EVOLUTION OF THE COLORS OF BIRDS. 237 



Icteria and Sylvania (Myiodioctes) make the northern 

 woods and swamps gay with their parti-colored attire, 

 while Dendroica, which should have been included in 

 the list, is still more varied and resplendent in its dress; 

 to say nothing of the Trochilidae or the beautiful part- 

 ridges of the west Oreortyx, Callipepla, and the rest. 

 The Trochilidse may be excluded from this list as un- 

 questionably of Neotropical origin, leaving only two or 

 three of the warblers in the list of really brilliant colored 

 species representative of the Nearctic region. Further- 

 more, it is noticeable that with the exception of the 

 blackbirds and humming-birds, irridescent or metallic 

 colors are almost wanting. 



It thus becomes apparent that there is some general 

 connection between the geographical distribution and 

 color of birds. The species found in the arctics are, for 

 the most part, white in color, those which take their 

 origin in the north temperate zone are to a large extent 

 plainly colored, while the brilliant species have appar- 

 ently nearly always originated in the tropics, In the 

 above lists of Nearctic genera another fact is noticeable, 

 viz.: The large number of birds marked with streaks. 

 Such, for example, are Harporhynchus, Certhia, Mnio- 

 tilta, Passerella, Leucosticte, Melospiza, Ammodramus, 

 Pooecetes, etc. Reasons have been given for consider- 

 ing this style of coloration more primitive than any 

 other. Assuming this to be true, it is a curious circum- 

 stance that the oldest stock of birds should be the least 

 specialized in their colors. This does not seem so sur- 

 prising, however, when we consider the disadvantages 

 under which they have lived as compared with their 

 southern allies. One of the greatest has been an in- 

 auspicious climate. The cold of the glacial period in 

 particular must have made food very scarce and compe- 

 tition very keen, so that all the energy of the bird was 



