52 University of California Publications in Zoology [Vol.12 



marks the southeastern boundary of California, comprising the interval 

 between the Nevada line and the Mexican line, and separates our state 

 from Arizona. Biogeographically, the Colorado River completely 

 bisects the desert area through which it flows, the resultant two di- 

 visions with their xerophilous fauna and flora being separated, not 

 only by the stream itself, but also by the riparian strips of more of 

 less width which flank the river immediately on either side. 



Two objects were in mind to justify the selection of the Colorado 

 valley for extended field-work in vertebrate zoology : ( 1 ) The literature 

 pertaining to the birds and mammals of the region was fragmentary. 

 relatively little work having been published since the early and incom- 

 plete reports of Woodhouse (1853), Cooper (1861, 1868, 1869), and 

 Coues (1866). An extended knowledge of the composition of the 

 vertebrate fauna of the southeastern frontier of California was a 

 desideratum. (2) The effect of the Colorado River, with its riparian 

 strips sharply contrasted against the contiguous desert areas, upon the 

 distribution of the animals concerned, promised to provide data of 

 importance relative to the general problem of barriers. 



Miss Annie M. Alexander, founder of the California Museum of 

 Vertebrate Zoology, not only warmly approved of the plan to under- 

 take field-work along the lower Colorado River with the above objects 

 in view, but generously provided the necessary cost of the expedition 

 in addition to her regular appropriation for the support of the museum. 

 The plan was carried out in the three months of 1910 from February 

 15 to May 15, inclusive. The writer took part in the field work- 

 in person throughout the entire time, and was assisted by Mr. Frank 

 Stephens, Mr. Joseph Dixon, and Mr. L. Hollister Jones. The party 

 began work at Needles, and proceeded by boat from place to place 

 down the river, the last station being on the California side below 

 Yuma and close to the Mexican line. The locations of the various 

 collecting stations established are given in the itinerary. 



The three months' field-work yielded 1,272 specimens of mammals, 

 1,374 birds. 443 reptiles and amphibians, 22 sets of birds' eggs and 

 nests, a few fishes, and a collection of the more conspicuous plants. 

 All of this material now forms part of the collections of the Cali- 

 fornia Museum of Vertebrate Zoology, except the plants, which are 

 deposited in the Herbarium of the Department of Botany of the 

 University of California, and the few fishes, which are added to the 

 ichthyologieal collection in the Zoological Department of Leland Stan- 

 ford Junior University. 



