166 



PACIFIC COAST AVIFAUNA 



No. 14 



it is the eommont'st species i'oiind on the sliores of Flathead Laki'. lii'eeds in the 

 Tj-ansition and Canadian zones, in coniferous forests oi' in forests of conifers 

 and hi-oaddeaf trees mixed. Occurs in migration in the eastern part of the state, 

 where^ it is regular hut not connnon. The easternmost records of its hreeding 

 are from the Belt ilountains (Willianis, 1890b, p. 292), the mountains of Fergus 

 County (Silloway, 19(K5a, p. 69), and the Big Horn iMountains (McChesney, 

 1879, p. 2384). \ 



The migrations take place in May and September. Dates of spring migra- 

 tion in i)ortions of the state where it does not breed are as follows: Custer Coun- 

 ty, May ;3], 1906 (Cameron, 1908a, p. 55) ; Miles City and vicinity, May U to 

 June 7, 1902, thirteen specimens (Hedges, coll. Univ. JNIontana). In regions 

 where this species breeds it arrives about the middle of ^lay. Three years at 



Fig. 34. NiosT AND EGGS OF THE Olive-backed Thhusii. Yellow Bay, 

 Flathead Lake; June 29, 1914. 



Great Falls, give an average of Uny 15, and llie earliest May 3, 1892; three years 

 at Columbia Falls average .May 19, the earliest May 17, 1896 (Cooke, 1907, p. 

 122). In the Belt IMountains it is said to arrive IMay 10 (Williams, 18901), p. 

 292). Other dates are : l^ozeman, June 1, 1909 ; Norton Gulch, Silvei- Bow Comi- 

 ty, May 16, 1910; Anaconda, Mny 14, 1911 ; (^hoteau. May 22, 1912; Teton River, 

 May 28, 1915; and Dutton, May 27-June 4,' 1916 (l)uBois, MS). Fall migration 

 takes [)lace from September 1 to Octo])er 10 (Williams. 1S!)01), p, 294). The lat- 

 est (late at Columbia Falls is September 23, 1895 (Cooke, 1907, p. 124). The 

 only other definite fall date 1 kuow of is from Sun River, Se])tvmber 4, 1912. 



Nesting begins about the iiii<ldle of •luue, and eggs may he loniid from then 

 until the middle of .July. The earliest date for a coiuplete set oi' eggs is 4 (me 

 17, 1900 (Silloway, l!)01a, p. 10), and the latest is July 19, 1902 (Silioway. 



