Editor’s Note (Aug. 2016): This species is the result of a recent taxonomic split. Maps, rich media, and Introduction, Appearance, and Systematics articles have been updated. Other articles are being edited and may reflect content from the original Western Scrub-Jay account.
Throughout much of the American Southwest and mainland portions of Mexico, Woodhouse’s Scrub-Jay is the familiar jay within a range of lowland and montane habitats. This species is a recent taxonomic split of the Western Scrub-Jay (Aphelocoma californica) complex that resulted in recognition of the Woodhouse’s Scrub-Jay (A. woodhouseii) and California Scrub-Jay (A. californica) (Chesser et al. 2016), the latter occurring in coastal states from Washington to California, south to the southern tip of Baja California.
Beyond their different geographic ranges, Woodhouse’s Scrub-Jays occupy dry, open scrub and woodland, especially piñon-juniper, whereas California Scrub-Jays are primarily found in oak woodland and scrub habitats; both species have adapted well to suburban landscapes. Woodhouse’s Scrub-Jay differs outwardly from the California Scrub-Jay by having duller blue upperparts, grayer underparts, and a breast-band that is paler and less distinct. It has a thinner, straighter bill that is less hooked than that of the California Scrub-Jay ( Pitelka 1951d ), and these differences in bill shape may be adaptations to food resources in their different habitats ( Peterson 1993 , Bardwell et al. 2001 ). Further, the two species exhibit differences in behavior and vocalizations ( Dunn and Garrett 2001 , ). For example, the calls of Woodhouse’s Scrub-Jay are typically 2-syllabled and higher pitched than the harsher, 1-syllabled and lower-pitched notes of the California Scrub-Jay ( Dunn and Garrett 2001 ).
Woodhouse’s Scrub-Jay includes 7 subspecies ( American Ornithologists' Union 1957 ) in two groups (Chesser et al. 2016), a Great Basin group and a Southern Mexico group with 2 subspecies that are sometimes treated as a separate species (Sumichrast’s Jay) ( Peterson 1992a , Peterson and Navarro-Siguenza 1999 , ). Woodhouse’s Scrub-Jay is sister to a clade that contains the California Scrub-Jay and the Island Scrub-Jay (A. insularis), endemic to Santa Cruz Island, California ( Peterson 1990b , Peterson 1992a , McCormack et al. 2011). Woodhouse’s and California scrub-jays have few or no fixed differences in alleles and interbreed where their geographic ranges contact in western Nevada and east-central California, and in desert ranges of eastern California ( Peterson 1990a , Peterson 1990b , Peterson 1992a ). Despite this ongoing gene flow, the hybrid zone is narrow, and there is evidence for selection against hybrids (Gowen et al. 2014).
This species is less social than other jays and largely not a cooperative breeder; one exception involves southern Mexico populations, where helpers at the nest have been documented ( Peterson and Burt 1992 , Burt and Peterson 1993 ). This provides some support for the notion that Sumichrast’s Jay may be a separate species.
The Woodhouse’s Scrub-Jay is well known among animal behaviorists as a model subject in studies of foraging behavior and cognitive abilities, including spatial memory ( Vander Wall and Balda 1981 , Balda and Kamil 1989 , Kamil et al. 1994 , Balda et al. 1997 , Bednekoff et al. 1997 ). Although less remarkable at storing and recovering food items than corvids, like the Clark's Nutcracker (Nucifraga columbiana), Woodhouse’s Scrub-Jay nevertheless exhibits impressive skills in locating and selecting food.
The complexity of morphological and behavioral patterns within this common and broadly distributed species continues to pose challenging questions for ornithologists. Along with its close relatives, the Woodhouse’s Scrub-Jay plays an important ongoing role in efforts to understand the ecological and evolutionary forces affecting not just corvids, but all birds.