_Enemies._--Little is recorded concerning enemies of _Z. trinotatus_, but Bailey (1936:233) lists owls and other nocturnal birds, weasels, skunks, and badgers as preying on this mouse. Smith and Hopkins (1937:191) found _Z. t. orarius_ in barn owl pellets obtained in Elk Valley, Marin County, California.
_Food._--Bailey (_loc. cit._) remarks that in Oregon, these mice feed mainly on small seeds of grasses, small grains (wheat, barley, oats, and rye), and other plants. These seeds are obtained by cutting the stems, drawing the stems down and biting off lower sections until the seed-laden heads are reached. Bailey (_op. cit._:234) found that _trinotatus_ utilized also the seeds of the western skunk cabbage.
Near Seattle, Washington, according to Dalquest (_loc. cit._), the principal food of _Z. trinotatus_ was velvet grass (_Holchus lanatus_), broad-leaved dock, and the seeds of other grasses. Dalquest reports also that the fruit of the blackberry (_Rubus macropelatus_) is eaten and that an occasional jumping mouse has its chin stained a deep purple by juice from these berries.
_Reproduction._--There is normally a single litter of from four to eight young per year according to Bailey (_loc. cit._). Newly born young have been described by Svihla and Svihla (1933:132) as follows: slightly smaller than newly born harvest mice (_Reithrodontomys m. megalotis_), average weight .8 grams, hairless (without even vibrissae visible), pink, eyes closed, ears folded, heads short and stubby, tails long (longer than those of newly born _Peromyscus_), and bodies surprisingly small (when compared with newly born _Peromyscus maniculatus_).
_Zapus trinotatus eureka_ A. B. Howell, Univ. California Publ., Zool. 21:229, May 20, 1920.
_Zapus trinotatus trinotatus_, Preble, N. Amer. Fauna, 15:26, August 8, 1899 (part--the part from Crescent City and Carsons Camp, Mad River, California).
_Zapus orarius_ Preble, N. Amer. Fauna, 15:29, August 8, 1899 (part--the part from Eureka and Carsons Camp, Mad River, California).
_Type._--Female, adult, skin and skull, No. 11703, Mus. Vert. Zool.; Fair Oaks, Humboldt County, California; obtained on August 27, 1910, by Joseph S. Dixon, original No. 1743.
_Range._--Northwestern coastal region of California, from Russian Gulch State Park, Mendocino County north to Trinidad, Humboldt County. Zonal range: humid Transition.