The highly variable Red-tailed Hawk Buteo jamaicensis (Gmelin) of North America has been a thorn in the side of many taxonomists. The Red-tail in North America is divided into six subspecies of races, three color phases, and is very susceptible to albinism and melanism. Measurements vary by age, sex, and race, and immature and subadult plumages vary in a gradual or prolonged change from juvenile to adult. These factors, plus the individuals from the zones of intergraduation, impose a very trying problem, of identification. However, the principal factor involved is in the plumage characteristics and variation of the geographical races.