The Siberian jay (Perisoreus infaustus) is a small jay with a widespread distribution within the coniferous forests in North Eurasia. The specific epithet ‘infaustus’ is Latin and means "unlucky" or "unfortunate" as Siberian jays were formerly considered a bad omen.
The adult plumage of Siberian jays is greyish brown, with a dark brown head, paler forehead, and buff breast. The rump is yellowish and the chin and throat are grey. There is also rufous streaking on the outer feathers, and the bill and legs are black. Their overall coloration is fairly inconspicuous to visually conceal them from predators within their forest habitat. The plumage is also very soft and downy for insulation against extreme cold in winter. Siberian jays molt once per year between mid-June and mid-September.
Siberian jays are found from Scandinavia to northern Russia and Siberia. They are native to Norway, Sweden, Finland, Russia, Mongolia, Kazakhstan and China. They are vagrants in Belarus, Estonia, Latvia, Poland, Slovakia and Ukraine. Siberian jays are largely sedentary, but populations in the east part of the range perform some southward movement in winter. These birds inhabit northern boreal spruce, pine, cedar, and larch forests. They prefer dense, mature forest habitats with closed canopies within lowlands and foothills. Spruce forest is the preferred foraging and nesting habitat because the denser foliage of spruce than other local conifers better conceals the bird from the watchful eyes of predators.
Siberian jays have a complex and unusual social structure. These birds live in small flocks of 2-7 individuals, with the dominant breeding pair at the center of the group; alongside retained multigenerational offspring and unrelated immigrants. Within a group, there is a dominance hierarchy; whereby males are dominant over females and breeders are dominant over non-breeders; with some male non-breeders being dominant over female breeders. Flock composition varies, with some comprising only family members, families associated with nonrelated immigrants, and others containing only nonrelated individuals. Siberian jays are aggressive to non-related intruders on their territory. They will either approach and force an intruder away or chase it in flight. When foraging, Siberian jays often stay within the closed-canopy forest to avoid detection by predators, although they may occasionally forage in open areas. They forage in flocks comprising 3-5 individuals within their large territory. Siberian jays are mostly silent but can utter a loud screech. The song, which is performed by both sexes, mainly during the breeding season and heard only from a short distance, comprises a wide repertoire of sounds. These range from sequences of separate soft and harsh notes to bouts of whistling, creaking, and trilling, sometimes incorporating mimicked song of other birds. Siberian jays also engage in nepotistic alarming calling, which may serve to warn conspecifics of an approaching predator.
Siberian jays are omnivorous and feed mainly on berries, seeds, insects, and spiders. They will also eat large carcasses killed by mammalian predators such as wolves and wolverines. Other occasional food items include eggs of small birds, tit nestlings, snails, slugs, small mammals, and lizards. In autumn and winter, berries (especially bilberries and cowberries) are typically collected and stored behind loose bark or in hanging beard lichen and between forked twigs.
Siberian jays are monogamous; they form pairs that stay together and hold the same territory for life. These birds locate their nests in a pine or spruce tree 4-6 m (13-20 ft) above ground within dense foliage hidden from nest predators. The nest is a loose cup of dry twigs broken off trees by the jays and is thickly lined with beard lichen moss, down feathers, cobwebs, reindeer fur, and wasp nest fragments; the lining serves as necessary insulation against the extreme winter cold. Both partners collect nest material, but only the female builds the nest. The female lays 1-5 eggs in March-April. The eggs are pale green, blue, or grey and spotted with grey and brown. The eggs are incubated for about 19 days entirely by the female, whilst the male provides all the food for the brooding female and the chicks. Newly hatched chicks are almost bare and are closely covered by the female. The young fledge in mid-May to early June and leave the nest around this time, 18-24 days after the first chick has hatched; although they usually hide within tree branches on the territory until they are able to properly fly. Parents continue to feed the young for about 3 weeks after fledging, with all of them remaining in a family group throughout summer, autumn, and winter. Most mature young disperse from the natal territory in their first summer 4-8 weeks after fledging to join new groups. If offspring have not yet dispersed by the time they are 8 weeks old, they usually remain in the natal territory at least through the first winter. The retained, socially dominant offspring remaining on the natal territory may wait for up to 5 years before dispersing, whenever a suitable breeding opportunity arises. Young birds may inherit the new territory to which they disperse and at which they breed. However, if there are no vacant territories to occupy, juveniles can join a different family group to gain feeding advantages and may even attempt to establish their own territory at the age of 2-3 years.
Siberian jays are threatened by habitat degradation through the encroachments of forestry, road building, settlements, and agriculture. Modern European forestry practices in particular may be lessening the quality of breeding habitats for Siberian jays by depriving the birds of sufficient foliage cover. This may occur through forest thinning, whereby lower-quality trees are regularly removed from forest stands. Another practice that may threaten Siberian jays has been the large-scale removal of stands of native spruce to be replaced with pine, potentially leading to the loss of sufficient visual cover of nesting activity from predators with the removal of spruce. In Finland, spruce has also been declining faster than other forest types, and loss and fragmentation of spruce forests through forestry have been linked with population declines here. Anthropogenic habitat loss may be interacting with natural threats from predators. Human activity may also favor nest predators such as Eurasian jays through supplemental feeding and refuse dumpling, thereby compounding the predation pressure on Siberian jays through visual exposure to predators. Finally, destruction by felling of winter food storage in trees near territories during winter may also destroy winter food caches.
According to the IUCN Red List, the total population size of the Siberian jay is 4,295,000-7,600,000 mature individuals. In Europe, the breeding population consists of 430,000-761,000 pairs, which equates to 859,000-1,520,000 mature individuals. Currently, this species is classified as Least Concern (LC) on the IUCN Red List but its numbers today are decreasing.
