#R, Zacatecas, Mexico; restricted to Valparaíso Mountains.
Until recently considered conspecific with A. ultramarina, but molecular evidence#R points to a split, and this is just supported by relatively understated phenotypic characters: differs in its paler blue upperparts, with blue on crown extending less far onto mantle (2); slightly less pronounced vague streaking on throat (1); rather smaller size (effect size for tail length in males −2.4, score 2); slightly shorter call in W taxa (arizonae, nominate; proposed W Mexican form gracilis subsumed into latter) (1) with slightly higher minimum frequency (1); and considerably shorter call in E taxa (couchii, potosina) (2) with notably lower minimum frequency (2)#R. Difference in call of E taxa, which are rather smaller and genetically fairly distinct, presumably reflects their unique possession of “rattle call”#R. Races represent three groups, otherwise differing mainly in depth of colouration and in size. Nominate wollweberi intergrades with arizonae to N. Four subspecies recognized.
28–32 cm; male 84–150 g, female 77–137 g. Small, chunky, crestless jay, dull bluish above and dingy below, with fairly heavy, pointed bill; bill length varies significantly with season, shorter in winter. Nominate race has head dark bluish, lores black, upperparts more bluish purple; brownish grey below, throat and undertail-coverts paler; iris brown; bill and legs black. Sexes similar, male slightly larger than female. Juvenile differs from adult in being mostly mouse-grey above with hint of dull blue wash, tail grey to blue-green and duller, wings greyer with distal portions dark brown, legs brown, gradually deepening to black, bill typically pale; first-year in autumn slightly smaller (especially in wings and tail) than adult, with duller plumage, juvenile tail retained until definitive moult complete (c. 12 months after hatching). Races differ mainly in depth of coloration and in size: potosina is duller and smaller than nominate; arizonae is deep dull blue above, facial region dull but darker blue, back brownish grey with dull blue elements, rump more blue than black, uppertailc-overts light dull blue, primaries with dull dark brown tips, chest light brownish grey with some dull blue cast (obscure broad band from sides of neck across upper chest), belly and undertail-coverts white; nominate is smaller than previous, bluer above, has lighter underparts, juvenile browner-backed; gracilis is lighter in colour and smaller than last, strikingly smaller than arizonae with back darker and less blue, underparts lighter with little or no blue wash; couchii is smaller than arizonae, has darker back, darker and more intensely blue neck and head with stronger contrast between neck and back, lighter throat contrasting more with brown-grey breast, blue (rather than brownish-grey) wash on lower breast and belly, juvenile overall darker and browner with less grey.
ssp wollweberi Arizona Jay
ssp couchii Monterrey Jay
ssp potosina San Luis Potosi Jay
Not formally studied. Like other corvids, has soft “whisper-song”, begging calls, and “rattle”. Whisper-song given by male during courtship and by lone individuals; only female thought to “rattle”; young and subordinate birds, including breeding females, beg from parents, mates and dominant flock members. “Loud call” by flock-members when encountering trespassing jays, stationary predators, and generally when scolding in agitated manner; softer version, “hawk buzz”, given to accipiters and other flying raptors.
Montane mixed woodland with oak (Quercus) and pine (Pinus) or juniper (Juniperus); at lower elevations found along creeks and grasslands with oak-dominated riparian woods. Nominate found at c. 1460–2100 m elevation; couchii at 880–3000 m. Reliant on the acorns or large seeds of piñon pine that occur throughout these habitat types.
Food and feeding
Omnivorous; seasonal specialist on pine and oak crops. Diet nuts, fruits, seeds, nectar; invertebrates; small vertebrates, e.g. lizards, small birds and nest contents (including those of own species); two observations of predation on small bats in Arizona#R. Takes carrion and, where available, scraps provided by humans. Cached nuts eaten throughout winter and early spring, even by incubating female. Opens acorns and pine seeds by forceful pounding and tearing; experimental evidence suggests ability to determine nut quality#R; bill morphology reflects diet at local scale (those eating pine seeds have long, unhooked bill, acorn-eaters have stouter, hooked bill). Lives in small, permanent flocks of 2–25 individuals. Stores food throughout year, especially Jul–Aug, when acorns and pine seeds harvested and cached singly throughout group’s territory. Caches 1000s of pine seeds and acorns per autumn, in 100s of locations; in each trip from harvest to caching grounds, transports up to five seeds in mouth or bill a short distance (1–500 m); individual uses spatial memory to recover seeds cached by itself and those seen cached by others. Feeds primarily on ground for insects and stored nuts, and in shrubs and tree canopy and on trunks for fruits, seeds, nectar and invertebrates.
Nestbuilding begins late Feb and early Mar, and laying late Mar to early Apr (rarely through Jun) in S USA (Arizona); repeated nesting after failure. Variety of social bonds formed among males and females, which live together in groups and communally defend all-purpose territory; territories exclusive property of group, and stable in size and location for decades; within flock, males compete for mates and females compete over nests. Extremely complex breeding system varies from monogamous (most situations) to polygynandrous (with multiple breeding males and breeding females in one social group), exclusive pair-bond rare; each female guarded by a male, which (if dominant over other males) sires most or all young in her nest, but multiple paternity of a clutch frequent, and ability to obtain extra-pair fertilizations favours subordinate males, which may remain in natal flock as helpers; rarely, two females lay in a single nest and share incubation. Male typically initiates nest construction and may select nest-site, female may also “approve” site, usually only single male and female build nest, but several nests initiated simultaneously by male-female pairs within group; in Arizona, bulky nest had coarse outer platform 330 mm in diameter and 76 mm deep, constructed of dead twigs, rootlets woven into coarse outer sticks, inner cup (127 mm × 51 mm) lined with fibres from shredded yucca (Yucca) leaves and animal hair (material often stolen from other pairs within territory during building process), placed 3·7–24·4 m above ground and well concealed in leafy tree; entire nests of subordinate pairs may be usurped by dominant pairs. Clutch 1–5 eggs (typically 4–5), colour pale green to pale blue, with varying amounts of speckling and blotching; eggs of couchii at high elevations have more green and blue pigment than those at lower elevations#R; incubation by female, fed throughout by guarding male and most other group-members (excluding other breeding females), period 18 days; chicks brooded by incubating female, fed by all group-members, nestling period 24–28 days; juveniles continue to be fed for several weeks after fledging, and most spend entire life in natal flock, often breeding in company of parents and siblings. In Arizona success typically high, each female produced on average 1·4 fledglings per year (older breeders more successful than inexperienced ones), and lifetime reproductive success of females 8·7 fledglings (range 0–50); females may continue to experience improved pairing and egg-laying success at age eight years and above; birds nesting early in year in Arizona produced more nestlings, yearlings and three-year-olds. Recorded longevity 21 years in wild; in Arizona, annual survival rate of individuals at least one year old was 81%.
Resident. Dispersal extremely limited, but rare long-distance movements and wanderings of vagrants to unusually low or high elevations have been documented; one record in S Kansas (SC USA). Some wander from territory in harsh winters.
Status and conservation
Not globally threatened (Least Concern). Common throughout range; global population estimate 2 million individuals. In Arizona, average size of home range 0·36 km². Populations in Arizona fluctuated annually during 1986–1994, but no constant increase or decrease. In Mexico, race potosina (on C plateau) is at risk because it occurs in small area undergoing extensive habitat clearance for agriculture and timber. Throughout its range, this species is vulnerable to exotic and increasingly common diseases, including West Nile Virus, which is deadly to most corvids, and Sudden Oak Death; also to loss of pinyon pine woodlands to drought and fungus, which can reduce oak and pine mast.
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