as chicks at colonies in the Great Lakes have scattered in all directions 

 after the breeding season, some having been recovered well north in 

 Canada. 



These movements may be considered as migration governed only by 

 the availability of food, and they are counteracted in fall by a directive 

 migratory impulse that carries back to their normal winter homes in 

 the south those birds that after the nesting period attained more 

 northern latitudes. They are not to be compared with the great in- 

 vasions of certain birds from the North. Classic examples of the latter 

 in the eastern part of the country are the periodic flights of crossbills. 

 Sometimes these migrations will extend well south into the Carolinian 

 Zone. 



Snowy owls are noted for occasional invasions that have been corre- 

 lated with the periodic maximum of Arctic foxes and the lemming 

 cycle in the north. According to Gross (1947) 24 major invasions 

 occurred between 1833 and 1945. The interval between these varied 

 from 2 to 14 years, but nearly half (11) were at intervals of 4 years. 

 A great flight occurred in the winter of 1926-27 when more than 1,000 

 records were received from New England alone, but the largest on 

 record was in 1945-46 when the "Snowy Owl Committee" of the Amer- 

 ican Ornithologists' Union received reports of 13,502 birds, of which 

 4,443 were reported as killed. It extended over the entire width of the 

 continent from Washington and British Columbia to the Atlantic coast 

 and south to Nebraska, Illinois, Indiana, Pennsylvania, and Maryland. 

 One was taken as far south as South Carolina. 



In the Rocky Mountain region great flights of the beautiful Bohemian 

 waxwing are occasionally recorded. The greatest invasion in the his- 

 tory of Colorado ornithology occurred in February 1917, at which time 

 the writer estimated that at least 10,000 were within the corporate 

 limits of the city of Denver. The last previous occurrence of the species 

 in large numbers in that section was in 1908. 



Evening grosbeaks likewise are given to performing more or less 

 wandering journeys, and curiously enough, in addition to occasional 

 trips south of their regular range, they travel east and west, sometimes 

 covering long distances. For example, grosbeaks banded at Sault 

 Ste. Marie, Mich., have been recaptured on Cape Cod, Mass., and in the 

 following season have been retrapped at the banding station. Banding 

 records demonstrate that this east-and-west trip across the northeastern 

 part of the country is sometimes made also by purple finches. 



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