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Western Scrub-Jay
Aphelocoma californica
Order
PASSERIFORMES
– Family
CORVIDAE
Authors: Curry, Robert L., A. Townsend Peterson, and Tom A. Langen

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Introduction

Adult Western Scrub-Jay
Figure 1. Distribution of the Western Scrub-Jay.

Throughout the American West, and through arid regions of Mexico, the Western Scrub-Jay is the familiar jay of a broad range of lowland and montane habitats. The species frequents scrub and dry woodlands dominated by oaks or piñon pines, but has also adapted well to suburban landscapes. Western Scrub-Jays come into contact with several related species, including the crested Steller’s Jay (Cyanocitta stelleri) at higher elevations from Colorado and Washington southward and Blue Jay (C. cristata) in the southern Great Plains to the east. Western Scrub-Jays overlap with Mexican Jays (A. ultramarina) in hills and mountains from Arizona and New Mexico through both cordilleras of central Mexico, and in the state of Veracruz these 2 species are joined by the congeneric Unicolored Jay (A. unicolor; Pitelka 1951). While the Western Scrub-Jay’s broad diet of mainly arthropods and nuts is similar to those of its sympatric relatives, it tends to frequent drier, hotter, and more open habitat and is typically found at lower elevations than the other species.

Across the broad geographic range of the Western Scrub-Jay, variation in physical appearance is considerable and has been the subject of frequent study (Pitelka 1951, 1961; Peterson 1990a, 1991b, 1991c; 1992, 1993; Peterson and Burt 1992, Peterson and Vargas B. 1993; Bardwell et al. 2001). Birds in interior populations are paler and more shy than coastal birds, which are darker in color and more bold in behavior. Overlaying the preceding pattern is substantial variation in bill morphology that reflects differences in diet. Along the Pacific Coast, birds in northern parts of the range also are generally larger than their southern counterparts, with the smallest Western Scrub-Jays living on the Baja Peninsula; jays in the interior of Mexico, however, are among the largest of the species overall. Differentiation is sufficiently great that the division of the West-ern Scrub-Jay into 3 distinct species may be justified.

Variation within the Western Scrub-Jay represents a subset of the variation that extends to its 2 closest relatives, the Island Scrub-Jay (A. insularis) and the Florida Scrub-Jay (A. coerulescens). The former, a peripheral population derivative of West Coast populations of the Western Scrub-Jay, is distinguished by its restricted geographic range (endemic to Santa Cruz Island, California), dramatically larger size, and more intensely bright blue-and-white plumage (Pitelka 1951; Atwood 1978, 1979, 1980a, 1980b; Atwood et al. 1990; Collins and Corey 1994; Curry and Delaney 2002). The smaller Florida Scrub-Jay is an even more clearly separated form, likely having branched off from the rest of the group during periods in the Pleistocene when climatic changes first supported—and later severed—a swath of arid terrain along the Gulf of Mexico coastline. Intensive study over more than 3 decades has emphasized the cooperative breeding social organization of the endemic Florida population (Woolfenden and Fitzpatrick 1984, 1996). Accumulated evidence from numerous but less intensive field studies of breeding biology and demography of the Western Scrub-Jay has presented a general picture of a less social, non-cooperative species (Ritter 1972, 1983, 1984; Verbeek 1973; Carmen 1988, in press). However, the discovery of helpers at the nest among Western Scrub-Jays in a Mexican population (Peterson and Burt 1992, Burt and Peterson 1993) has shown that the dichotomy is not as dramatic as was once thought.

Along with being a model species for studies on morphological and behavioral evolution, the Western Scrub-Jay has become 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; Clayton et al. 2000, 2001; Emery and Clayton 2001a, 2001b). While less remarkable at storing and recovering food items than some other members of the Corvidae, such as the Clark’s Nutcracker (Nucifraga columbiana), the Western Scrub-Jay nevertheless exhibits impressive skills in locating and selecting food and in dealing adaptively with social competition from other jays (Langen 1999; Clayton et al. 2000, 2001; Emery and Clayton 2001a, 2001b).

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 Western Scrub-Jay promises to play an important ongoing role in efforts to understand the ecological and evolutionary factors affecting not just corvids, but all birds.