DISTRIBUTION OF WARBLERS 



13 



sented in the east, i. e. Cardellina and Peucedramus of the Mexican 

 tableland, which cross our border in Arizona and New Mexico. The 

 east, on the contrary, has the 2 genera mentioned above as of probable 

 West Indian origin and also Mniotilta and Protonotaria. 



Chamwthlypis reaches our border on the Ibwer Rio Grande, and 

 Compsothlypis comes to us through the sarhe door and, evidently 

 finding the arid region of the west a bar to range extension in that 

 direction, has followed the humid coast to the north and east. Doubt- 

 less the origin of several other species (e. g. Oporornis formosus and 

 Wilsonia citrina) of eastern Warblers is to be accounted for in a 

 similar manner. 



The remaining 8 genera are common to both regions but it is 

 worthy of note that only i of them is presumably of West Indian origin. 

 Omitting, therefore, ChamcBthlypis and Compsothlypis, as occupying 

 neutral ground, the east has 12 genera of Warblers, the west 10. In 

 species, however, chiefly owing to the large number of species of Den- 

 droica derived from the West Indies, and to those of other genera 

 which have spread from eastern Mexico eastward, the difference 

 between the east and the west is more pronounced. It is expressed in 

 the following figures: Species found in both the east and west, 7; 

 species found only in the west, 13; species found only in the east, 32; 

 Texas species, 3 ; thus giving the east 39 species as against 20 for the 

 west. 



It should be added that this comparison is based on the Warblers 

 of the Atlantic States with those of the Pacific States, no account here 

 being taken of the northwestward distribution of some species to 

 Alaska bringing them properly into the bird-life of western North 

 America, though obviously of eastern origin. 



The subject is a wide one and absence of definite knowledge of 

 the past tempts us to speculate on the significance of the present. 

 This outline, however, may well be concluded by the appended 



Distributional Synopsis of the Family Mniotiltid^. 



Mniotilta, i species, eastern North America. 

 Helinaia, i species, eastern North America. 

 Helmitheros, i species, eastern North America. 

 Protonotaria, 1 species, eastern North America. 

 Vermivora, 9 species, 8 North America, 1 Mexico. 

 Oreothlypis, 2 species, Mexico and Central America. 

 Compsothlypis, 3 species, South America from Argentina north 

 to Central America, Mexico, and eastern North America. 



