distances east and west to reach the western edge of the route 

 followed by the bulk of the bobolinks that breed in the northern 

 United States and southern Canada. 



During the past few decades, various populations of Canada geese 

 have altered their migration patterns as a result of transplanting 

 brood stock, development of refuges or changing agricultural 

 practices. These routes will continue tachange in the coming years as 

 long as these factors are in a state of flux. It has been shown 

 that man can establish breeding colonies of Canada geese with young 

 birds almost anywhere. 



Europe also has several good examples of changes in migration 

 routes through range extension. One of the best examples is the serin. 

 During the past century, this European finch has spread its breeding 

 range from around the Mediterranean Sea to include the entire 

 continent. While the Mediterranean populations remain sedentary, 

 the more northern breeding birds are migratory. Most likely, those 

 birds that did not migrate from the North were eliminated by severe 

 weather. Similarly, the wheatear, yellow wagtail, and Arctic 

 warbler have extended their breeding ranges eastward across the 

 Bering Sea into Alaska, but the wheatear, for instance, migrates all 

 the way back across Asia to Africa where it winters with other 

 wheatears coming from Europe, Iceland, and Greenland. 



As bird populations become more and more migratory, we might 

 expect their flight capabilities to be enhanced accordingly. These 

 changes in morphology are readily seen in wing shape. Several 

 groups of birds have closely related species or populations some of 

 which are migratory and others sedentary. The sedentary species or 

 populations have more rounded wings because of the relative length 

 of the wing quills. On the other hand, populations that migrate great 

 distances, such as albatrosses, falcons, swifts, various shorebirds, 

 and terns, have more pointed wings. Kipp(1942, 1958) demonstrated 

 this using orioles. The sedentary black-headed oriole of India has a 

 well-rounded wing whereas the closely related black-naped oriole is 

 migratory between India and Siberia and has primaries that are 

 much more pointed and well developed. 



Thus it seems the origin and evolution of migration have roots in 

 the present that are deep in the past. The important thing to consider 

 in the evolution of a migratory trait is whether a population can adapt 

 to new conditions by genetic modification of its physiology and 

 habits. The migratory habit has evolved in those populations in 

 which, on the average, more individuals survive by moving to a 

 different area part of the year than if they remained in the same area 

 all year. 



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