RAPIDITY OF MIGRATION MOVEMENT 115 



are quieter than in spring and more difficult to ob- 

 serve. The journey in many cases also is irregular 

 and prolonged. We may look to data secured from 

 bird banding to give more definite information as to 

 the rapidity of migratory movement in individual 

 birds, and we shall turn to that source especially for 

 the movements of autumn migrants when sufficient 

 records have been amassed. 



Distances travelled by Migrants 



The length of the migration route is a highly vari- 

 able factor, depending upon local conditions and the 

 species of bird concerned. In the mountains of Him- 

 alaya, as winter approaches, the snow partridge may 

 descend a few hundred feet in altitude, to a winter 

 ground, merely by travelling a mile or two, or, in 

 this country, the long-tailed chickadees of the Rocky 

 Mountains may drop down from the aspen groves at 

 8,000 feet, where they have nested, to creek bottoms 

 a few miles distant in the foothills. Flights that may 

 be covered in a few minutes place these birds in 

 regions where they find conditions suitable to their 

 needs for winter. We may contrast these flights 

 with that of the Arctic tern, which nests in the most 

 northern land known (the first nest discovered is 

 said to have been only 450 miles from the North 

 Pole) and which spends the winter in seas skirting 

 the Antarctic continent, with an air line 1 1,000 miles 



