blue. On the other hand, Mexican jays in Arizona - also arid habitat - have a washed-out appearance, in accordance with Gloger's rule. Western group Sierra Madre Occidental in northern [Jalisco] north to central Arizona and southwestern New Mexico. Southern and eastern limits in Jalisco deserve further study. Juveniles have a pink/pale base to the otherwise black bill for up to two years. Eggs are pale green-blue and unspeckled, unlike Eastern group where speckled eggs are common. Aphelocoma wollweberi gracilis Eastern Nayarit and northern Jalisco Smallest of the Western subspecies with a distinct, high-pitched vocalization. Aphelocoma wollweberi wollweberi Durango and Zacatecas Intermediate in size. Aphelocoma wollweberi arizonae Sonora and Chihuahua north to Arizona and New Mexico, United States Largest and palest of all the subspecies. Eastern group Sierra Madre Oriental in Nuevo León and western Tamaulipas north to Texas (Chisos Mountains). Juveniles have an all-black exterior to the bill after fledging, but roof of inner upper mandible can remain partially white for up to two years. Reports of less social behavior compared to other groups are over-stated and credible accounts of cooperative breeding (Ligon and Husar 1974) and large flock sizes (Bhagabati and Horvath 2006) exist. Plain, speckled, and even white eggs have been observed in a single study area (McCormack and Berg 2010). Aphelocoma wollweberi couchii Smaller than preceding. Population of the latter subspecies distinguishable by more contrasting markings and ecological preferences (lowland birds). Egg color may range from plain blue to Nile blue with pale brownish speckling, most heavy on blunt half. Gives rattle call similar to Cyanocitta and other Aphelocoma jays. Central Plateau group Central Plateau in Queretaro, Guanajuato, San Luis Potosi, and eastern Jalisco. Similar to Eastern group but larger in most features. Distinguishable in morphology and plumage in ~80% of specimens. There is an area of apparent hybridization in San Luis Potosi that deserves study. Aphelocoma wollweberi potosina Description The Mexican jay is a medium-large (~120 g) passerine similar in size to most other jays, with a blue head, blue-gray mantle, blue wings and tail, and pale gray breast and underparts. The sexes are morphologically similar, and juveniles differ only in having less blue coloration and, in some populations, a pink/pale (instead of black) bill that progressively becomes more black with age (Brown and Horvath 1989). Some field guides misreport this color as yellow because the pale bill becomes yellow in museum study skins. The