80 University of California Publications in Zoology [Vol.12 



the open ground between the shrubs. One such plant, gathered exten- 

 sively by Dipodomys deserti, is Achyronychia cooperi. 



It will be noted that the food-relations of the birds and mammals 

 of the saltbush association and of the willow association are quite the 

 reverse of one another; in the latter, insectivorous species prevail, in 

 the former graminivorous or spermophilous. 



Creosote Association (Mesa) 

 BIRDS 



(hordeiles acutipennis texensis: Amphispiza nevadensis nevadensis: 



max.; summer min.; winter 



Sayornis sayus sayus: min.; winter Piranga ludoviciana: min.; transient 



Spizella breweri: min.; winter Salpinctes obsoletus obsoletus: min.; 

 Amphispiza bilineata desertieola: winter 



max.; summer 



Ammospermopbilus harrisi harrisi: Perognathus penicillatus penicillatus: 



min. (stony) min. (sandy) 



Ammospermophilus leucurus leucurus: - Perognathus intermedins: min. 



min. (stony) (stony) 



t'itellus tereticaudus tereticaudus: Perognathus spinatus spinatus: min. 



min. (sandy) (stony) 



Peromyscus eremicus eremicus: min. Lepus calif ornicus desertieola: max. 



(sandy) Canis oehropus estor: max. (foraged 

 Thnmomys ehrysonotus: excl. at night practically everywhere 



Dipodomys deserti deserti: min. else) 



(sandy) Vulpes macrotis arsipus: excl. 



Dipodomys merriami merriami: max. Myotis velifer: max. (?) 



Perognathus bombyeinus: excl. Eptesieus fuscus: max. (?) 



(sandy) Macrotus californicus: max. (?) 

 Perognathus formosus: min. (stony) 



Remarks upon the Creosote Association (Mesa). — The creosote bush 

 if. am a divaricata) was found to be the most widely distributed 

 shrubby species of all the desert plants (see pi. 10, fig. 14). It 

 occurred in varying abundance from the second bottom and wash- 

 sides to the tops of the highest hills. Only the most rocky hill slopes, 

 and the periodically eroded wash-bottoms, lacked this plant altogether. 

 Yet there were obviously preferred areas of growth, or, still more 

 notable in this connection, areas where the creosote bush grew to the 

 entire exclusion of all other ligneous vegetation. These areas, where 



