50 NOKTH AMKRIGAN FAUNA. [so. 19. 



shore ])irds, or an3"thing on which they could feed. This was very 

 diflferent from the constantly passing- flocks I saw on the Yukon Delta 

 August 27-28, and the abundance of Limicohe at St. Michael in Sep- 

 tember. The smaller land ])irds we often saw late in July and in 

 August. They were usually in family parties, and most of them 

 seemed to be traveling up the river. At Circle the intermediate 

 sparrow, western tree sparrow, and western savanna sparrow were 

 abundant, and were evidently migrating August 19-20. 



Forty-two species of migratory l)irds, exclusive of those possessing 

 a continental range, certainly occur as summer residents in the Yukon 

 Basin above Fort Yukon. Of these, 13 (31 per cent) have their center 

 of distribution in eastern North America, 11 (33 per cent) near the 

 Pacific coast, and 15 (36 per cent) in western North America not far 

 from the Rocky Mountains. The eastern birds reach the Yukon 

 through the Rocky Mountains. Some of these, such as Chordeiles 

 virginianus^ were found only above the Tatchun River; others, as 

 Em/pidonax t. ahiorum, were absent above the Pelly and common 

 from there to Fort Yukon; others, as Wilsonia pusilla., were not 

 found above the Chandindu River; others, as Ilelniintliophila 2>ere- 

 grina were each found at a single place, while still others, as Junco 

 hyemalis and Merula viigratoria., were regularly distributed along the 

 river. The Pacific coast forms probably all reach the Yukon over 

 the Alaska coast range. These disappear as one goes north, Hylo- 

 cichla aonalasclikm extending through Lake Bennett, Wilsonia 2^- X>^^eo- 

 lata to Lake Marsh, Dendroica townsendi to Lake Lebarge, Myadestes 

 townsendi to Dawson, and Tachycineta thalassina to Circle. Last 

 and most important in number of species, abundance of individuals, 

 and regularity of distribution are birds which breed in the Yukon 

 Valley and spend the winter in the western United States, as Zono- 

 trichia I. ganibeli^ Spizella s. arizonce, and the small Ammodramus s. 

 alaudinus of the Yukon lakes, and those which probably enter by 

 the mouth of the Yukon, as the large Ammodrarmis s. alaudinus, 

 found below Alaska boundary, and Seiurus n. notabilis^ first met near 

 Dawson. 



In coloring, Yukon birds, especially in juvenile plumage, show a 

 strong tendency to replace the buff-ochraceous markings of Eastern 

 forms by white, cream color, and gray. Canachites c. osgoodi, Parim h. 

 evura, and Hylocichla u. alma are good examples of this characteristic. 



I take this opportunity to express \nj hearty thanks to Dr. Merriam 

 for the privilege of visiting Alaska as a member of the Biological Sur- 

 vey party, of writing this report, and of using the collection of the 

 Biological Survey in its preparation; also to Mr. Osgood and Mr. 

 Oberholser of the Biological Survey for aid in determining species. 

 I am also greatly indebted to Mr, Robert Ridgway and Dr. Charles 

 W. Richmond for the opportunity of studying the collection of the 



