Mexican Jay

The Mexican jay used to be known as the gray-breasted jay. It has a blue head, blue-gray mantle (between the neck and the rump), blue wings and tail, a pale gray breast and underparts and a black bill and legs. It differs from the western scrub jay by its plain (unstreaked) breast and throat and its mantle contrasting less with its head and wings. 

This photo gives a good look at the mantle (the back, or area between the neck and rump) which is blue-gray, compared to the blue of the head and wings. 

This photo gives a good look at the pale gray underparts and breast. 

A more frontal look at the breast. 

There are five subspecies and three major groupings. The western group is found in the Sierra Madre Occidental, a mountain system that runs along the east side of the Gulf of California. This group is also found up through central Arizona and southwestern New Mexico. The eastern group is found in the Sierra Madre Oriental, a mountain range that runs along the Gulf of Mexico and slants upward as far as the Big Bend of Texas, where it is found in the Chisos Mountains of Big Bend National Park. The Central Plateau group, also known as the Mexican Altiplano, is found in the plateau that occupies much of central and northern Mexico between the eastern group and western group. The differences between the groups relate to things like the color of their eggs and bills in juvenile birds. 

A map from Wikipedia showing the Sierra Madre Occidental, Sierra Madre Oriental and Central Plateau (Altiplano). 

These Mexican jays are part of the eastern group which we saw in the Chisos Mountains of Big Bend National Park in southwestern Texas. There are several different jays although we saw them all in the same place.