64 University of California Publications in Zoology [Vol. 21 



indication of the time of origin or development of that character in 

 the species to which the individual belongs, then it would appear 

 that in Tconoma the bushj^ tail is a character which is fairly well 

 rooted. This is a character peculiar to, and present in, all individuals 

 of every known race in the subgenus Teonoma. It is the chief diag- 

 nostic character by which these animals may be recognized at a glance 

 among other wood rats, and it is in the author's estimation of more 

 than superficial importance. 



EELATION TO OTHEE ANIMALS 



The rockpiles in which bushy-tailed wood rats live are also inhab- 

 ited by other small mammals. The cony (Ochotona), golden-mantled 

 ground squirrel {Callospermophilus), alpine chipmunk {Eutaniias 

 alpinus), and the Sierra marmot (Marmota), have all been found 

 living as close neighbors with these wood rats in their rock-slide homes. 

 The following are some specific instances of this sort. At Vogelsang 

 Lake, in Yosemite National Park, six conies and one bushy-tailed wood 

 rat were trapped at one cony haypile. At Bullfrog Lake, Fresno 

 County, the first week of September, conies were regularly caught 

 in the daytime in rat traps set in the rock slides and baited with 

 rolled oats. These same traps caught an equal number of bushy-tailed 

 wood rats during the hours of darkness. The bushy-tails are thus 

 the nocturnal inhabitants of the rock-slide community. 



Certain advantages undoubtedl}' result from this commensal method 

 of living, one probable advantage being that it affords the small 

 herbivorous inhabitants a relatively greater degree of protection from 

 their carnivorous enemies than they would otherwise be able to secure. 

 The conies are on guard during the day while the wood rats are on 

 the alert during the night, so that it is difficult for any predator to 

 invade the community rock pile without some of the inhabitants detect- 

 ing his presence and spreading the alarm either by scurrying through 

 the passageways among the rocks or, as with the conies, by uttering 

 cries. 



The most important of these natural enemies are the Sierra pine 

 marten {Martes oaurina sierrae) and the mountain weasel {Mustela 

 arizonensis) . The mountain coj^ote (Canis latrans lestes) and the 

 horned owl {Buho virginianus) probably also levy some toll upon 

 the bushy-tailed wood rats which live at the lower altitudes, in the 

 pinon belt of the desert ranges or the shady caiions of the Sierra 



