264 BULLETIN 17 6, UNITED STATES NATIONAL MUSEUM 



that in "the third year the color is black, with a very faint edging of 

 white on under tail coverts." There is great individual variation in 

 the amount of white on the under parts of immature birds, probably 

 due to wear or earlier or later molting in different individuals. It 

 seems fair to assume that the "very faint edging" referred to by Mr. 

 Drew may be only evidence of further advance in second-year birds. 

 Apparentl}^ these swifts molt their contour plumage, perhaps their 

 wings and tails, during the early summer, Mr. Rathbun tells me that 

 he has always noticed that summer specimens "appear to have almost 

 fresh plumage"; and Harry S. Swarth (1922) says that the birds he 

 collected in the Stikine region, between August 19 and 30, "had en- 

 tirely finished the annual molt and were all in the new plumage." 



In the adult plumage the sexes are very much alike in coloration, 

 though females average somewhat paler and browner on the under 

 parts, and the female tail is not so deeply emarginate as that of the 

 male. Mr. Drew (1882) says that in the adult the outer tail feathers 

 are three-eighths of an inch longer than the inner feathers, giving the 

 tail a forked appearance; this is undoubtedly true of fully adult 

 males, and perhaps of some very old females. Mr. Rathbun tells me 

 that he can usually distinguish the two sexes in flight by the extent 

 to which the tail is emarginated. In the series that I have examined 

 all the young white-spotted birds have square or slightly emarginate 

 tails, all the adult males have deeply emarginate tails, and all 

 the adult females have only slightly emarginate tails. Major 

 Brooks, who probably has handled more black swifts than anyone 

 in North America, wrote to Mr. Rathbun: "Swarth and myself, to- 

 gether with another observer in the last century, have carefully 

 recorded that some females, probably about 10 percent, are absolutely 

 indistinguishable from the adult male in every external character, 

 emargination of tail, absence of white spots, etc." In a series of black 

 swifts, collected by Mr. Swarth (1912) in southeastern Alaska in June 

 and July 1909, "there is one female that in color and markings is 

 indistinguishable from the males. * * * Like the others, however, 

 it differs from the males in having a square, rather than a forked 

 tail." This particular female contained an egg, almost ready to be 

 laid, so that there was no doubt about the sex. 



Mr. Rathbun (1925) writes: "The males are larger and darker 

 than the females. As a rule their sooty underparts from the breast 

 down lack any trace of light tipping on the feathers, and when this 

 does occur the tips are of a brownish tint and very faint. In all 

 our males the under tail coverts are tipped with brownish, rather 

 well defined though much obscured in some individuals. There is a 

 larse variation in the amount of hoariness on the forehead." 



