, a black cap, and an unstreaked throat and breast, features that are absent from the typical pine siskin. Adult female European siskins also commonly show green and yellow shades, including yellow on the supercilium and sides of the breast, green on the mantle, and yellow on the rump.

Typical adult pine siskins lack these strong green and yellow tones. Juveniles can briefly show a yellowish-buff wash on the underparts and buff-coloured wingbars before their autumn migration. The underside of a European siskin is generally clean white, whereas the pine siskin usually has a more soiled or subdued background colour. Female and juvenile European siskins often have an unstreaked central belly and lower breast, while the streaking of most pine siskins continues across nearly the entire underparts.

European siskins usually have broad yellow wingbars. Pine siskins generally have narrower, buff-white wingbars combined with a bright yellow flash near the bases of the primary feathers. Pine siskins also tend to possess a longer bill with a relatively straight culmen, compared with the shorter bill and curved culmen of the European siskin.

A green colour form of the pine siskin does occur, although it represents only about one percent of the population. These individuals more closely resemble female European siskins. They can be distinguished by a yellow wash on the undertail-coverts, the absence of yellow on the supercilium, less extensive streaking below, and a stronger yellow colour at the bases of the tail and flight feathers. The precise difference in yellow colouring on the underparts requires further research.

Naming

The bird is commonly known as the European siskin, common siskin, or simply siskin. Other historical or regional names include Black-headed Goldfinch, barley bird, and aberdevine.

Distribution

The siskin occurs across much of Eurasia as well as parts of northern Africa. Its breeding range is divided into two principal areas on opposite sides of the Palearctic region, extending through eastern Asia and central and northern Europe.

The species remains present throughout the year in much of Central Europe and in several mountain regions farther south. It also occurs across northern Scandinavia and Russia, while wintering populations can be found around the Mediterranean basin and the Black Sea region.

In China, breeding populations occur in the Khingan Mountains of Inner Mongolia and in Jiangsu province. During summer, birds can also be found in Tibet, Taiwan, the lower Yangtze River valleys, and along the southeastern coast.

The Eurasian siskin is an occasional visitor to North America. North America also has a closely related species known as the pine siskin, Spinus pinus.

The species has an unusual pattern of seasonal movement. Every few years, much larger numbers travel south, resulting in a significant increase in wintering birds on the Iberian Peninsula. Several explanations have been proposed for these irregular movements. One possibility is that unusually heavy crops of Norway spruce seeds in central and northern Europe increase the population and encourage greater dispersal. Another explanation is that increased migration occurs when the preferred seeds of alder or birch become scarce.

Outside the breeding season, siskins frequently gather into large flocks, sometimes associating with redpolls.

Status

The global siskin population is estimated to number between 20 and 36 million individuals. The European population is thought to consist of approximately 2.7 to 15 million breeding pairs.

There is currently no indication of a significant worldwide population decline. As a result, the IUCN classifies the species as Least Concern. The siskin is also included in Annex II of the Berne Convention as a protected bird species.

Behavior

Siskins are energetic and constantly active birds. They are highly sociable and often form compact groups, particularly throughout autumn and winter. They are relatively tolerant of people and can sometimes be watched from quite close range.

Their behavior changes during the breeding season. At that time they become more cautious, solitary, and difficult to locate. This secretive nature contributed to a German legend claiming that siskins protect a magical stone inside their nests that gives them the power to become invisible.

The species is also among the relatively few birds reported to display allofeeding. In this behavior, lower-ranking birds regurgitate food for dominant members of the group. Such interactions help strengthen relationships within the flock and indicate the presence of a social hierarchy.

Habitat

Siskins are not birds that necessarily remain in the same location throughout the year. Their breeding, feeding, and wintering areas can change considerably from one year to another.

They generally inhabit wooded landscapes at particular elevations on mountain slopes and show a preference for damp environments. Coniferous forests, especially spruce woodland, are particularly important during the breeding period.

The nest is constructed in a tree, where the female normally lays between two and six eggs. In Britain, the species was once a localized breeder, but its distribution expanded substantially following the increase in commercial conifer plantations.

Siskins also make use of mixed forests. During winter, they tend to move toward stubble fields, agricultural areas, and places containing seed-producing trees.

Reproduction

Pairs are commonly established during winter before the birds begin their migration. Males compete strongly with one another for access to females.

During courtship, a male may puff out the feathers on its crown and rump to make itself appear larger. It also spreads its tail and repeatedly sings to attract a mate. Courtship flights between trees occur as well, although they are generally less dramatic than those performed by some other finch species.

The nest is usually positioned toward the end of a fairly high conifer branch, where it remains concealed and difficult to detect. On the Iberian Peninsula, siskins have been recorded nesting in firs, Scots pine, and Corsican pine.

Small breeding colonies may consist of as many as six pairs, with neighboring nests positioned relatively close together. The nest itself is a small cup constructed from twigs, dried grass, moss, and lichen, with the interior lined with soft down.

The first young normally appear around the middle of April. The female lays between two and six eggs. These eggs can be white, pale grey, or light blue and are marked with small brown spots. They measure roughly 16.5 by 12 millimetres.

Incubation lasts approximately 10–14 days and is performed entirely by the female. The chicks hatch in an undeveloped state and remain dependent on the nest. They leave after about 15 days, while still only partly feathered.

After leaving the nest, the young remain in the surrounding area for as long as a month. Once their adult-like plumage has developed, they disperse. Siskins commonly produce a second brood, with breeding taking place from approximately the middle of June through the middle of July.

Food

The siskin is primarily a seed-eating bird, although the exact composition of its diet changes according to the season. It usually feeds among trees rather than searching for food on the ground.

During autumn and winter, seeds from deciduous trees form the main part of the diet, especially seeds from birch and, most importantly, alder. Siskins may also visit farmland and pasture, where they join other finches in feeding on the seeds of plants such as thistles, dandelions, Artemisia, knapweeds, and other flowering or herbaceous species including St. John's wort, meadowsweet, and sorrel.

During spring, when breeding takes place, siskins are commonly associated with coniferous woodland. At this time they feed heavily on conifer seeds, particularly those produced by trees belonging to the genera Abies, Picea, and Larix. They also consume seeds from elm and poplar trees.

When feeding their chicks, adults increase the amount of animal food they provide. Insects, especially beetles, become more important because their high protein content supports the rapid growth and development of the young.

During summer, the diet becomes more varied again. In addition to conifer seeds, siskins consume the seeds and other parts of herbaceous plants, including goosefoots and various members of the daisy family.