1907] Beebe: Geographic Variation in Birds. 23 



locality, except Guatemala (2), Honduras-Nicaragua (1) and 

 Brazil (1). But even with this unequal distribution the results 

 of the various measurements are consistent and serve perfectly 

 to demonstrate what I. desire, namely, distributional variation in 

 these wild birds.* 



In the case of the dark, distal primary patch, which is shut 

 off from the rest of the feather by the succeeding chestnut, there 

 is a gradual decrease from Arizona to Nicaragua, indicative of 

 the corresponding increase of chestnut. In Venezuelan and Bra- 

 zilian specimens is found a sudden and extensive decrease of 

 the chestnut ; in fact, in the narrow outer side of the vane of the 

 primaries this color is almost, in the Venezuelan doves, or 

 wholly, in the Brazilian birds, lacking. 



The white tip of the outer, or sixth, pair of rectrices shows 

 a gradual increase in area southward, from 39.2 mm. in Arizona 

 to 49.2 mm. in Nicaragua. The widest break is between Guate- 

 malan and Honduras birds, being 3.5 mm. In South American 

 birds a considerable reduction occurs — almost to the level of the 

 extreme northern specimens. 



The variation in the white of the fourth pair of tail feath- 

 ers is peculiar. From Arizona to Central Mexico there is a slight 

 but gradual reduction in area — from 16.1 in the north to 13.9 

 in the latter locality. The Guatemalan, Nicaraguan and Venezu- 

 elan birds show a sudden increase — to 25.8, 30.6 and 36.2 mm. 

 respectively, showing that in this pair of rectrices the color va- 

 riation is far more active and more significant of distribution, 

 and hence climatal effect, than in the outer, or sixth, pair. The 

 size of the white spots in the Brazilian specimen, 24.8 mm., is 

 interesting when we see how closely it approaches the Guate- 

 malan birds, and consider that the two localities, Guatemala and 

 Bahia, Brazil, are about 15 degrees distant from the equator, the 

 one north, the other south, latitude. 



The status of variation in the fourth pair is duplicated in 

 the third pair of rectrices, and is even more pronounced, as refer- 

 ence to Table IV will show. The first important fact (as demon- 

 strated by the lessened number of specimens in this Table) is 

 that in two-thirds of the doves from Arizona to Mexico the 

 white tips of the third pair of tail feathers are entirely absent, 

 the proximal brown color extending unbroken to the very ex- 

 tremity of the feathers. Even where the white color is present 

 it is but a terminal fringe, varying in average area from 1 mm. 

 to 2.9 mm. From Guatemala southward, to and including the 



* For the use of fifty-six skins of Seardafella, I am indebted to the American Museum 

 of Natural History, and for the type specimen of <S'. i. dialeueos to Mr. Outram Bangs. 



