113 BULLETIN OF THE 



but they more or less mix up during winter, and specimens are of fre- 

 quent occurrence that, from their not being referable to either form, have 

 been assigned to the series of " hybrids.'" J. caniceps is the most strong- 

 ly marked form, in its having the middle of the back reddish, forming 

 a restricted, well-defined patch. J. oregonus has the back also reddish, 

 this color occupying a larger area than in J. caniceps, more diffused, 

 and involving the secondaries ; but its extent and intensity varies greatly 

 in different individuals. The sides are also tinged with a pinkish rufous 

 tint, and the slate of the anterior half of the body is darker than in the 

 other. J. hyemalis has the rufous tint present only in young or au- 

 tumnal specimens, which sometimes strongly approach J. oregonus. J. 

 oregonus, on the one hand, inosculates with J. caniceps, and on the 

 other, with J. hyemalis; caniceps and oregonus both apparently merg- 

 ing into J. cinereus of Mexico, through the scarcely distinguishable 

 J. dorsalis. Melospiza melodia is represented in the interior by a race 

 (JLfallax) paler than the eastern, and on the Pacific coast by a darker 

 race, which again divides into a northern (M. insignis) and a southern 

 (JL Heermanni et Gouldii, etc.), all of which so intergrade as to be but 

 unsatisfactorily definable, though in their extreme stages they present 

 strong points of difference. Few congeneric species, it would seem, 

 need be more distinct than Colaptes auratus and G. mexicanus, the one 

 occupying the eastern and the other the western side of the continent. 

 Yet a mixed race has been long known to exist in the region where their 

 habitats adjoin, in which every possible combination of the characters 

 of the two birds is presented, and which shade off gradually on the one 

 side into C. auratus, and on the other into C. mexicanus ; these, as it 

 were, engrafted characters not entirely fading out in either direction for 

 a distance of several hundred miles; while to the southwestward is a 

 smaller synthetic race (C. chrgsoides) partaking mainly of the charac- 

 ters of O. auratus. 



"When but comparatively few instances were known, in which speci- 

 mens combined in various degrees the characters of two quite distinct 

 species, their synthetic character was generally explained by the theory 

 of hybridity ; but the irrefragibility of the evidence now at hand in 

 proof of the gradual intergradation of such forms over large areas, — the 

 transition being so gradual as to occupy hundreds of miles in the pas- 

 sage, — and also coincident with a similarly gradual change in the con- 

 ditions of environment, together with the demonstrable evidence of the 



