The Pine siskin (Spinus pinus) is a North American bird in the finch family. It was formally described in 1810 by the American ornithologist Alexander Wilson under the binomial name Fringilla pinus. The specific epithet pinus is the Latin word for a "pine-tree".
Adults of this species are brown on the upperparts and pale on the underparts, with heavy streaking throughout. They have short forked tails. Their bills are conical like most finches but are more elongated and slender than those of other co-occurring finches. Variably, pine siskins have yellow patches on their wings and tails, which may also consist of white streaks on the wings. Although they can be confused with the more inexperienced for other finches or even American sparrows, Pine siskins are distinguished by their heavy streaking, relatively slender bills, notched tails, yellow or whitish patches on the wings, and smallish size.
The range of these birds spreads throughout almost all of Canada, Alaska, and the northern parts and western mountains of the United States. Pine siskins mostly breed in coniferous forests, though they can be found in the mixed forests of the Puget Trough. During the winter period and migration, they can be seen in many different semi-open areas, such as forest edges and fields of weeds.
Pine siskins are mainly active during the daytime, although some may seek food by moonlight when it is scarce. They form flocks at all times of the year, winter flocks being sometimes quite large. They are very common in urban areas at bird feeders. They are active foragers, climbing around nimbly amongst forest canopies and hedgerows, frequently hanging upside-down. They will occasionally look for food on larger branches, similar to a nuthatch. Like many other finches, their flight pattern is undulating and they often emit aerial contact calls. These birds are usually described as resident, but especially in winter, they can be nomadic and irruptive. Their movements follow the distribution and availability of seeds. When cone crops are small in the north, many pine siskins winter over in Washington on the western slope of the Cascades.
Pine siskins are herbivores (granivores) and carnivores (insectivores). In winter, they eat mostly small seeds, especially thistle, birch, red alder, and spruce. They also glean the seeds of grass, dandelions, chickweed, sunflowers, and ragweed. In summer they will eat many insects, especially aphids, feeding them to their chicks.
Pine siskins are monogamous, with pairs forming within winter flocks. They nest either in loose colonies or as separate pairs. Breeding starts in January and February. Their nests are hidden well, on a horizontal branch some distance from a conifer’s trunk. The female constructs a large, shallow cup-shaped nest of twigs, grass, rootlets, bark strips, leaves, and lichen, lining it with moss, plant down, feathers, and hair. The female lays 3 to 4 eggs and incubates them for about 13 days. Her mate brings her food during the incubation period and the first few days once the eggs hatch. Then both parents bring food. After 13 to 17 days the young birds leave the nest and their parents feed them for about another 3 weeks.
Domestic cats, red squirrels, jays, hawks and crows prey on the birds and their eggs. Loss of habitat due to forest-clearing may be mitigated by new coniferous forests planted commercially, and by the pine siskin’s adaptability at nesting in ornamental trees and shrubs.
According to the All About Birds resource, the total breeding population size of the Pine siskin is around 40 million individuals. Currently, this species is classified as Least Concern (LC) on the IUCN Red List, and its numbers today remain stable.
Pine siskins provide an important function by eating many species of destructive insect and weed pests.