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THE NATIONAL GEOGRAPHIC MAGAZINE 



of these mice extends from sea level to an 

 altitude of more than 7,000 feet. 



As with the majority of our wild mammals, 

 little accurate information is available concern- 

 ing their life history. They are habitants 

 mainly of desert regions, where they prefer the 

 areas of sandy loam, which produce an abun- 

 dance of scattered desert vegetation. They are 

 nocturnal and by day are seen only when 

 driven from their nests. Their rather shallow 

 burrows are made in soft soil, the situation 

 varying a little with the species. Some species 

 burrow only under the shelter of bushes or 

 other vegetation ; others out in the bare ground. 



Each burrow commonly has grouped in a 

 small area several entrance holes, which lead 

 through tunnels to the central passageway, the 

 nest, and the storage chambers. Usually there 

 is a little pile of loose dirt thrown out on one 

 side of a hole, or a group of holes may be in a 

 little mound of earth. The entrances are usu- 

 ally stopped from within by loose earth, and if 

 a person quietly thrusts in a short stick so as. 

 to remove the earthy plug and let in the light 

 he may see the dirt suddenly returned to its 

 place in little jets, as the occupant promptly 

 kicks the door closed again. 



The young, varying from two to six in a 

 litter, are born in these little dens in warm 

 nests of dried grasses. They have been found 

 at all times between April and September, thus 

 making it apparent that several litters are pro- 

 duced each season. 



The silky, as well as the other kinds of des- 

 ert pocket mice, do not drink water, and, as 

 has been shown by experiments, they may be 

 kept for months in thoroughly dry sand and 

 fed on dried seeds without any resulting dis- 

 comfort. Through the long pressure of desert 

 environment they have developed the power to 

 produce sufficient water for their physiological 

 processes by chemical changes in the starch in 

 their food, which are effected in the digestive 

 tract. 



Representatives of this group of mice are al- 

 most everywhere in the arid parts of their 

 range, and in many sandy localities are ex- 

 tremely numerous and active at night, as shown 

 by the multitude of little tracks in the dust at 

 sunrise each morning. Their presence in the 

 desert is indicated also by the many little coni- 

 cal pits half an inch or an inch deep, where 

 they have located small seeds and dug them up. 



They lie close in their burrows during cold 

 or stormy weather, depending on their stores 

 for food, but are not known to hibernate, al- 

 though in the northern part of their range they 

 are confined to their burrows for long periods. 



At one of my camps in the desert of Lower 

 California I found the silky and other pocket 

 mice excessively numerous and so short of 

 food that they swarmed about us at night with 

 amazing lack of fear. My experiences with 

 them are given in the accompanying account of 

 the spiny pocket mice. 



The silky and other pocket mice have many 

 enemies, among the worst of which are the 

 handsome little desert fox and the coyote. 

 Others which continually prey upon them are 



the badger, skunk, and bobcat, as well as many 



owls. 



THE SPINY POCKET MICE (Perog- 

 nathus hispidus and its relatives) 



(For illustration, sec pa</c lis) 



Pocket mice are divided into several natural 

 groups of species, all having certain characters 

 in common, as a pointed head, lengthened hind 

 feet and legs, and external cheek pouches for 



carrying food. The spiny group contains nu- 

 merous species, the smallest of which is about 

 the size of a house mouse and the largest 

 nearly twice that size. 



They are more slenderly built than the silky 

 species and have longer tails, with the hairs 

 lengthened along the terminal half, thus giving 

 a slightly brushy or tufted appearance. Their 

 most striking character is the distinctly coarser 

 hair with long scattered guard hairs, like small 

 bristles, which conspicuously overlie the fur on 

 the hinder parts of the body and from which 

 the common name is derived. 



The distribution of the spiny forms, although 

 nearly the same as that of the silky ones, is a 

 little more restricted. All belong to the arid 

 or desert parts of the West and Southwest, 

 from South Dakota and middle California 

 southward to Michoacan, near the southern 

 end of the Mexican tableland, and throughout 

 Lower California. 



Some species inhabit the scattered growth of 

 plants in sandy areas, but they are more gener- 

 ally characteristic of harder and more roek- 

 strewn soil, rocky mesas, and foothill slopes. 

 There a few species make burrows in open 

 ground, sometimes with a single hole, but most 

 of them make their nests under rocks, in crev- 

 ices, or in burrows sheltered by such desert 

 bushes as Covillea, Bursera, Olneya, Cercidium, 

 and mesquites. 



In these shelters pocket mice make little 

 mounds a few inches high and ten or fifteen 

 inches across. The mounds have several en- 

 trances on different sides, one of which gen- 

 erally shows signs of recent use, although by 

 day it is kept closed from within by loose earth. 

 Each of the many-entranced dens is occupied 

 by a single animal. Early in the morning, be- 

 fore the wind fills them with dust, tiny trails 

 are to be seen leading from these doorways 

 toward the nearest feeding grounds and all 

 about their haunts. 



The spiny and the silky pocket mice, sharing 

 much the same arid region, have the same food 

 plants and are preyed upon by the same ene- 

 mies. The food of these mice consists mainly 

 of small seeds, including the wild morning 

 glory, wild sunflowers, wild parsnips, and a 

 multitude of others characteristic of the vari- 

 ous areas they occupy. 



Pocket mice are strictly nocturnal or crepus- 

 cular in habits and appear by day only when 

 disturbed. If the plugged entrance to a bur- 

 row is opened, however, it will probably be 

 quickly stopped up again from within by the 

 annoyed householder. 



