94 THE MIGRATIONS OF BIRDS 



Mountain region, as well as the ordinary form from 

 the north, indicating a migration from the moun- 

 tains out across the plains. From this it appears that 

 these movements may be true wandering without 

 definite direction. In the winter of 191 6 there oc- 

 curred an irruption of the white-winged crossbill 

 that brought these birds south as far as the city of 

 Washington, where the species, though rare, has 

 been found occasionally in the summer season. 



At irregular intervals too come great flights of 

 goshawks that spread across the entire northern 

 half of the United States, and penetrate south to 

 California and New Mexico. During a recent irrup- 

 tion the eastern form of this bird was recorded west 

 across the Rocky Mountains into California, thus 

 covering the usual range of the western form. The 

 coming of hordes of this predatory bird is fraught 

 with danger to the ruffed grouse of Michigan, Wis- 

 consin, and the New England States, as the hawks 

 hunt the grouse relentlessly, and have on occasion 

 reduced these game birds almost to extinction. With 

 the goshawks often there arrive many snowy owls 

 and unusual numbers of great horned owls. 



As irregular movement in a northern direction I 

 may cite the case of the thick-billed parrot {Rhyn- 

 chopsitta pachyrhyncha) ^ resident regularly in the 

 mountains bordering the Mexican Tableland, which 

 at intervals of a number of years comes north across 



