SMALLER MAMMALS OF NORTH AMERICA 



By Edward W. Nelson 



Chief, U. S. Biological Survey 



With illustrations in color from paintings by Louis Agassia Fiicrtcs 



IN THAT part of North America 

 lying north of Mexico more than 

 1,300 species and geographic races 

 of mammals are known to exist. Of 

 these by far the greater number, both of 

 species and individuals, fall into the class 

 of smaller mammals. 



Some of the most characteristic types 

 which appear to have originated in North 

 America are the mountain - beavers, 

 pocket-gophers, kangaroo-rats, pocket- 

 mice, wood - rats, white - footed mice, 

 muskrats, skunks, and ring-tailed cats. 



In Siberia and Europe live close coun- 

 terparts of our northern weasels, minks, 

 martens, field - mice, lemmings, north- 

 ern hares, conies, marmots, moles, and 

 others ; and on our southern border the 

 armadillo and the hog-nosed skunk intro- 

 duce a faint tinge of a strange fauna 

 from South America. 



FURRY FRIENDS AND CNFMIFS 



The muskrats, minks, martens, and 

 skunks for many years have yielded an 

 enormous annual return from their furs ; 

 the squirrels and rabbits afiford sport and 

 a large supply of excellent flesh for food ; 

 the prairie-dogs and some of the ground- 

 squirrels existing in enormous numbers 

 have been excessively destructive to 

 crops ; and others, like the porcupine and 

 the armadillo, have attracted particular 

 attention because of their strange char- 

 acteristics. 



ANIMALS THAT LEARNED TO "dIG IN" 



The smaller mammals live everywhere, 

 from the tropical end of Florida to the 

 uttermost lands of the frozen North, and 

 from the seashore to the limit of vegeta- 

 tion on the high mountains. The heav- 

 iest forests, open meadows, rugged moun- 

 tain slopes, arctic barrens, and sun- 

 scorched desert plains all have their small 

 four-footed habitants. INTany modifica- 

 tions of parts and organs of the various 

 species have been necessary to adapt the 

 small mammals to specialized modes of 

 life. 



This is strikingly illustrated in the case 

 of those true rodents, the pocket-gophers, 

 which apparently found competition on 

 the surface of the ground so acute that 

 they took the unoccupied territory below 

 the surface, where they live as miners 

 and tunnel from place to place in search 

 of edible roots, with an occasional stealthv 

 excursion above ground to seize some of 

 the food available there. 



Another excellent illustration is fur- 

 nished by the moles, which, leaving the 

 numerous closely related species — the 

 shrews — to feed upon insects above 

 ground, have descended and, like the 

 pocket-gophers, live in tunnels which they 

 make in the pursuit of earthworms and 

 insects below the surface ; like the go- 

 phers, they, too, make occasional excur- 

 sions above ground in search of food. 



The mink and the muskrat, represent- 

 ing the carnivores and rodents, have 

 rivals for their food supply on land and 

 have become amphibious, being as much 

 at home in the water as on shore, one 

 feeding on fish and flesh and the other on 

 aquatic vegetation. Certain forms of the 

 squirrel tribe are heavy-bodied and live 

 in underground burrows, while other 

 more slender and graceful species make 

 their homes in the tree-tops. 



A DEPARTURE FOR EVERY NEED 



Another member of this group, the fly- 

 ing-squirrel, has developed an extension 

 of the skin uniting the front and hind 

 legs, so it may glide freely from tree to 

 tree. The bats have gone still further, 

 and the skin uniting their lengthened 

 front and hind limbs and long finger 

 bones forms broad wings which lend 

 them powers of flight scarcely equaled by 

 those of l)irds. 



The gophers, pocket-mice, chipmunks, 

 and others are provided with little cheek 

 pouches in the skin on each side of the 

 mouth, in which they may carry food 

 home to their store-rooius and otlier hid- 

 ing places. 



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