204 NORTH AMERICAN FAUNA [No. 55 



nettle, pigweed, Atriplex, Dondia, and such vegetables and fruits as 

 cabbage, spinach, cantaloups, and apples. They do not care much 

 for potatoes but do eat them extensively when other food is scarce. 

 They are especially fond of all the clovers and alfalfa. 



Economic status. In captivity one of these mice which weighed 

 34.5 g reduced the weight of its bundle of green grass 27 g. almost 

 an ounce, in 24 hours, but this was not choice food, and related species 

 have been found to eat an average of their own weight in green 

 food every 24 hours. Allowing 1 ounce a day to a mouse and 10 mice 

 to an acre over the 40,000 acres of meadowland in the Malheur Valley, 

 they would eat about 4,400 tons of green grass, or approximately 

 2,200 tons of hay, in a year. Even 1 mouse to an acre, the lowest pos- 

 sible estimate at any season, would at this rate consume 220 tons of 

 hay in a year, an item of considerable importance in one valley. 



In Nevada in 1907 these mice devoured practically all the alfalfa 

 and most of the other crops, and killed many of the fruit and shade 

 trees in the lower Humboldt Valley, causing a loss to the ranchmen 

 estimated at $250,000. In this case their numbers in some of the 

 alfalfa fields were estimated at several thousand to an acre, far more 

 than a heavy crop of alfalfa could support for any considerable 

 length of time. Such conditions are possible anywhere under cir- 

 cumstances favorable to the rapid increase and complete protection 

 of the mice from their natural enemies. 



The remedy for much of the loss due to these mice i$ simple and 

 inexpensive: Clean fields and meadows, clean borders, ditch banks, 

 roadsides, and waste places so the hawks, owls, ravens, crows, mag- 

 pies, gulls, herons, foxes, skunks, badgers, and numerous other ene- 

 mies can see and capture these, their favorite prey. Only under 

 protecting cover can the mice become seriously harmful. 



MICROTUS NANUS NANUS 8 (MERMAM) 

 DWARF MEADOW MOUSE 



Arvicolu (Mynomes) nanus Merriam, North Amer. Fauna No. 5, p. 62, 1891. 



Type. Collected in Pahsimeroi Mountains, Idaho, at 9,300 feet altitude, 

 September 16, 1890, by Merriam and Bailey. 



General characters. Small; tail short; ears short and rounded; hip glands 

 conspicuous in old males; incisors slightly protruding, not curved abruptly 

 downward. Upper parts uniform sepia gray ; lower parts washed with white ; 

 tail distinctly tricolor, dusky gray above, whitish below ; feet gray. 



Measurements. Average of several typical adults: Total length, 143 nun; 

 tail, 37; foot, 19; ear (dry), 11. 



Distribution and habitat. These little gray meadow mice have a 

 wide range over the Rocky Mountain region from New Mexico to 

 Canada and reach their western limit in Oregon, occupying prac- 

 tically the whole Blue Mountain section and west to Hay Creek on 

 the ridge between the John Day and Deschutes Rivers (fig. 43). 

 A specimen from the high ridge north of Crane, on the southernmost 

 spur of the Blue Mountains, marks their southern limit in the State. 

 Generally they are found in Transition and Canadian Zones in open 



9 Some of the specimens along the lower edges of the Blue Mountain section are grading 

 toward the grayer subspecies, canescens, but none seen from the State is typical of that 

 form and all are here referred to nanus. 



