BIOLOGICAL ASPECTS 329 



teresting studies developed the evidence for the proposition that races 

 of Pacific Coast white-crowned sparrows destined to make long mi- 

 gratory flights northward became fat in the period before departure 

 while races preparing for only a short migratory flight accumulated 

 little or no fat before the event. 



Mrs. Oakeson has kindly sent me figures recording the weight and 

 fatness of examples of the race of white-crowned sparrows examined 

 by her just before leaving their California wintering ground and by 

 McCabe at a station in British Columbia more or less in midcourse 

 of migration. At both places the sparrows were generally heavy and 

 commonly fat. When members of this race were taken after arrival 

 on their breeding ground at Mountain Village, Alaska, they were 

 lighter and less fat than in the early stage of the migration through 

 Santa Barbara, California (Oakeson, 1953). The average weight of 

 7 males in May at Mountain Village was 25.8 grams. At Anaktuvuk 

 25.6 grams was their average weight during the summer, but during 

 the first week after arrival the males were about 5 percent heavier. I 

 conclude from Mrs. Oakeson's records that in April when this race 

 started migration through California their average weight was as 

 much as 20 percent greater than after their settlement on their Alaskan 

 breeding grounds. A decline in weight of birds on the nesting ground 

 appears to occur soon after arrival, but I suspect that some migrants 

 start to lose weight during the last stages of their northern flight. 



In several species at Anaktuvuk the females did not appear to lose 

 weight until after their eggs had hatched. This contrast between the 

 sexes conforms with the intense activity of male birds after they 

 arrive, while courting and maintaining their nesting territories. This 

 period does not appear to involve the female birds in especially in- 

 tense activity, for they take life easily during mating and incubation. 

 During the mating season the males may even be too busy to eat well. 

 Their fat, which is certainly not completely used up during migra- 

 tion, could serve them well on the breeding ground in the way that 

 reserves of fat enable male fur seals and bull caribou to neglect feeding 

 in order to devote their time exclusively to the jealous watchfuhiess 

 and demonstrations by which they seek to secure their paternity in 

 the offspring of their mates. 



