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: P. i. infaustus (Linnaeus, 1758) – Scandinavia to west Siberia (includes ruthenus) P. i. rogosowi Sushkin & Stegmann, 1929 – northeast European Russia to northcentral Siberia (includes ostjakorum) P. i. opicus Bangs, 1913 – east Kazakhstan, northwest China and south central Siberia P. i. sibericus (Boddaert, 1783) – central Siberia and north Mongolia (includes yakutensis and tkachenkoi) P. i. maritimus Buturlin, 1915 – southeast Siberia and northeast China
The Siberian jay differs from the other two species in its group-living behaviours. Unlike the other two species, where group individuals unrelated to breeding parents may help provision the young, 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.
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.
Description
The Siberian jay is the smallest of the western Palearctic corvids, weighing and measuring about in length. 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. There is one moult per year, which lasts from mid-June to mid-September. The longest recorded lifetime is 13 years 4 months for a bird ringed in Finland, although the average lifespan has been reported as 7.1 years.
Siberian jays appear to be specially adapted to navigate in flight through dense forest despite being rather cumbersome flyers across open terrain. This may explain their vulnerability to predation by raptors outside forests.Fabritius H. 2010. Effective population size and the viability of the Siberian jay population of Suupohja, Finland. Master's thesis, University of Helsinki.
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. They are also adept vocal mimics, and have been recorded mimicking the vocalizations of 20 bird species as well as Eurasian red squirrels. 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. However, females seem more able than males to differentiate between kin and non-kin. 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.
Distribution and habitat The Siberian jay is resident in the northern boreal spruce, pine, cedar and larch forests stretching from Scandinavia to northern Russia and Siberia. The species has an extensive range, estimated at and is native to Norway, Sweden, Finland, Russia, Mongolia, Kazakhstan and China. It is vagrant in Belarus, Estonia, Latvia, Poland, Slovakia and Ukraine. Despite being largely sedentary, some southward movement may occur in winter among individuals in the eastern part of the range.Madge S. 2009. Siberian Jay (Perisoreus infaustus). In: del Hoyo J, Elliot A, Sargatal J. Christie DA, de Jauna E.(eds). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona.
This species prefers dense, mature forest habitat with a closed canopy in lowland and foothill areas. Spruce forests are preferred for foraging and nesting habitat because spruce's denser foliage provides better concealment from predators than that of other local conifers. 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. Territories also tend to be structurally diverse, comprising scrub of various ages, groves and flood meadows. Therefore, active territories can be considered an indicator of a forest's high ecological diversity.
Behaviour and ecology The species has a complex and unusual social structure. Siberian jays live in small flocks of 2–7 individuals, with the dominant breeding pair at the centre 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. The composition of the flocks varies. Some comprise only family members and families associated with non-related immigrants. Others contain only nonrelated individuals. Immigrants that are unrelated to the existing population can be tolerated within the territory outside nesting areas.
Siberian jays are aggressive towards unrelated intruders on their territory. Two different aggressive responses have been observed in territory holders within feeding grounds: (1) the intruder is approached and forced away; or (2) the intruder is chased while in flight. However, the latter behaviour is more costly to the aggressor. Although breeders are considerably more aggressive toward immigrants than retained offspring, aggressive responses appear to be modified by social dominance within groups. For example, females have been found to receive significantly more aggression than males because males show more resistance on account of their higher social ranking, therefore resulting in a higher energy cost on the part of the aggressor. Siberian jays also appear to recognise their own young through associative learning as opposed to genetic cues, as shown by experiments in which Siberian jays did not differentiate between own and fostered offspring.
Breeding
Siberian Jays are strictly monogamous, with an established pair staying together and holding the same territory for life. Mate guarding in both sexes has been observed, whereby males and females become increasingly aggressive toward same-sex conspecifics.Ruth L. 2016. Mate-guarding in the Siberian jay (Perisoreus infaustus). Biology Independent Research Project, Karlstads Universitet. This may prevent extra-pair mating opportunities for the partner and thereby preserve inclusive fitness for both pair members. The size of the territory is , which is slightly enlarged in autumn and winter. 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. Widowed individuals have been observed to establish new pair bonds.
The nest is situated in a pine or spruce tree above ground within dense foliage for optimal concealment from nest predators. The nest comprises 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; which serves as necessary insulation against the extreme winter cold. Nest material is hoarded in winter long before building takes place. Nest building proper begins in late March and lasts for about three weeks. Both partners collect nest material; but only the female builds the nest.
The eggs are pale green, blue or grey and spotted with grey and brown. The average size is .Harrison C. 1975. A Field Guide to the Nests, Eggs and Nestlings of British and European Birds. London They are laid 31 March – 22 April, with a variable clutch size of 1–5 and an incubation period of about 19 days. The eggs are incubated entirely by the female, whilst the male provides all the food for the brooding female and the chicks.Eggers S. 2002. Behaviour and life-history responses to chick provisioning under the risk of nest predation. PhD dissertation, Uppsala University. The Siberian jay is single brooded and does not relay in a breeding season even after nest failure, but will wait until next year. A new nest is also built for every breeding attempt. Newly hatched young are almost bare and are closely covered by the female. Juveniles look similar to adults, but have paler heads.
A high proportion of the young's diet comprises insect larvae, which the male collects and stored in his oesophagus until he returns to the nest to regurgitate it and feed it to the young. In the first week of brooding, the male provides all the food for the female and young, but the female takes an increasing share of the work thereafter.