4 Cooke, Routes of Bird Migration [j^ k 



of the Swallows, there is no evidence to show that any birds 

 migrate to the mouth of the Mississippi overland by way of 

 Florida or Texas. 



The Yellow Warbler (Dendroica cestiva) is one of the most com- 

 mon breeders throughout eastern North America, from the limit 

 of tree growth in the north to central Georgia. Then to the 

 southeast its numbers rapidly diminish, the species is practically 

 unknown in Florida in spring migration and the numbers that 

 occur in that State in the fall are but a tithe of those found to the 

 north and west. The Yellow Warbler is a common migrant in 

 eastern Mexico, especially in Yucatan and the islands off its east 

 coast, but no farther east. It is unknown in Cuba or any other 

 of the islands of the Greater Antilles and the avifauna of these 

 islands has been sufficiently studied so that it is certain that this 

 species can exist on them, if at all, only as a rare straggler. 



A line drawn from Savannah, Ga., to the islands off the east 

 coast of Yucatan marks approximately the eastern edge of the 

 district in which the Yellow Warbler is common, — to the west- 

 ward ubiquitous, to the eastward scarcely known. While no one 

 has tagged a Yellow Warbler in the Carolinas and captured that 

 same individual in Yucatan, it is a stretch of the imagination not 

 to believe that the Yellow Warblers of the eastern United States 

 pass in fall southwest, following the general trend of the Atlantic 

 Coast, and continue this same direction to Yucatan. It is certain 

 that they cross the Gulf of Mexico ; it is unlikely that they take 

 any unusual course when the shortest and most direct offers con- 

 genial conditions. 



The case of the Yellow Warbler has been given in full because 

 it is one of the commonest and best known species. The line of 

 reasoning is just the same for a number of other species that are 

 common in eastern United States and in Yucatan, but are rare or 

 unknown in southern Florida, Cuba, and the other West Indies. 



It is not meant, of course, that no individual of these species 

 ever passes through Florida to Cuba and on thence to Central or 

 South America. But what is meant is that the avifauna of Florida 

 and Cuba has been so thoroughly studied for so long a period that 

 the failure to find these species there except as stragglers is proof 

 positive that the large majority of the individuals choose some 

 other migration route. 



