GEOGRAPHIC ISOLATION AND SPECIES-FORMING 121 



a subspecies, Dendroica ccstiva sonorana. Further south, in 

 central Mexico, this form runs larger in size and is recorded as 

 Dendroica (estiva dugesi. Northward, through to Alaska, we 

 have an ally of the parent bird, but smaller and still more 

 greenish. This is Dendroica cestiva rubiginosa. 



In the West Indies, the golden warblers migrate not from 

 north to south, but from the shore to the mountains, and, 

 possibly in consequence of the less demand of flight, the wing 

 is shorter and more rounded, while the tail is longer. As these 

 forms do not clearly intergrade with those of the mainland, 

 and, for the most part, not with each other, they are held to 

 represent a number of distinct species, although doubtless 

 derived from the parent stock of Dendroica cestiva. Some of 

 these West Indian forms are relatively large, the wing more 

 than five inches long, and the longest known of these, the type 

 of the species for this reason, found in Jamaica, is called Dendro- 

 ica petechia. On the island of Grand Cayman is a similar 

 bird, a little smaller, Dendroica auricapilla. Of a deeper 

 yellow than petechia, and equally large, is the golden warbler 

 of the Lesser Antilles ranging from island to island, from Porto 

 Rico to Antigua. This form, first known from St. Bartholomew, 

 is Dendroica petechia bartholemica. A smaller bird, a little 

 different in color, takes its place in the Bahamas. This is 

 Dendroica petechia flaviceps. 



In Cuba, the golden warbler is darker and more olive, with 

 other minor differences from the form called bartholemica, of 

 which it may be the parent. This is Dendroica petechia gund- 

 lachi. A similar bird, but with the crown distinctly chestnut, 

 is Dendroica petechia aureola, the golden warbler of the Gala- 

 pagos and Cocos Islands, off the coast of Ecuador and Peru. 

 Scattered over other islands are smaller golden warblers with 

 the wing less than five inches long, and with the crown tawny 

 red, as in aureola. These are known collectively as Dendroica 

 ruficapilla, the type being from Guadeloupe and Dominica. 

 More heavily streaked, with the crown darker in color, is the 

 golden warbler of Cozumel, Dendroica ruficapilla flavivertex, 

 and with very similar but with darker crown is Dendroica 

 ruficapilla flavida, of the island of St. Andrews. Always, the 

 nearest form lies across the barrier, and among these island 

 forms the chief barrier is the sea. With a darker chestnut 

 crown is Dendroica ruficapilla rufopileata, of the island of 



