_Breeding range._--The Socorro warbler is known to breed only on Socorro Island, where it is resident. It has been found in the breeding season near Todos Santos, Baja California. This warbler has been found in winter in two localities (Todos Santos and El Oro) in Baja California, and appears to be resident in small numbers. PEUCEDRAMUS TAENIATUS ARIZONAE Miller and Griscom NORTHERN OLIVE WARBLER PLATE 23 HABITS The olive warbler was long classed as a species of _Dendroica_, with _Peucedramus_ regarded as a subgenus, but it is now properly placed in a genus by itself, for as Dr. Chapman (1907) points out it differs from _Dendroica_ chiefly "in its slenderer, more rounded bill, proportionately longer wings (about 1.00 inch longer than the tail) and decidedly forked tail, the central tail feathers being more than .25 inches shorter than the other ones. In general color and pattern of coloration _Peucedramus_ is markedly unlike _Dendroica_, from all the species of which the male differs in requiring two years to acquire adult plumage." For a still longer time it was supposed to be a homogeneous species, until Miller and Griscom (1925) made a study of it and divided the species into five subspecies, mostly Mexican and Central American. In giving this bird the name _P. t. arizonae_, they state that it is entirely different in coloration from the type race; "upperparts plain mouse-gray, in spring plumage almost never tinged with olivaceous, even on the upper tail-coverts, appearing lighter and grayer than typical _olivaceus_; collar on hind neck not so complete, usually invading the occiput; primaries rarely if ever edged with olive-green in spring plumage; head and throat plain ochraceous, duller than in typical _olivaceus_; underparts lighter, the center of the belly purer white, more contrasted with the flanks, which are less olivaceous, more grayish brown; size as in typical _olivaceus_. Throat and side of neck of adult female and immature pale lemon-yellow." They give as its range "mountains of southern and central Arizona south at least to Chihuahua and perhaps east to western Tamaulipas (Miquihuana)." The species had long been known in Mexico and had been erroneously reported in Texas, but it remained for Henry W. Henshaw (1875) to record it definitely as a North American bird by capturing three specimens on Mount Graham, Ariz., in September, 1874. Since then it has been noted by numerous observers on several other mountain ranges in southern Arizona, where it is now known to be fairly common in summer and where a few remain in winter.