The pine siskin is brown on its upperparts and pale on its underparts, with heavy streaks over its body. Their tails are short and forked. Like most finches, their beaks are conical but are longer and more slender. Pine siskins have patches of yellow on their tails and wings, and sometimes white streaks on their wings as well. They are distinguished from other birds by their smaller size, the streaking marks and whitish or yellow patches on their wings, their notched tail and relatively slender bills.
Their range 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.
The pine siskin eats mostly small seeds, especially thistle, birch, red alder and spruce. In summer they will also eat 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 three 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 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.