1152 U.S. NATIONAL MUSEUM BULLETIN 237 part 2 



of this is due to fading, as Dwight intimates, but the chief change is 

 by actual wearing away of the feather edges. 



During the spring there is in addition a restricted molt of which 

 Dwight (1900) says: "New feathers regularly grow on the chin in 

 March, but apparently not in the other tracts and their appearance 

 indicates, as in some other species, renewal rather than molt, for 

 they are very few in number." It was found, however, to be more 

 extensive, for of 130 specimens examined, fresh sheaths were evident 

 regularly on cheeks and chin, later on the throat, and other tracts 

 were affected in the following proportions (in this count scattered 

 feathers were not considered, but only definite areas of new quills): 



Number of 

 Specimens 

 Showing 

 Tract Molt 



Crown (sides and back only) 5 



Superciliary stripe 6 



Lores 3 



Nape 10 



Dorsal tract 19 



Scapulars 4 



Rump 2 



Sides 5 



Belly 6 



Adult winter plumage is "acquired by a complete postnuptial molt, 

 undistinguishable from fii'st winter dress" (Dwight, 1900). At 

 Churchill the first evidences of this plumage were detected on 

 July 31, 1933, and on Aug. 3, 1934. Sequence was in-egular, but in 

 general contour feathers preceded the flight feathers, and the molt 

 progressed from the anal region toward the head. 



Although tree sparrows are described as "sexes identical," a de- 

 termined effort disclosed minor differences in plumage and measure- 

 ments, a combination of which may distinguish up to 90 percent of 

 birds at banding stations (Heydweiller, 1936). Using specimens which 

 were later dissected to determine sex (by gonads) and age (by skull), 

 a practical test with 129 birds gave the following score: 



Male adult 36 birds, all judged correctly 



Male immature 43 birds, 5 incorrect 



Female adult 19 birds, 7 incorrect 



Female immature 31 birds, all judged correctly 



Percentage of error 9.3 (due to overlap of characteristics 



of young males and adult females) 



Criteria used in distinguishing sex and age are primarily lengths of 

 wing and tail, width of crown, and amount of veiling of the crown. 

 In general the largest birds are adult males, the smallest ones with 



I 



