298 



U. S. NATIONAL MUSEUM BULLETIN 217 



casional comparisons, indicate that winter temperatures in the nar- 

 row mountain valley at Anaktuvuk do not reach the extreme lows 

 measured in the broad valleys at lower elevations at Umiat, Bettles, 

 and Fairbanks. It appears that the mean monthly temperatures in 

 spring at Anaktuvuk lie between those of Umiat and Bettles. Be- 

 tween March and June the mean temperature at Anaktuvuk rises 

 from about -20° C. to about +10° C. 



20 



10- 



-10- 



ZO' 



=3 0- 



SEATTLE 

 O 



JAN 



FEB 



MAR 



APR 



MAY 



JUNE 



Figure 14. — ^Winter to summer progress of monthly mean temperatures in three Alaskan 

 localities and in three northern States. 



During the days before and after May 20, when most migrant bird 

 species first reach Anaktuvuk, the mean temperature of the air is 

 just above freezing. Migratory birds can be regarded as land birds 

 at Anaktuvuk in the sense that they feed on snow-free ground or in 

 shallow pools and waters free of ice. This requirement of unfrozen 

 feeding ground is probably common for most of the birds migrating 



