Migrations of North American Birds. 277 



is probably the route by which most species of the Eastern 

 province reach INIiddle America^ rather than along the coast of 

 Texas and Mexico, many species being recorded in Guatemala 

 and Honduras, not noted in Mexico north of Yucatan. It is 

 the species of the Middle province that characterize more es- 

 pecially the winter fauna of Central Mexico, particularly its 

 western slope and Cape St. Lucas ; and it is an interesting fact 

 that very few of the birds peculiar to the Western province are 

 known to occur in Mexico at all. The North American winter 

 birds of Western Mexico, as stated, belong almost entirely to 

 the Middle fauna, the most notable exceptions being the oc- 

 currence at Colima and Manzanillo of Dendrceca superciliosa, 

 Sterna antillarum, and Chroicocephalus atricilla, and at Mazatlan 

 of D. superciliosa, Mniotilta varia, and Siurus aurocapillus, none 

 of them being found in California. The birds of Eastern 

 Mexico are likewise in large proportion from the Eastern 

 province of North America. 



It may perhaps be proper to recall attention to the fact that, 

 in defining the southern boundary of the Middle province and 

 at the same time that of North America as a zoological region, 

 I drew the line from the mouth of the Rio Grande of Texas to 

 that of the Yaqui River at Guaymas on the Gulf of California. 

 The space embraced between this line and the continental 

 portion of South America, including Mexico, Central America, 

 the Isthmus of Panama and of Darien, and the entire West 

 Indies, I term Middle America; all south of this. South 

 America. Trinidad alone, of the West Indies, belongs rather 

 to South America, most of its species being common to the 

 adjacent mainland, though some are, perhaps, peculiar to it. 

 Tobago, further north, though with some South American spe- 

 cies, has yet a considerable number peculiar to itself. 



In concluding this part of my remarks, I may state that the 

 present lists and generalizations in regard to the distribution 

 of our birds are to be considered merely provisional, and that 

 investigations at present in progress by myself and others will, 

 it is hoped, impart much greater precision to the knowledge of 

 the subject. In many instances I have omitted species which 

 might have been considered entitled to a place in one or the 



