THE DANGEK OF INTRODUCING NOXIOUS ANIMALS 



AND BIRDS. 



By T. S. Palmer, 

 Assistant Chief of Biological Survey. 



INTRODUCTION. 



Acclimatization of plants and animals lias attracted attention in 

 all parts of the world. Usefnl or enrious species have been intro- 

 duced from one country to anotlier with varying degrees of success; 

 some have failed while others have become acclimated, and occa- 

 sionally have increased to such an extent as to usurp the places of 

 native species. In comparing the results of the introduction of 

 plants and of animals, the important difference between these two 

 classes of experiments should not be lost sight of. Plants, on the one 

 hand, are introduced almost without exception for purposes of cultiva- 

 tion, and are therefore kept somewhat under control. Occasionally, 

 under favorable conditions, they ' ' escape " and increase so rai)idly that 

 they become troublesome weeds. Chicory and wild garlic of the 

 Eastern States and the water hyacinth of Florida are familiar exam- 

 ples of weeds originally introduced as useful or ornamental plants. 

 Animals, on the contrary, unless intended for pets or for exhibition 

 in menageries or zoological gardens, are seldom kept in captivity, 

 but are liberated and allowed to live as nearly as possible under nat- 

 ural conditions. Only the strongest and hardiest species survive, 

 and in adapting themselves to new surroundings necessarilj- cause 

 some change in the existing fauna. If prolific, they are likely to 

 become abundant in a short time; if they crowd out indigenous spe- 

 cies, they are regarded as nuisances. Hence, it is sometimes said that 

 acclimatization ot animals has produced far less satisfactory results 

 than that of plants, but the comparison is made between the relatively 

 small number of animals, birds, and insects purposel}* imported and 

 allowed to run Avild and a long list of useful and ornamental plants 

 carefully kept under cultivation. 



MEANS OF DISPERSAL. 



Animals are transported from one country to another or to distant 

 islands either hy accident or by the direct agency of man. Horses, 

 cattle, sheep, goats, pigs, dogs, and cats are now almost cosmopolitan, 

 but they owe their wide distribution entirelj^ to man, who has carried 

 them with him to all parts of the earth. Accidental distribution is 



