ward migration." Demonstration of this phenomenon is especially 

 important as it relates to locality-faithfulness (Ortstreue), range 

 extension, and gene mixture between populations. These movements 

 cannot be considered as true migrations even though they are 

 repeated annually by the species between breeding grounds and 

 some other area. These movements are generally repeated by the 

 same age class in the population but not the same individuals. 



Nevertheless, these regular northward movements are quite 

 striking, especially in herons. The young of some species commonly 

 wander late in the summer and fall for several hundred miles north 

 of the district in which they were hatched. Young little blue herons as 

 well as great and snowy egrets are conspicuous in the East as far 

 north as New England and in the Mississippi Valley to southeastern 

 Kansas and Illinois. Black-crowned night herons banded in a large 

 colony at Barnstable, Massachusetts, have been recaptured the same 

 season northward to Maine and Quebec and westward to New York. 

 In September most of them return to the south. 



These movements have been noted in several other species as well. 

 Broley (1947) nicely illustrated this northward movement of bald 

 eagles along the Atlantic coast (Fig. 29). Birds banded as nestlings in 

 Florida have been retaken that summer 1,500 miles away in Canada. 

 Van Tyne and Berger (1959) surmised the summer heat of Florida 

 was too great for this eagle, a northern species that has only recently 

 spread into Florida to take advantage of abundant food and nesting 

 sites, which it exploits during the cooler season. Postbreeding 

 northward movements are also shared by wood ducks, yellow- 

 breasted chats, eastern bluebirds, and white pelicans. 



A somewhat different type of postbreeding migration is the so- 

 called "molt migration" exhibited by many species of waterfowl 

 (Salomonsen 1968). These birds may travel considerable distances 

 away from their nesting area to traditional molting sites where they 

 spend the flightless period of the eclipse plumage. At such times they 

 may move well into the breeding ranges of other geographic races of 

 their species. These movements may be governed by the availability 

 of food and are counteracted in fall by a directive migratory impulse 

 that carries those birds that attained more northern latitudes after 

 the nesting period, back to their normal wintering homes in the 

 south. 



Vagrant Migration 



The occasional great invasions beyond the limits of their normal 

 range of certain birds associated with the far North are quite 

 different from migration patterns discussed previously. Classic 

 examples of such invasions in the eastern part of the country are the 

 periodic flights of crossbills. Sometimes these migrations will extend 

 well south into the southern States. 



Snowy owls are noted for occasional invasions that have been 

 correlated with periodic declines in lemmings, a primary food 

 resource of northern predators. According to Gross (1947), 24 major 



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