IRREGULAR MIGRATION 95 



the border and invades the isolated mountain chains 

 of southern Arizona, where it has been reported on 

 several occasions from the Chiricahua Mountains, 

 and more recently, in 1917, from the Huachuca, 

 Dragoon, Graham, and Galiuro ranges. The birds 

 appear in late summer in roving bands that may 

 include several hundred individuals. 



In July, 1917, such an invasion came in the south- 

 ern Chiricahua Mountains, and by August had pene- 

 trated to Pinery Canyon at the north end of the 

 range. Mr. Frank Hands, a close observer, informed 

 me that he was certain from the condition of their 

 plumage that many were young which had been 

 hatched that year. The birds remained here through 

 the winter, feeding early in the season on cones of 

 the Chihuahua pine {Pinus chihuahuana) ^ and when 

 these were gone, on the acorns of various species of 

 oaks. By November they had decreased in abun- 

 dance, but a few remained until March, 191 8; in 

 May of that year a few appeared in the Galiuro 

 Mountains farther north, and remained until early 

 autumn. 



The flights of birds that have been mentioned 

 have been a puzzle to naturalists from the irregular- 

 ity of their occurrence, and have been explained on 

 the hypothesis of failure of food supply, increase in 

 numbers beyond the capacity for support of the nor- 

 mal range, and severe cold. Failure of food seems 



