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U. S. NATIONAL MUSEUM BULLETIN 217 



were released from the cover of ice. Tliis expansion in distribution 

 and numbers of birds appears favorable for the development of new- 

 populations and their subsequent variation from the species type. 

 It is tempting to hope that in their geographical courses the annual 

 migrations we now observe may show traces of their development 

 which, in relation to climatic history, will recapitulate the kinetics 

 of avian processes of distribution and reveal the geographical in- 

 fluences which assist the differentiation of species into races. It is 

 obvious that I think that the species now migrating to Alaska and 

 Yukon did not remain there during the last ice age, and that they 

 then occupied milder southern territories. The habits and tolerance 

 of cold of most of the migratory species make it unlikely that they 

 had traffic with the Arctic over an ice cap. I do not feel equal assur- 

 ance in speculating upon whether the species now resident in arctic 

 Alaska and Yukon remained in the unglaciated regions while the land 

 to the south was covered with ice, although the hardiness of the 

 present resident land birds makes it plausible that they could have 

 remained if the conditions provided them with food. 



Table 8. — Ranges of birds present in winter 



[Explanation— (P) presence established. American range: (A) Alaska, (Y) Yukon, (M) northwest 



Mackenzie.] 











Kange 



Species 



Anak- 

 tuvuk 



Kobuk 



Old 

 Crow 





















World 



American 



Accipiter gentilis atricapillus 





P 



P 



Eu As Am 





Falco rasticolus obsoletus 



P 



P 



P 



Eu As Am 





Canachites canadersis osgoodi 





P 



P 



Am 



AYM 



Bonasa umbellus yukonensis 







P 



Am 



AYM 



Lagopus lagopus alascensis 



P 



P 



P 



Eu As Am 



AYM 



Lagopus mutus nelson! 



P 



P 



P 



Eu As Am 



AYM 



Bubo virginianus lagophonus 



P 



P 



P 



Am 



AY 



Nyctea scandiaca 



P 



P 



P 



Eu As Am 





Sumia ulula caparoch 





P 



P 



Eu As Am 





Strix nebulosa nebulosa 





P 



P 



Eu As Am 





Aegolius funereus rlchardsoni 



P 



P 



P 



Eu As Am 





Dendrocopos pubescens nelsoni 



P 



P 





Am 





Picoides arcticus 





P 





Am 





Picoides tridactylus fasciatus 



P 



P 



P 



Eu As Am 





Corvus corax principalis 



P 



P 



P 



Eu As Am 





Perisoreus canadensis pacificus 



P 



P 



P 



Am 



AYM 



Parus atricapillus tumeri 



P 



P 





Am 



A 



Parus cinctus lathami 





P 



P 



Eu As Am 



AYM 



Parus hudsonicus hudsonicus 





P 



P 



Am 





Cinclus mexicanus unicolor 



P 



P 



P 



Am 





Bombycilla garrula pallidiceps 





P 



P 



Eu As Am 





Pinicola enucleator alascensis 



P 



P 



P 



Eu As Am 



AYM 



Aeanthis homemanni exilipes 



P 



P 



P 



Eu As Am 





Acanthls flammea flammea 





P 





Eu As Am 





Loxia leucoptera Icucoptera 





P 



P 



Eu As Am 





Total (25) 



(13) 



(24) 



(21) 





