The Mexican Jay, formerly known as the Gray-breasted Jay, inhabits pine-oak-juniper woodland in the mountains of central and northern Mexico as far north as the mountain isolates ("sky islands") of Arizona, New Mexico, and western Texas. This highly social species defends permanent territories with groups of 5 to 25 individuals and has a social organization that is one of the most complex known for birds. Within each territory, one to four females may breed simultaneously and somewhat monogamously. The young are fed not only by their own parents but also by many other flock members, namely other breeders, failed breeders, and some nonbreeders.
The Mexican Jay does not migrate and has little or no dispersal from its natal group, probably being as extreme in this respect as any North American bird. It may live up to 20 years, often in the company of its offspring, parents, siblings, and other relatives on the territory where it was hatched or on an adjacent one. Flocks rely on pine nut and acorn crops to survive the winter.
Most of what is known about the behavior of this species comes from research on a color-banded population that has been studied every year for 37 years (1969¿2006) at the Southwestern Research Station (SWRS), in the Chiricahua Mountains of southeastern Arizona. Studies of a population in the Sierra del Carmen of northern Coahuila, Mexico, have recently contributed information from a group of jays that is divergent genetically, phenotypically, and behaviorally.
Early studies of Mexican Jays in Arizona focused on descriptions of the breeding system (Gross 1949, Brown 1963, 1970) including genealogies of family groups (Brown and Brown 1981). Later studies have explored the effect of climate (Brown and Li 1999) and climate change (Brown et al. 1999) on breeding; dominance (Barkan et al. 1986) and its effects on breeding (Brown et al. 1997) and foraging interactions (McCormack et al. 2007); hormonal correlates of helping behavior (Brown and Vleck 1998; Vleck and Brown 1999); and vocal recognition among group members (Hopp et al. 2001). As with many bird species formerly considered monogamous, high rates of extra-pair fertilization have been detected through the use of genetic techniques (Bowen et al. 1995; Li and Brown 2000; Eimes et al 2005).
The Mexican Jay has also been used in laboratory studies comparing spatial memory in seed-caching corvids. They possess modest cache-recovery skills compared to more highly specialized seed-eating species (Bednekoff and Balda 1996; Bednekoff et al, 1997). Other recent studies have recognized Aphelocoma jays in general, and Mexican jays specifically, as being labile in their ecological niche, with implications for speciation (Peterson and Burt 1992; Rice et al. 2003; McCormack et al. 2008a). Their sedentary ways make them amenable to studies of genetic differentiation at both large and small spatial scales (McCormack et al. 2008a, b).
While Mexican jays have for some time been considered a single species with seven subspecies, they have often been organized into three groups, and recent molecular and morphological analysis argues in favor of splitting Mexican jays into two or more species. This idea is not entirely without precedent, as the subspecies were originally (Pitelka 1951) placed into three groups corresponding to the Sierra Madre Oriental, Sierra Madre Occidental, and the Transvolcanic Belt (also sometimes referred to Orientalis, Occidentalis, and Transvolcanica). A proposed alternate taxonomy for Mexican birds (Navarro-Sigüenza and Peterson 2004) elevates these groups to species level (A. wollweberi, A. potosina, and A. ultramarina) based on genetic distance (Peterson 1990; Peterson 1992).
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