The Siberian jay (Perisoreus infaustus) is a small jay with a widespread distribution within the coniferous forests in North Eurasia. It has grey-brown plumage with a darker brown crown and a paler throat. It is rusty-red in a panel near the wing-bend, on the undertail coverts and on the sides of the tail. The sexes are similar. Although its habitat is being fragmented, it is a common bird with a very wide range so the International Union for Conservation of Nature has assessed its conservation status as being of "least concern".
Taxonomy and systematics
The Siberian jay was formally described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under the binomial name Corvus infaustus. Linnaeus specified the location as "Europae alpinis sylvis" but the type location was restricted to Sweden by Ernst Hartert in 1903. The specific epithet infaustus is Latin meaning "unlucky" or "unfortunate" as Siberian jays were formerly considered a bad omen. The Siberian jay is now placed together with the Canada jay and the Sichuan jay in the genus Perisoreus that was introduced in 1831 by Charles Lucien Bonaparte.
Five subspecies are recognised: the group individuals accompanying a breeding pair of Siberian jays do not help raise the offspring. The lack of extra-parental care within the groups may be due to historic selection against cooperative breeding in the Siberian jay; probably as an anti-predator strategy to avoid predator attention.
Description
thumb|In a spruce forest near [[Evenstad, Norway]]
The Siberian jay is the smallest of the western Palearctic corvids, weighing The adult plumage 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 colouration 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. although the average lifespan has been reported as 7.1 years.
Voice
The Siberian jay is mostly silent, but it can emit a loud screech similar to that of a buzzard (Buteo spp.). Both sexes perform the song, which is mainly heard during the breeding season from a short distance away, and it comprises a wide repertoire of sounds. These range from sequences of separate soft and harsh notes to bouts of whistling, creaking and trilling.. Siberian jays also engage in nepotistic alarming calls, which may serve to warn conspecifics of an approaching predator. Experimental studies have shown that warning calls decrease the reaction time of non-breeding individuals in response to an approaching predator and improve their survival rate. Alongside directly warning to family group members, a breeding female's nepotistic alarm calls may also divert a predator's attention away from her offspring.
This species prefers dense, mature forest habitat with a closed canopy in lowland and foothill areas. High breeding success has been linked to high foliage density, as this provides better hiding places for eggs and nestlings, making them less likely to attract predators. Additionally, the benefit of increased predator evasion through more hiding space would probably outweigh the cost of making predators more difficult to see by the jays within the dense foliage. The Siberian jay is notably selective in its choice of territory, with a typical territory comprising old dense spruce swamp with ample vegetation cover. alongside retained multigenerational offspring and unrelated immigrants. This may prevent extra-pair mating opportunities for the partner and thereby preserve inclusive fitness for both pair members. Although territories are firmly established, the jays can move to a neighbouring site if this is a better quality habitat where breeding success will be higher. The nest comprises a loose cup of dry twigs broken off trees by the jays They are laid 31 March – 22 April, with a variable clutch size of 1–5 and an incubation period of about 19 days. The Siberian jay is single brooded and does not relay in a breeding season even after nest failure, but will wait until next year. These early dispersers are generally subordinates which have been out-competed and displaced by one or a few socially dominant offspring that are retained. Parents provide retained offspring with reliable access to resources and antipredator protection,
At least one offspring usually remains with the parents after successful reproduction and regularly accompanies the pair for at least a year before dispersing; and tend to disperse much further than their dominant siblings, which more often move straight into a breeding position in a new territory. Flocks will also feed on large carcasses killed by mammalian predators such as wolves and wolverines. However, unlike in other corvids, this hidden food stash is not purposefully shared with siblings to increase inclusive fitness but is consumed by the hoarder or a pilferer for selfish use. Predators of this species' eggs and young include squirrels, ravens, hooded crows, magpies and Eurasian jays. The nest is constructed within the dense foliage to avoid attracting the attention of predators. Females also appear to lay smaller clutches under higher predation pressure, which may help to avoid attracting predator attention to the nest since fewer visits to the nest by the parent are necessary. Modern European forestry practices in particular may be lessening the quality of breeding habitats for the Siberian jay by depriving the birds of sufficient foliage cover. Another practice which may threaten the Siberian jay has been the large-scale removal of stands of native spruce to be replaced with pine, potentially leading to loss of sufficient visual cover of nesting activity from predators with removal of spruce. Anthropogenic habitat loss may be interacting with natural threats from predators. The Siberian jay population has declined more than can be explained by anthropogenic forest clearance alone, which may be attributable to increased nest exposure to avian predators and other human activities favouring these predatory species.