OLD CROW 241 



explanations of the oversized weights. They show the expansive 

 capacity of avian metabolism for egg laying, the adequacy of the 

 food supply, and imply that the individuals were secure for an ex- 

 panded feeding program in a social system organized to preserve 

 individuals from stress during the period of reproduction. This view 

 goes with the appearance of leisurely behavior among the birds, at 

 least until the nestlings must be often fed. 



The fact that no casualties were observed among the eggs or 

 nestling birds suggests that reproductive efficiency was high in this 

 rather dense population of fox sparrows, which went through its re- 

 productive cycle with such amazing speed. 



Since some of the patterns of individual breeding behavior were 

 compressed within such short intervals, it seems quite likely that the 

 contributory development of some physiological changes was acceler- 

 ated. The duration of incubation and of nestling growth are not to 

 be suspected of being much influenced by the environment for they are 

 ancient characters of species and even higher systematic relations 

 (Irving and Krog, 1956). The conspicuous modification in arctic 

 breeding occurs in the synchrony of the stages in the entire population, 

 as Barbara Oakeson has so clearly shown in Alaskan Gambel's spar- 

 rows (Oakeson, 1954). That this synchrony greatly reduces strife 

 and promotes social order is undoubtedly a factor of advantage for 

 the economy of arctic nesting, and the resultant short period devoted 

 to breeding in the Arctic must further reduce the social and physical 

 stress which birds encounter during the longer breeding seasons of 

 warmer climates. Because of its apparent advantages, the synchrony 

 of the progress of arctic birds through their arctic breeding cycle 

 can be regarded as an adaptation. This viewpoint is discussed in 

 detail in chapter 7. 



Fox sparrows of the race zaboria winter mainly east of the Missis- 

 sippi. Their northern nesting range reaches the Arctic only in Mac- 

 kenzie, Yukon, and Alaska. They are the only species of the Fringil- 

 lidae nesting there which can be called eastern in reference to their 

 wintering range, and yet they, with gray-cheeked thrushes and some 

 wood warblers, also eastern wintering races, migrate from near ex- 

 treme southeastern to extreme northwestern parts of North America 

 to nest. 



Melospiza lincolnii lincolnii (Audubon) 



1 male May 31 weight 19.1 g. little fat testes 5x10, 8x10 mm. 



Francis Williamson heard the male Lincoln's sparrow singing in 

 the rank grassy clearing by the Eoman Catholic Mission and collected 

 the only record of its occurrence at Old Crow. The bird acted as if 

 it had assiuned a territory. It has been identified at Forty Mile 

 (Grinnell, 1909) , found sparsely along the Yukon River west of the 



