... which is only 9 3/4 inches (adult). The Chukar is 14-inch (adult). The only similar bird in size/shape would be the Gray Partridge, but different coloring.

More than likely for the choice of the Northern Bobwhite on the chip is that is strikingly unmistakable; nothing comes close to it... Thus USPC being a leader in perfection, I'll bet 50-cents it's a Northern Bobwhite.