1936] MAMMALS OP OREGON 233 



Breeding habits. The females have 4 pairs of mammae 1 ingui- 

 nal, 1 abdominal, and 2 pectoral. The number of young ranges from 

 4 to 8 in a litter; apparently but one litter is born in a season. 

 In some cases the young have scant time to get their growth and lay 

 in a stock of fat before winter. 



Food habits. These mice are dainty feeders, living mainly on 

 small seeds of grasses and other plants which they reach by cutting 

 off the stems, drawing them down and biting off the lower sections 

 until the seed-laden heads are reached. The small grains wheat, 

 barlev, rye, and oats are treated in the same manner and are also 

 favorite foods. Many other plants are also cut for their seeds, and 

 rolled oats used for trap bait are eagerly eaten. 



In the early autumn the animals accumulate an excessive amount 

 of fat in thick layers under the skin, over the muscles and especially 

 in the abdominal cavity. In the case of other subspecies this oily 

 fat will more than double their weight and supply ample food 

 material to carry them through the long winter's sleep. 



Economic status. Generally these little animals are not numerous 

 enough to be of any serious economic importance, but where they 

 are unusually numerous the meadows suffer in spots from the amount 

 of grass that they cut to get the seeds. In places an acre or more 

 of the best grasses may be found noticeably thinned by them. The 

 loss of seed locally may also prove a serious check on the reproduc- 

 tion of the grasses. Potentially they are thus capable of serious 

 injury to grain and forage crops, and every encouragement should 

 be given to their natural enemies, owls and other nocturnal birds, 

 weasels, skunks, badgers, and beasts of prey. 



ZAPUS TRINOTATUS PACIFICUS MERBIAM 

 PACIFIC JUMPING MOUSE 



Zapus pacific^ Men-lam, Biol. Soc. Wash. Proc. 11 : 104, 1897. 



Type. Collected at Prospect, Rogue River Valley, Oreg., by Edward A, Preble, 

 August 29, 1896. 



General characters. Small; form slender; skull narrow and slender; colors 

 bright, with much yellowish in dorsal area and unusually clear yellow sides, 

 lightly lined with black hairs; belly and lower surface of tail white; feet gray; 

 ears slightly or not at all edged with yellow. 



Measurements. Type, adult male: Total length, 225 mm; tail 141; foot, 31; 

 ear (dry), 12. 



Distribution^ and habitat. This mouse is found in the upper Rogue 

 River Valley in Oregon and extends southward into northern Cali- 

 fornia, in semiarid Transition Zone (fig. 52). 



General habits. No peculiarities of habits have been observed for 

 this form except the habit of swimming, which is probably common 

 to all. On the side of Preston Peak, Calif., X. Hollistef, in 1909, 

 gave the following interesting note : 



While I was walking around the grassy border of a small pond one jumped 

 ut at my feet and struck in the water like a frog, which at first it was thought 

 to be, until it was seen swimming across the pond on the surface of the water, 

 when it was shot for a specimen. The animal may not have intentionally 

 jumped into the water but he certainly handled himself as if perfectly at home 

 and swam with little effort and great speed over the still surface of the pond. 



