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THE NATIONAL GEOGRAPHIC MAGAZINE 



available. This completed, they set busily at 

 work nights to raid the food supply of the 

 owner and hide it in suitable storage places, 

 such as a crevice among boxes, an old shoe or 

 a pocket in a garment hung on the wall. Their 

 depredations usually cause so much exaspera- 

 tion that the camper overlooks the grace and 

 beauty of his visitors and makes every effort 

 to destroy them. If the occupants of such 

 camps would keep their supplies in mouse-proof 

 containers and would then feed their wood- 

 land friends, they would find them quickly re- 

 sponsive and most attractive guests. 



In their native haunts these mice have habits 

 varying with varying conditions. On brushy 

 plains they burrow in the ground, while in the 

 woods they sometimes burrow under rocks, 

 stumps, and logs, or live in hollows in stumps 

 and trees. As nimble in climbing as squirrels, 

 many live in hollow trees sometimes more than 

 fifty feet above the ground. 



That our inability to see at night prevents 

 more than an occasional glimpse at the doings 

 of the small animals which often swarm all 

 about us was impressed on me at one of my 

 camps in the desert of Lower California. My 

 blankets were spread under a small leafless tree 

 growing near the base of a rocky ledge, in the 

 crevices of which many relatives of the white- 

 footed mice were living. The first morning in 

 camp I awoke as the sky began to pale and 

 color with the approach of day. The dry 

 branches of the tree a few feet overhead be- 

 came sharply silhouetted against the sky, reveal- 

 ing several of the mice running up and down 

 them and leaping from twig to twig with all 

 the active grace of tiny squirrels. 



The mice appeared to be racing about in pure 

 playful enjoyment of the exercise, and when 

 the light had increased sufficiently to render 

 objects on the ground distinct they suddenly 

 ran down the tree trunk and vanished in a 

 crevice in the rocks. This game was repeated 

 on several succeeding mornings and is no doubt 

 commonly indulged in where conditions are 

 favorable. 



White-footed mice feed mainly on many 

 kinds of seeds and nuts and vary this diet with 

 snails, insects, and sometimes with the flesh of 

 dead birds or other mice. As they do not hi- 

 bernate they lay up abundant stores of grain 

 and seeds of many kinds in addition to a vari- 

 ety of nuts, as acorns, beech nuts, pine nuts, 

 maple seeds, and others, according to the local- 

 ity. The stores are hidden in hollows in logs, 

 stumps, trees, or in the ground. When in cap- 

 tivity they have shown themselves expert in 

 catching flies, sometimes capturing them with 

 their teeth and again with their front paws used 

 with all the dexterity of little hands. 



Several litters of young containing from 

 three to seven each are born, the first usually 

 appearing in spring and the last in fall. The 

 young are blind and helpless at birth, and in 

 this condition cling so tenaciously to the moth- 

 er's teats that when she is frightened from the 

 nest they are often carried off attached to her. 



Some individuals at least of the white-footed 

 mice, like others of the genus Peromyscus, are 



known to have a prolonged and musical song. 

 It is a line warbling ditty, a little like the song 

 of a canary. A number of good observers 

 have recorded these performances, but the>' 

 appear to be so infrequent that most peopli 

 with woodland experience have never heard 

 them. 



The lives of these mice are passed in con- 

 stant fear of a host of enemies. Hawks and 

 owls, bluejays, and shrikes in the bird world 

 are ever on the alert to capture them, while 

 skunks, weasels, minks, foxes, and snakes per- 

 sistently seek them in their retreats. 



THE BEACH MOUSE (Peromyscus polio- 

 notus niveiventris and its relatives) 



{For illustration, sec page 428) 



The beach mouse is a beautiful, velvety- 

 furred little creature about the size of a house 

 mouse and one of the smallest species of the 

 genus Peromyscus. Its back is colored with 

 delicate shades of pale vinaceous-buffy and its 

 imderparts, including the feet, are snowy white. 



The species Peromyscus polwnotus, of which 

 the beach mouse is one of several geographic 

 races, or subspecies, occupies a comparatively 

 restricted range in the lowland region of Ala- 

 bama and Georgia and thence through a large 

 part of Florida. 



It presents an unusually convincing illustra- 

 tion of the influence of changing environment 

 upon the physical characters of animals. 

 Among the cotton fields of Alabama and 

 Georgia Peromyscus polionotus is rather dark 

 grayish brown, but on the lighter-colored soil 

 of Florida the color responds and becomes 

 paler in perfect correspondence with the change 

 in soil until the white sand-dunes and beaches 

 of the coast are reached. There, in strong con- 

 trast with the color of the northern members 

 of the species, it is so modified that the pale 

 representatives of this area are recognized 

 under the name niveiventris, as a geographic 

 race, or subspecies. 



Changes in environment affect both great and 

 small mammals in a variety of ways, sometimes 

 in shades of color, sometimes in relative size, 

 and sometimes in proportions. Exceptions to 

 the rule are to be found, however, and some 

 species of mammals have a wide range under 

 a great variety of conditions, with scarcely an 

 appreciable sign of variation. 



The beach mouse is abundant on the sand- 

 dunes and beaches of peninsular Florida, espe- 

 cially from Palm Beach to Mosquito Inlet, 

 wherever there is a growth of sea oats ( Uniola) , 

 which appears to be its principal food plant. 

 It is a nocturnal animal and its nightly activi- 

 ties may be read, early in the morning, from 

 the multitude of tiny tracks which lead in all 

 directions and often form a network on the 

 sand. A single track sometimes extends for a 

 hundred yards or more from a burrow, and 

 with all its windings may aggregate several 

 hundred yards of travel, showing the activity 

 of this small worker during many hours. 



Tracks are most plentiful immediately about 



