42 GAME BIRDS OF CALIFORNIA 



A modification of this method, which consists in retaining the birds 

 under semi-wild conditions until they have been partially acclimated, 

 would probably produce still more satisfactory results; but this and 

 many other feasible experiments have not been systematically tried 

 out. 



The liberation of birds which have been propagated in captivity 

 almost always results in failure. The successful maintenance of 

 foreign species in aviaries is no test of their ability to establish and 

 maintain themselves when released in the wild. Unless birds reared 

 on a game farm can be brought up under serai- wild conditions nothing 

 but unfavorable results are to be expected when they are liberated. 

 The complete change that occurs, in the nature of their food and their 

 method of procuring it, and the presence of enemies which they have 

 not encountered in captivity, are circumstances which birds that have 

 been propagated under artificial conditions cannot be expected to 

 contend with successfully. Failure to recognize these principles has 

 made many attempts at acclimatization unsuccessful. A state game 

 farm can be of value to game breeders as an experiment station for 

 testing the practicability of methods of rearing game in captivity; 

 but its service as a means of rearing birds suitable for liberation in 

 the wild has yet to be demonstrated in this state or elsewhere. 



Here, then, are the factors of climate, of food, of safe breeding 

 places, and of safe cover from enemies, conditions that must be con- 

 sidered when an attempt to introduce an exotic species is made. These 

 are precisely the same factors which prevent the spread of a species 

 beyond a certain normal boundary, and they affect its persistence in 

 like degree when it is transplanted to a new locality. There are 

 doubtless many foreign species that possess an inherent ability to 

 adapt themselves to one of the changed conditions represented among 

 these factors ; but the possibility of finding a species which can adapt 

 itself to all of the changed conditions is extremely small. With the 

 increase in the number of limiting factors there is a decrease in the 

 number of species capable of successfully meeting all of them. Few 

 species can ever be considered as candidates for introduction into any 

 one new locality. 



The possibility of failure is not the only objection to projects 

 of introducing foreign game birds. Three others are yet to be men- 

 tioned: the possibility that the species introduced may later become 

 undesirable ; that it may completely replace some native species ; and 

 that it may bring in some infectious disease such as will spread to 

 native species. No instance of the introduction of a wholly unde- 

 sirable species of game bird is known to us, but the conspicuous cases 

 of the English Sparrow and Starling among small birds should warn 

 us of grave consequences in this connection. * 



