HAMILTON: MAMMALOGY IN NORTH AMERICA 679 



use of each whale taken. The participating nations, which include most of the 

 important whaling countries, share responsibility for enforcement (Carson, 1948). 

 The history of the beaver in North America follows a pattern well known to 

 conservationists. At one time it was widespread and abundant in the east but 

 trapping pressure for the valued pelts brought it virtually to the brink of exter- 

 mination. By 1900 New York and the New England states could boast of only 

 a few dozen. Introductions of a few here and there resulted in an astonishing 

 increase. In the early 'twenties, increasing complaints of damage indicated all 

 too well the success of these introductions. The beaver is now actually a pest in 

 many of the regions where it was a rarity a half-century ago. Through the lElood- 

 ing of valuable timberland this big rodent may actually prove a nuisance. The 

 white-tailed deer is another striking example of a species that became so scarce 

 in the early part of the present century that Easterners considered it no longer 

 of significance as a game species. Introductions and closed seasons have now 

 made this fine animal abundant in the East. Its unprecedented increase in recent 

 years has been cause for much concern among agriculturists, for deer depredation 

 in orchards and to crops is of no mean consequence. 



Some Practical Considerations 



With increasing human populations, it was apparent that the wildlife of North 

 America would play an ever more important role. Environmental changes 

 wrought by man resulted in far-reaching effects. Lumbering operations destroyed 

 habitat for the moose and bear, while it created a more desirable habitat for the 

 cottontail and fox. The resultant farmlands and second-growth timber provide a 

 more suitable environment for many species that shun the solid stands of timber. 

 Destruction of grasslands on the western prairies increased competition between 

 rodents and livestock for the range. These changes have been reflected in many 

 ways. 



It is difficult, often impossible, to assess an animal in the economic ledger. The 

 common field mouse plays a useful part in the economy of nature when it occupys 

 waste lands. Here it provides food for a host of predators, transforming grass 

 into fur coats. It may act as a buffer against predation on more desirable species. 

 In the orchards and grain fields, its ravages are measurable; here it must be 

 classed as a pest of the first order. We acknowledge the usefulness of the beaver 

 in impounding waters and preventing rapid run-off. Its value in the past and 

 present as a fur-bearer will not be denied. When the big rodent kills extensive 

 tracts of valuable timber through flooding, or disrupts a water supply through 

 interference with the normal water level, then we must take steps to control the 

 animal. The cottontail rabbit is hailed as our primary game animal in the eastern 

 states, yet its depredations in the orchard or garden are often severe. It must 

 now be apparent that a decision regarding the economic value of a species is 

 difficult, indeed, often impossible, in the light of our present knowledge. Judg- 

 ment of any species must take into consideration many factors, two of the most 

 important being time and place. 



We may consider several categories, when attempting a critical judgment of 

 the economic worth of a species. 



