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THE NATIONAL GEOGRAPHIC MAGAZINE 



They feed upon a great variety of seeds, 

 fruits, roots, and succulent vegetable matter 

 and lay up stores for winter in underground 

 chambers or in hollow logs and similar places 

 above ground. 



With the coming of winter they gather about 

 cabins and other habitations in their territory 

 and become as persistent as house mice in 

 searching out and raiding food supplies of all 

 kinds. When the more appreciated kinds of 

 food fail they resort to gnawing the bark from 

 roots and bases of trunks of small deciduous 

 trees of various kinds. 



During my sledge journeys in the region 

 about Bering Strait I found the skins of many 

 red-backed mice among the Eskimo children. 

 The small boys kept them with lemming skins 

 as evidences of their prowess with miniature 

 dead-fall traps and blunt-pointed arrows, and 

 the little girls kept them as prized robes for the 

 dolls carved by their fathers from wood or wal- 

 rus ivory. 



THE RUFOUS TREE MOUSE (Phena- 

 comys longicaudus and its relatives) 



{For illustration, see page 523) 



The genus Phenacomys, to which the rufous 

 tree mouse belongs, includes a number of spe- 

 cies closely similar in size and external appear- 

 ance to some of the well-known field mice. 

 The structure of their teeth, however, shows 

 that they form a distinct group of animals. 



So far as known, the living members of the 

 genus are confined to the Boreal parts of North 

 America, where they range from the Atlantic 

 to the Pacific in Canada, and southward along 

 the mountains to New Hampshire, New Mex- 

 ico, and northern California. The discovery 

 of fossil representatives of the genus in Hun- 

 gary and England indicates that it was for- 

 merly circumpolar in distribution. 



All but one species of the genus live on the 

 ground, inhabit burrows, make runways through 

 the small vegetation, and feed on grasses and 

 other herbage— all in close conformity with the 

 habits of the meadow mice. 



The tree mouse, however, is a strongly aber- 

 rant member of the group. It differs from all 

 the others, and from all field mice, not only in 

 its rufous color and longer tail, but in its re- 

 markable mode of life. It is restricted to the 

 humid region of magnificent forests in western 

 Oregon and northwestern California, where it 

 often spends its life in the tops of such noble 

 trees as the Sitka spruce, the Douglas fir, and 

 the coast redwood. Such an amazing depar- 

 ture from the habits of its kind lends unusual 

 interest to this little animal. 



Its nests are generally located high up in the 

 trees, sometimes 100 feet from the ground,_ in 

 forests where the branches of neighboring 

 trees interlace so that it can pass from one to 

 another and inhabit a world of its own, free 

 from the ordinary four-footed enemies which 

 prowl below. 



The nests vary in size, structure, and loca- 

 tion. In Oregon they have been found only in 



large trees at elevations varying from 30 to 100 

 feet. On the seashore near Eureka, California, 

 they are placed on the branches of small sec- 

 ond-growth myrtle and redwood trees Far- 

 ther inland in the same region many are in 

 small trees, within a few yards of the ground, 

 on the border of heavy redwood forests. 



The higher nests of the tree mice are often 

 the deserted and remodeled homes of the big 

 gray tree squirrel of that region {Sciurus 

 griseus) and contain a foundation of coarser 

 sticks than in the nests wholly built by the 

 mice. The larger proportion of the nests are 

 built by the mice and are usually composed of 

 small twigs, fragments of a netlike lichen, skel- 

 etons of fir, spruce, or other coniferous leaves, 

 and the droppings of the mice themselves. 

 They vary from small oval structures a few 

 inches in diameter, located well out on the 

 branches, to great masses close against and 

 sometimes entirely surrounding the tree trunks, 

 supported on several branches, and measuring 

 three feet long and two or three feet high. 



The interior of these large structures is 

 pierced with numerous passageways and some- 

 times as many as five separate nest chambers 

 are scattered through one. Tunnels run out 

 along each of the limbs on which the mass 

 rests, and if it extends all the way round one 

 main tunnel encircles the trunk from which 

 these hallways branch. 



Such great nests have evidently been used 

 for a long period and have grown with the 

 steady accumulation of material. This has 

 gradually decayed and become a solid mass of 

 earthy humus. The large nests are usually the 

 abodes of a single female, the homes of the 

 males having been found to be small and more 

 often located away from the trunk of the tree. 

 The food of the red tree mouse, so far as 

 known, consists entirely of the fleshy parts of 

 fir and spruce needles and the bark from conif- 

 erous twigs. 



Tree mice appear to breed throughout most 

 of the year and have from one to four young 

 in a litter. They are mainly nocturnal, and 

 when driven from their nests by day appear 

 rather slow and uncertain in their movements. 

 Those living in highly placed nests usually es- 

 cape by running out on the limbs, and pass 

 from one tree to another if necessary. Those 

 in small trees usually drop quickly from limb 

 to limb until they reach the ground, when they 

 run to the nearest shelter. 



That these mice sometimes descend to the 

 ground of their own volition is prol^able. but 

 the fact that the stomach of every individual 

 so far examined has contained only the fleshy 

 parts of coniferous leaves indicate that their 

 food habits have become so fixed as to make 

 arboreal life a necessity. 



The modification of the habits of a member 

 of a group of ground - frequenting animals, 

 with a structure adapted to such an existence, 

 to those of a strictly arboreal animal is so 

 strange as to make the question of cause a 

 puzzling one. 



In the Hawaiian Islands the introduction of 

 the mongoose has made the common house rat 



