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.

[4][5] The specific epithet infaustus is Latin meaning "unlucky" or "unfortunate" as Siberian jays were formerly considered a bad omen.

[10] The lack of extra-parental care within the groups may be due to historic selection against cooperative breeding in the Siberian jay;[11] probably as an anti-predator strategy to avoid predator attention.

[9] With the colonisation of coniferous forests in Scandinavia just after the last ice age, the Siberian jay probably expanded its range from east to west in response to the newly formed suitable habitat resulting from climatic warming.

[12] The Siberian jay is the smallest of the western Palearctic corvids, weighing 75 to 90 g (2.6 to 3.2 oz)[13] and measuring about 30 centimetres (12 inches) in length.

[1] Siberian jays appear to be specially adapted to navigate in flight through dense forest despite being rather cumbersome flyers across open terrain.

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.

[19] Warning calls have been shown experimentally to decrease reaction time in response in an approaching predator and improve survival within non-breeding individuals.

[20] Alongside direct warning to family group members, nepotistic alarm calling by a breeding female may also function to divert predator attention away from her offspring.

[10] Siberian jays live in small flocks of 2–7 individuals, with the dominant breeding pair at the centre of the group;[24][25] alongside retained multigenerational offspring and unrelated immigrants.

Two different aggressive responses from territory holders within feeding grounds have been observed: (1) the intruder is approached and forced away, (2) or is chased in flight; although the latter behaviour is more costly to the aggressor.

[16][27] 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.

[31] The Siberian jay is single brooded and does not relay in a breeding season even after nest failure, but will wait until next year.

[16] 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;[15][27][31] although they usually hide within tree branches on the territory until they are able to properly fly.

[13] The retained, socially dominant offspring remaining on the natal territory may wait for up to five years before dispersing, whenever a suitable breeding opportunity arises.

[16][18] 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.

[35] 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.

[35] Especially in winter, Siberian jays will also venture into increasingly open areas to take and store small rodents for food when the latter are abundant.

[38] Predators of this species' eggs and young include squirrels, ravens, hooded crows, magpies and Eurasian jays.

[39] 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.

Excessive clearcutting has been linked with increased territory abandonment by Siberian jays, leading to strong decreases in the species' breeding success in affected areas.

The Siberian jay population has declined more than can be explained by anthropogenic forest clearance alone,[42] which may be attributable to increased nest exposure to avian predators and other human activities favouring these predatory species.

[12] Given this jay's high site fidelity, gene flow between subpopulations may have been low even before onset of modern forestry practices which have created the strong dispersal barriers.

[16] This was especially the case when forestry workers used to regularly leave patches of food scraps in the forest or around campfires for the jays to take.

[16] The Siberian jay has now gained flagship status as a conservation concern both because of threats from modern forestry and because active territories are considered a sign of high-quality biodiverse forest.