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Mar., 1910 HABITS OF THE BLACK CAPT VIREO 71 however, includes only one adult female (there are eighteen adult males) if the sex has been correctly determined in all cases, shows that the sexes are alike and that the presence of black on the head or its extent is probably a matter of age. The grayer headed specimens invariably have the ?vhites of the under parts less pure, in this respect being more or less like young birds in their first autumn which lends probability to the theory that the relative age is the true explanation of the varia- tions noted." As for myself, however, I think that Mr. Ridsway lackt sufficient material for examination, and has been led astray by the mistakes of collectors in determining the sex correctly in some of the specimens. I spent three weeks with the Black- caps at their breeding time, when they were in full plumage, and had ample time and opportunity to study them. I watcht them build their nests, incubate their eggs and feed their yotmg. I dis- sected over thirty of them, and can say that the sexes are nol alike, and that the female does no! have a distinct black cap at any age. This matter, as to whether the sexes of Vireo alricapillus are differ- ent in plumage or not, has been disoust by several writers since the year 1878, and both conclusions have been reacht. For several years I have been of the opinion that the sexes are different, and after an ex- amination of nearly forty skins I am firmly convinced that such is the case. The material on which I base the following conclusions numbers nineteen specimens, six adult males taken in July 1901, seven adult males and five adult females in May, Fig. 24. DORSAL SURFACE OF MALE AND FEI?IALE BLACK 1902, all taken in Blaine CAPT VIREO, ILLUSTRATING SEXUAL DIFFERENCES IN COLORATION AND MAKINGS County, Oklahoma; and. one adult male taken in Comanche County, Kansas, in May, 1885. When compared with the males, it is at once apparent that the females have a distinct buffy tinge on the under parts, strongest on the breast, and nearly, ? not entirely, absent from the throat and abdomen. Above, the olive-green tint6f the back averages duller in color than in the males, tho this character is not strongl?y noticeable in some instances. The wing bars and the light edgings to the tertials are also paler---nearly white--in place of the yellow of the males. The same is true, to a less extent, of the light greenish edgings of the rectrices. In the males the head and neck--except the throat, loral streak, and an orbital ring of white ---are clear black, while the same region in the females is slate-gray. (See Fig. 24.) The white of the loral and orbital region is clearer in the real% tho