132 ANIMAL LIFE IN DESERTS 



only the two woodpeckers are equipped for making 

 these excavations. So that, without the wood- 

 peckers to make holes, the other birds would be 

 no better off for the presence of saguaro." The 

 two woodpeckers to which he refers are the Gila 

 Woodpecker (Genturus uropygialis) and Mearn's 

 Gilded Fhcker {Colaptes chrysoides mearnsi). The 

 range of these woodpeckers is wider than that of 

 the Giant Cactus, and they have been found breeding 

 in trees of various species along the banks of the 

 California River. But wherever the Giant Cactus 

 grows the two woodpeckers are found, and found 

 more commonly than in other places, and when 

 it is possible the woodpeckers hew their nesting- 

 hole in this plant and nothing else. But for its 

 existence the birds would be confined to the river- 

 side growth of Cottonwood and willow; but as 

 they can excavate nesting-sites in the cactus they 

 are able to colonize desert areas where no other 

 large vegetation grows. Other parts of the same 

 deserts where there is no Giant Cactus have a 

 much poorer avifauna, for neither the woodpeckers 

 nor the birds which are dependent upon them are 

 foxmd there. The association between the Giant 

 Cactus and the two woodpeckers is closer because 

 the woodpeckers are strictly resident birds, remain- 

 ing all the year where they breed, and not wandering 

 far from that place at any season. As Grinnell 

 impUes in the passage which I have quoted, other 

 birds use the woodpeckers' nesting-holes, after the 

 woodpeckers have vacated them. The Elf Owl 

 (Micropallas whitneyi) is found exclusively in deserts 



