RESIDENCE IN THE ARCTIC 299 



into arctic and boreal regions. It does not limit the advent of birds 

 predatory upon mammals or feeding upon carrion, seeds, and insects 

 in exposed vegetation. Eagles, rough-legged hawks, snow buntings, 

 and longspurs precede the appearance of water and snow-free ground. 

 But for most species of migrants water and unfrozen ground seem 

 to be the main feeding places. 



Although brought about by solar heat, the breakup of ice on large 

 rivers is also influenced by the thickness of winter ice and snow and 

 by the amount of water impounded at the time of the autumn freeze- 

 up. The date of the breakup of the Koyukuk River near Bettles 

 has been observed at various dates from early to late May. In 1949 

 and 1952 small airplanes could land on wheels on the ice of lakes 

 at Anaktuvuk until mid-June. In 1951 the ice was insecure in late 

 May and Pilot J. L. Anderson landed with us on floats before the 

 end of May. The complete breakup of ice is too variable and ill- 

 defined to use in dating a phenomenon which appears with such 

 regularity as bird migration. These events are all related to the in- 

 creasing heat of the sun, but not by obvious, simple parameters. 



Heavy arctic snow cover in May would appear to be a handicap 

 to birds migrating from the south. In 1952 snow was unusually deep 

 over the mountain valleys and along the Koyukuk until the end of 

 May. In 1950 and 1953 most of the ground was bare early in that 

 month. The dates when the ground is mostly free from snow may 

 differ by 3 or 4 weeks in successive years. 



In May the arctic land vegetation shows little change that could 

 be significant for birds. The first pollen appears on willows at the 

 end of the month, when a few bumblebees are seen. Early flowers 

 of sedge serve ptarmigan and caribou but seem to afford no sustenance 

 for most migratory birds. In short, the spring outburst of land 

 vegetation is considerably preceded by the advent of the birds. 

 Farther south at Bettles and Fairbanks the emergence of birch leaves 

 is a conspicuous and rather sudden event. I know of no published 

 records, but my memory of the events of spring and examination of 

 the recollections of old observers indicates that the emergence of 

 birch leaves in interior Alaska may differ by as much as two weeks 

 from one year to the next. It commonly follows the arrival of most 

 migratory birds. 



The spring progress of arctic and subarctic vegetation is scarcely 

 visible when the main migration occurs. I have not noticed many 

 seeds of flowering plants at any time in the Arctic and I suspect that 

 they are not abundant in spring. During May flying insects are 

 rare and few can be discovered moving on the ground. Terrestrial 

 arthropods could have been little influenced to new growth in the 

 arctic spring when the birds arrive and those serving as food for birds 



