ENVIRONMENT, PAST AND PRESENT 85 



there is no reason to exclude individual memory 

 from the migratory performance. There is every 

 reason to believe that it plays an important part 

 with many species, and may account not only for 

 preci^on in the return to a specific locality but, by 

 being superimposed on the inherent "sense of di- 

 rection," for the ultimate modification of migration 

 routes. Young American golden plovers on leaving 

 the barren lands drift south through central Canada. 

 They occur in large numbers all over the plains. 

 Their migration — an initial and instinctive perform- 

 ance — is a south-eastward drift on an enormous 

 front rather than a flight over a well defined route. 

 Adults turn up merely as stragglers. Old-time 

 hunters of the golden plover, such as G. H. Mackay, 

 stress the fact that the huge flocks of birds driven 

 inland by storms from the Atlantic in Massachusetts 

 in September were composed entirely of adults. 

 This species thus presents us with two completely 

 different fall routes, 2000 miles apart. The adults 

 traverse the ocean, the young cross the Canadian 

 plains. We may assume that the latter route is 

 instinctively adopted. Its diffuseness, the fact 

 that the young take it on their first migration in the 

 fall and all American golden plovers use it in the 

 spring, all suggest this. The fall route of the adults 

 might be explicable if we infer that the rich berry 



