80 



rniversiiy of California Publications in Zoologij [Vol. 12 



the open gTound 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 saltbnsh association and of the willow association are (luite the 

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

 the former graminivorous or spermopliilous. 



Creosote Assoclvtion (Mesa) 

 BIRDS 



(liordeiles acutipennis texeusis: 



max.; summer 

 Sayornis sayus sayus: min.; winter 

 Spizella breweri: min.; winter 

 Amphispiza bilineata lieserticola: 



max.; summer 



Amphispiza nevadensis nevadensis: 



min.; winter 

 Piranga ludoviciana: min.; transient 

 Salpinetes obsoletus obsoletus: min.; 



winter 



Ammospermophilus harrisi harrisi: 



min. (stony) 

 Ammospermophilus leucurus leucurus: 



min. (stony) 

 Citellus tereticaudus tereticaudus: 



min. (sandy) 

 Feromvscus eremicus eremicus: min. 



(sandy) 

 Thomomys chrysonotus: excl. 

 Dipodomys deserti deserti: min. 



(sandy) 

 Dipodomys merriami merriami: max. 

 Perognathus bombycinus: excl. 



(sandy) 

 Perognathus forniosus: min. (stony) 



Perognathus penicillatus penicillatus: 



min. (sandy) 

 Perognathus intermedins: min. 



(stony) 

 Perognathus spinatus spinatus: min. 



(stony) 

 Lepus calif ornicus deserticola: max. 

 Canis oehropus estor: max. (foraged 



at night practically everywhere 



else) 

 Vulpes macrotis arsipus: excl. 

 Myotis velifer: max. (?) 

 Eptesieus fuscus: max. (?) 

 Macrotus calif ornicus: max. (?) 



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

 (Larrea 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 otlier ligneous vegetation. These areas, where 



