SPEED OF THE ROBIN MIGRATION 

 (Reproduced by permission of the Biological Survey from W. W. Cooke's 'Some New Facts About the 

 Migration of Birds,' Year boolc, Department of Agriculture, 1903, pp. 371-386.) 



The black band indicates the average position of the isotherm of 35° F. at the several dates men- 

 tioned. The dotted band shows the approximate route of the Robins of northwestern Alaska. The dates 

 in this band represent the average time of arrival of the earliest Robins. The numbers at the side of the 

 migration route indicate in miles per day the average speed of migration between the dated places. 



(57) 



