8 NATURAL HISTORY OF BIRDS. 



the young plumage. Candor compels us to state, however, that the evidence for the 

 white and the colored birds being only phases is yet insufficient, the more so as geo- 

 graphical distribution seems to have something to do with the matter, for it is stated 

 that, in Florida, the white birds are confined mainly to the Atlantic coast, while the 

 colored ones chiefly inhabit the Gulf side. The example from the herons can be 

 nearly duplicated by the status of some forms of fulmars from the northern Atlantic 

 and Pacific oceans, although in this case the geographical distribution seems to lie a 

 moment of still greater importance, for I think I have proved that, in both oceans, the 

 dark phases are predominant to the westward. We have other examples of dichroma- 

 tism in the same group as the dark and the white form of Ossifraya yiyantea ; and 

 Mr. Ridgway's suggestion, that it will be found more extensively all through the super- 

 family of the Tubinares or Proeellaroideae, is well worth consideration. Dichroma- 

 tism among the owls, or erythrochroism, as it is here called, because of rufous being 

 the color producing one of the phases, is not uncommon, but seems to be still more 

 influenced by the geographical distribution, at least in our little screech owl (Mega- 

 scops asio), which, in the Mississippi Valley, has more rufous than gray individuals, in 

 the Atlantic states both phases nearly equally represented, while west of an'd includ- 

 ing the Rocky Mountains, only gray birds occur. Want of space compels us to pass 

 in silence many more examples, for instance, the white and the blue-winged snow- 

 geese, the dark and light-colored phases of many hawks (JButeones), but we cannot dis- 

 miss this matter without having mentioned that most perplexing question to American 

 ornithologists: What are the relations of the two forms of flickers (Cohiptes) and 

 their numerous intermediate individuals? The two flickers are mainly characterized 

 by the color of the under surface of the wing and tail feathers, these being red in the 

 red-shafted (Colaptes mexicanus), gamboge yellow in the yellow-shafted flicker (C. ax- 

 ratus), in addition to which the latter has a red nuchal crescent; besides, the males 

 are distinguished by having a malar stripe, which is red in the red-shafted species, but 

 black in the other; the former is chiefly a western bird, the latter inhabits the east and 

 the north. Hardly two species could look more distinct than the typical specimens of 

 these remarkable birds ; but the characters are mixed in every possible degree in the 

 individuals inhabiting the region intermediate between the two, to such an extent as 

 to be completely without parallel among birds. They were generally declared to be 

 hybrids until intermediate specimens were found in localities for example, Florida - 

 where only one of the typical species occur, and, consequently, hybridity is an impos- 

 sibility. Are they incipient species? are they local varieties? or what? As there are 

 no structural characters involved, the question is merely one of color ; why then not 

 seek refuge in l dichromatism ' or rather ' trichromatism,' affected by geographical dis- 

 tribution, it is true, but not in the usual way, as there are geographical sub-species of 

 the common kind besides. We shall not attempt a solution here, but would like to 

 put the question thus : Why may not the birds with red crescent and red moustache 

 (this probably being the most numerous form of the so-called ' hybrid us'), be the 

 original stock, which, westward, became modified into mexicanus, eastward into 

 auratus, the isolated individuals, with mixed characters, being due to atavism, or occa- 

 sional outbreak of the characters of the original stock, Avhile a great many of the 

 mixed individuals from the intermediate region might be regarded as products of 

 hybridization? In other words, why not a trichromatism on the verge of forming- 

 three different species, or two if as would be expected the original (intermediate) 

 stock died out at last? A point which seems to strengthen such a view is the fact 



