_Field marks._--In general appearance and behavior the olive warbler suggests the pine warbler, especially as it creeps over the pines. The orange-brown head, neck, and breast of the adult male, with the conspicuous black band through the eye, is distinctive; these colors are much paler and more yellowish in the female, and the band through the eye is grayish. Both adults have two white wing bars, a white area at the base of the primaries and much white in the tail, the white areas being more restricted in the female. Young birds are much like the female (see descriptions of plumages). _Winter._--The olive warbler, as a species, is probably permanently resident throughout most of its Mexican and Central American range. But the northern olive warbler is evidently partially migratory, though some individuals, perhaps many, remain in Arizona during part, or all, of the winter. All of the 15 specimens taken by Stephens for William Brewster (1882b) were collected in March, probably too early to be migrants, and he says that Stephens had previously taken one in February 1880, evidently a wintering bird. Mr. Swarth (1904) writes: "I have not found this species very abundant in the Huachucas at any time, but it is probably resident to some extent, for I secured an adult male on February 21 when the snow was deep on the ground. During March I saw several more, all adult males and single birds, usually with a troop of Pygmy Nuthatches; but it was not until the first of April, when the other warblers were arriving, that they became at all abundant." Scott (1885) found them on the Catalinas under winter conditions, with snow on the ground, and says: "I think there can be little if any doubt that they are residents all the year." And Dr. W. P. Taylor (MS.) took one in the Santa Ritas on February 4, 1923. Just how far south go the birds that migrate away from Arizona does not seem to be known, but apparently they have not been detected beyond Chihuahua and Tamaulipas. Perhaps they do not migrate at all. DISTRIBUTION _Range._--Southwestern United States to northern Nicaragua. _Breeding range._--The northern olive warbler breeds =north= to central Arizona (Baker's Butte and White Mountains) and central western New Mexico (Reserve). =East= to western New Mexico (Reserve and McKnight's Canyon); Chihuahua (Colonia García); southeastern Coahuila (Diamante Pass); and southwestern Tamaulipas (Miquihuana). =South= to southwestern Tamaulipas (Miquihuana) and southern Durango (Durango). =West= to Durango (Durango); Sonora (Sierra Saguaribo); and southeastern and central Arizona (Huachuca Mountains, Santa Catalina Mountains, and Baker's Butte). Other races occur in southern Mexico and Central America. _Winter range._--The northern olive warbler is probably migratory to some extent, individuals withdrawing to the southern part of the range, but it is found in winter occasionally or in small numbers as far north as southern Arizona.