Vlll BIRDS OF THE COLORADO VALLEY 



liighly diverse topography of the country is strongly reflected 

 in the temiierature, the rainfall, and the course of the seasons 

 of this remarkable region, and these in turn leave their impress 

 upon animal and vegetable life, with the result that contiguous 

 areas of insignificant geographical extent may difi'er as much 

 in their natural productions as if they stretched over many 

 degrees of latitude. In the Colorado Basin, in fact, as appears 

 to be the case in most portions of Mexico, the distribution and 

 migrations of birds may be regarded as affected by altitude 

 rather than by latitude or longitude; and we have a striking 

 instance of the convertibility of these two factors of the general 

 equation. The birds here find their siunmer and winter homes, 

 and perform their migTations, rather according to "the lay of 

 the land" than Avith reference to degrees of latitude. 



A portion of the Colorado Valley, in Southwestern Arizona 

 and adjoining parts of California, has long been known as the 

 hottest place in the United States. At Fort Yuma, on the 

 Colorado Eiver at the mouth of the Gila, in latitude 32° 32', 

 longitude 114° 3G' 9", the mean annual rainfall does not exceed 

 five inches. A temperature of 119° F. has been recorded, and for 

 weeks in succession the merciuy may rise above 100° daily. For 

 several hundred miles the great river rises but little, its elevation 

 at Fort Mojave, for instance, being only about 525 feet. South- 

 ern and Western Arizona is a torrid, alkaline waste ; in fact, 

 a part of the "Great American Desert"; yet in the central 

 portion of the Territory rise the magnificent San Francisco 

 Mountains, 12,562 feet high, pine-clad, and snow-capped during 

 a portion of the year ; and at Fort Whipple, with an altitude 

 of 5,335 feet, the general course of the seasons is not materially 

 different from that in the Middle Atlantic States. A day's jour- 

 ney fi'om the last-mentioned locality will show differences in 

 the bird-fauna comparable, for instance, to those distinguish- 

 ing Massachusetts from the District of Columbia. Many of 

 the birds of Fort Yuma and Fort AVhipple respectively are total 

 strangers to each other. 



Such striking featiu'es as are here briefly indicated render the 

 study of the birds of this region specially attractive, and exact 

 information respecting their distribution and movements within 

 the area in question is very desirable. The whole subject is 

 elucidated in detaU in the present treatise. 



Aside from the local perturbations resulting from topograph- 

 ical and chniatic diversity within small areas, the bird-fauna 

 of the Colorado Valley is in a sense homogeneous and rather 



