10. — Retrospect 



Observations during 12 years in northern Alaska have conjSrmed 

 my original opinion that Anaktuvuk Pass would be an ideal location 

 for studying the adaptation of animal populations to arctic life. 



The Pass acts as a funnel through which move the bulk of the ter- 

 restrial vertebrate fauna of the region each spring and autumn, and 

 it also provides breeding sites and environment for many species. 

 It was the easily visible movement of birds and the obvious nature 

 of their biological purposes that lead me to deal primarily with 

 them, and to study them in other localities which, together with 

 Anaktuvuk, would illustrate their adaptation to all of interior arctic 

 Alaska and Yukon. In the prosecution of these studies, the native 

 peoples of the Arctic have played an important role. Their hos- 

 pitality has greatly eased the burden of working in remote regions, 

 while their extensive knowledge of the movements of the various 

 birds has helped me to distinguish the regularity common to popula- 

 tions from the deviations of occasional individuals. 



I have fomid by observations in the field that the physiological 

 condition of birds can be correlated with season and behavior. Many 

 arctic nesting populations of migratory birds arrive fat after rapid 

 flights from distant wintering places. Each species arrives on its 

 own schedule. The individuals are in similar physiological prepara- 

 tion for breeding; they promptly separate into pairs and produce 

 young which grow to adult size; and then as individuals the parents 

 and young rejoin the populations ready to migrate southward. 

 Within each population the physiological states of individuals are 

 synchronized and the dependent social processes keep each population 

 distinct and in order, with little apparent conflict. 



It is evident that the cycle of migration and nesting is physiologi- 

 cally anticipated and that the anticipatory processes are correlated to 

 meet the normal progress of the seasons. Normal seasonal cycles 

 vary geographically and have changed even in historic times. As 

 demonstrated in the early chapters, the geographical and temporal 

 extent of my observations have made possible an analysis of the kind 

 and degree of correlation that must exist between the lives of birds 

 and the environment in which they live. For many parts of the 

 world, the factors involved in such an analysis are so numerous and 

 their variations often so subtle that it would be difficult to develop 



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