PORCUPINE 153 



young and inexperienced individuals of those species, do venture to attack 

 porcupines. Often the attacker receives a load of quills for his pains. We 

 have seen a coyote with jaws and feet literally filled with the barbed quills 

 of a porcupine. Occasionally wildcats are found with porcupine quills 

 imbedded in their flesh, particularly about the head and forelegs. Local 

 information is rather scant as to the exact measure of success attained by 

 those species which prey or attempt to prey upon the porcupine. 



The Yellow-haired Porcupine is a bark feeder, that is, it subsists on 

 the soft growing tissues (cambium) found at the junction of the inner 

 bark and outermost wood in a growing tree. Its preferred food tree in 

 the Yosemite region is the lodgepole pine, probably because least effort is 

 required to obtain the cambium in that thin-barked tree. This sort of 

 food is available at all seasons of the year and the porcupine therefore 

 has no need to lay up a food supply nor to hibernate, or migrate, as do 

 many of the other herbivorous mammals. The abundance of easily obtained 

 food probably accounts in large measure for the porcupine's sedentary 

 nature. At several points in the Yosemite region we saw trees whose con- 

 dition indicated that a porcupine had wintered in a very restricted area, 

 and had probably spent many days in each one of the few trees which had 

 been peeled. To get at its food the porcupine shells or scales off the outer 

 bark and then actively gnaws off the tender growing tissue. 



A most favorable locality in which to study the work of this animal is 

 the place on the Tioga Road called Porcupine Flat. The territory com- 

 prising Porcupine Flat was once occupied by one or more glaciers, and 

 the terminal moraine of one small glacier forms a lake there. This glacia- 

 tion cleared the surface down to bedrock. Since the glaciers have dis- 

 appeared only a small amount of soil has accumulated on the surface of 

 the rock. All the trees are therefore shallow rooted and may be easily 

 struck down by storms. The trees newly prostrated provide easily accessible 

 food for the porcupines. 



Porcupine Flat is well named, to judge from the amount of the porcu- 

 pine work which we saw there. The forest on parts of the nearly level floor 

 is purely of lodgepole pine ranging from well spaced trees as much as 

 3 feet in diameter down to small saplings in dense groves of an acre or 

 so in extent. There was, in June, 1915, much fallen timber, including 

 scores of trees which had been downed the preceding winter or possibly 

 within three months, for much of the foliage was still green. These trees 

 showed that the porcupines had been very busy ; they bore marks of incisor 

 teeth on trunks, on large branches, and even on twigs down to half an inch 

 in diameter. (See pi. 37a.) These gnawed places were all 'bleeding' much 

 pitch at the time of our visit. Evidently, for j^ears, the porcupines had 

 regularly taken advantage of these local circumstances, and so avoided the 



