VANISHING SPECIES 335 



so many foxes, dogs, mink, men, and raptorial birds. In 

 the Western States the rabbits have lately increased 

 to such an extent that public drives or hunts are arranged, 

 by which as many as twenty thousand are taken in a single 

 day. This increase is due to the fact that the wolves and 

 coyotes, which formerly preyed on the rabbits, have year 

 by year had their ranks lessened by the shotgun, the trap, 

 and poisoned bait. In parts of New Zealand, where car- 

 nivorous animals are few, the imported rabbits have multi- 

 plied to such an extent as to consume all the grass, thereby 

 causing the sheep to starve to death. Thus the ascendency 

 of one group of animals often means the disappearance of 

 another. This is especially true of the introduction of a 

 parasite into a new country where the hosts have not be- 

 come more or less adapted to withstanding its attacks. 

 The smallpox germ introduced into Iceland in 1734 killed 

 more than half the population, and almost equally fatal 

 results occurred when the disease first visited Greenland. 



It is therefore evident that the extermination of a species 

 depends on several factors, most important of which are 

 the presence of numerous enemies and the lack of proper 

 food. During the age of man, including perhaps not much 

 over a hundred thousand years, several species of verte- 

 brates have become extinct, among which are the huge 

 mammoth (a near relative of the elephant), Steller's sea 

 cow, the great auk, and the moas or giant birds of New 

 Zealand. 



In 1871 Colonel Dodge drove for twenty-five miles along 

 the Arkansas River through an unbroken herd of buffalo. 

 Millions of these noble animals fed on the western plains. 

 A few years later the completion of the Northern Pacific 



