Among the more difficult bird-identification problems in western North America—at least in Oregon, California, and northern Baja California—is how to distinguish the Red-winged Blackbird (Agelaius phoeniceus) and Tricolored Blackbird (A. tricolor), especially females. None of the major field guides covers the problem thoroughly. The National Geographic Society guide covers the issue best in text, but in no guide are there illustrations of the difference wrought by the most critical factor: feather wear.