Part 10

NATURAL HISTORY

Habitat.--On the Olympic Peninsula, Washington, in 1931 Svihla and Svihla (1933:132) found this species equally abundant in alpine meadows near timberline, in open grassy areas, and in tall meadow grass and low blueberry bushes. All of the mice were in wet marshy places. Bailey (1936:232) reported that in Oregon, these mice live in meadows, marshes, under ferns and weeds in the woods, or near mountain brooks and streams. Taylor (1922:221) found Zapus in moderately moist meadows in the Hudsonian Life-zone at Mt. Rainier, Washington, and Dice (1932:49) found them in deciduous forest and in open, grassy, or sphagnum bogs. Dice records it as common also among the alders and willows in high, open, grassy parks. Merriam (1897b:223) found Z. trinotatus abundantly in moist places grown-over with grass or weeds. Grass cuttings two to three inches long were left in small heaps at feeding sites and indicate the presence of these mice.

Behavior.--Svihla and Svihla (1933:131) write that the long tail of Z. trinotatus is used as a balancing organ when the mouse is in motion. A tailless mouse, attempting to escape, turned somersaults in the air and invariably landed on its back; the loss of its tail seemed to leave the mouse without compensation for the vigorous push of the hind legs. Dalquest (1948:371) noted that the jumping mouse sometimes walks on all fours, but ordinarily moves by means of short hops on the hind feet alone. When startled, jumping mice travel in bounds of six feet or more at a jump.

Zapus trinotatus, according to Bailey (1936:232) and Elliot (1899:261), is mainly nocturnal but occasionally is active in daylight.

Svihla and Svihla (op. cit.:132) heard captive animals make squeaking noises when fighting. On several occasions captive animals made a drumming noise by rapidly beating the tail against a resonant body such as the bottom of a tin can.

Concerning hibernation, Bailey (loc. cit.) remarks that animals of this species in Oregon, become fat in early autumn and lay down excess adipose tissue under the skin, over the muscles, and in the abdominal cavity. Svihla and Svihla (op. cit.:133) noted that captives from the Olympic Peninsula, Washington, gained weight in September and October and became extremely fat. With the additional weight they were more listless and drowsy, often spending days curled up in the hibernating position with the head between the hind legs and the long tail curled completely over the head and body. Warmth aroused the animals to activity, but when the temperature dropped they again hibernated. Flahaut (1939:17) reported the discovery on February 23, 1939, at Henderson Inlet, South Bay, Thurston County, Washington, of two nest cavities inhabited by jumping mice that were hibernating. The nests, four inches apart and 30 inches below the surface of the ground, were approximately five inches in diameter and made of shredded paper. Both mice were dormant, covered by nesting materials and curled up in the aforementioned hibernating posture. Dalquest (1948: 371) writes that in the lowlands of Washington this species disappears by late July but that in the mountains it remains active until the middle of September. Edson (1932:56) records an individual taken on April 20 from its place of hibernation beneath the roots of a decaying stump. This animal quickly roused in the warm mid-afternoon sun but became dormant again when the temperature dropped to 45° F. It seems that animals near the end of hibernation become active on warm days and return to the torpid state on cold ones.

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

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.

Description.--Size medium; color dull; back near Ochraceous-Buff with heavy admixture of black hairs, forming broad dorsal band; sides from near Ochraceous-Buff to near Ochraceous-Salmon, sometimes with heavy admixture of black hairs; lateral line usually distinct, sometimes blending with color of belly and side; ventral surface usually suffused with color of sides; tail bicolored, dark brown above, white to yellowish-white below; feet grayish-white above; ears dark, edged with color of sides; auditory bullae large; pterygoid fossae broad; incisive foramina relatively short; palatal bridge short; maxillary tooth-rows relatively short; narrow across zygomata; braincase narrow; interorbital region narrow; zygomatic arch relatively short.

Comparisons.--From Zapus trinotatus trinotatus, Z. t. eureka differs in: Size smaller; ventral surface with much greater suffusion of ochraceous; auditory bullae larger; pterygoid fossae relatively broader; frontal region less inflated; palatal bridge shorter; braincase narrower; narrow across zygomata; upper tooth-rows shorter.

For comparison with Zapus trinotatus orarius see account of that subspecies.

Remarks.--Howell (1920:230), without having examined the material, provisionally referred specimens from Requa and Crescent City, Del Norte County, California, to Z. t. eureka. I have studied this material and find the specimens to be intermediate between Z. t. trinotatus and Z. t. eureka in cranial characters (zygomatic breadth, interorbital width, and breadth of braincase), but nearer Z. t. trinotatus in coloration (absence of ochraceous suffusion ventrally). They are here referred to Z. t. trinotatus. The zone of intergradation between Z. t. trinotatus and Z. t. eureka seems to extend from Requa, California, north to Gold Beach, Oregon, where other specimens intermediate between these two subspecies, have been obtained. These individuals are also referred to Z. t. trinotatus on the basis of cranial features and color.

Specimens examined.--Total, 42, all from California, distributed as follows: Humboldt Co.: Trinidad, 4 (SDM); Carsons Camp, Mad River, 3 (USBS); 3 mi. W Arcata, 5 (MVZ); 7-3/10 mi. E Bayside, 1 (MVZ); 12 mi. S Korbel, on Maple Creek, 2 (MVZ); Falk, 1 (MVZ); Carlotta, 1 (MVZ); F. B. Summer Redwoods, S Eureka, 1 (MVZ); Maple Creek, 1 mi. W junction Mad River, 12 (MVZ). Mendocino County: Mendocino City, 1 (MVZ); Albion River, 1/3 mi. E MacDonalds Ranch, 1 (MVZ); Russian Gulch State Park, 10 (MVZ).

Marginal records.--California: Trinidad; Russian Gulch State Park; Albion River, 1/3 mi. E MacDonalds Ranch; Mendocino City; Carlotta.

=Zapus trinotatus montanus= Merriam

Zapus trinotatus montanus Merriam, Proc. Biol. Soc. Washington, 11:104, April 26, 1897; Bailey, N. Amer. Fauna, 55:234, August 29, 1936.

Zapus montanus, Preble, N. Amer. Fauna, 15:28, August 8, 1899.

Type.--Female, adult, skin and skull; No. 79863, U. S. Nat. Mus., Biol. Surv. Coll.; Crater Lake, Klamath County, Oregon; obtained on August 19, 1896, by Edward A. Preble, original No. 1388.

Range.--From Crater Lake, Klamath County, Oregon, northward along the Cascade Range into Hood River County, Oregon. Zonal range: Transition and Canadian.

Description.--Size medium; back near Ochraceous-Buff with admixture of black hair, resulting in a grizzled, broad, dorsal band; sides lighter than back, from near Ochraceous-Buff to near Pinkish-Cinnamon, and lined with black hair; lateral line distinct; underparts usually pure white, sometimes with slight suffusion of ochraceous on lower throat and upper chest; tail bicolored, brown above and yellowish-white below; ears dark, sometimes flecked with ochraceous, edged with yellowish-white; feet grayish-white above; braincase relatively narrow; zygomata relatively short; condylobasal length short; mastoid region relatively narrow; palatal bridge short; auditory bullae large; frontal region inflated; pterygoid fossae relatively narrow.