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THE NATIONAL GEOGRAPHIC MAGAZINE 



Photograph by Howard Taylor Middleton 



IT IS NOT VANITY WHICH PROMPTS THIS MOUSE) TO TAKE) ITS OWN PICTURE: 



The bait is a grain of corn attached to one end of a thread; the other end operates the 

 camera shutter; but the pose is almost "studied" 



abundant, if food becomes scarce they 

 sometimes make extended migrations, 

 during which vast numbers swarm across 

 the country, like the lemmings of the 

 North or the gray squirrels during their 

 historic migrations of early days in the 

 eastern United States. At such times vast 

 numbers of the wandering hordes perish ; 

 epidemic disease also plays its part in re- 

 ducing their numbers. Nature thus is 

 self-limiting in restraining the permanent 

 increase of any species beyond the num- 

 bers needed to preserve its balance. 



The advent of man in new regions with 

 his clearing of forests, cultivation of the 

 soil, and destruction of animal life for 

 food or other purposes, quickly upsets 

 the balance of nature, and some species 

 are much reduced in numbers or disap- 

 pear, while others, especially among the 

 smaller kinds of mammals, may greatly 

 benefit through added food supplies, and 

 then increase until they become a pest, to 



be destroyed by the farmer as a measure 

 of self-protection. 



ANIMALS THAT SEEK SAFETY IN DARKNESS 



For some reason, perhaps owing to 

 their small size and defenselessness 

 against birds and beasts of prey, the great 

 majority of small mammals, including 

 hundreds of species and untold millions 

 of individuals, are nocturnal or live such 

 obscure and hidden lives they are un- 

 known except to the comparatively few 

 people who go much afield, with all their 

 powers of observation alert by day and by 

 night. Many of the mainly nocturnal spe- 

 cies pursue minor activities by day, where 

 shelter of one kind or another gives them 

 a reasonable feeling of security. 



Under the revealing light of day most 

 small mammals, especially the rodents, 

 are extremely watchful and timid, lead- 

 ing lives filled with alarms which com- 

 monly end in tragic deaths. By night 



