1140 U.S. NATIONAL MUSEUM BULLETIN 237 part 2 



with a pronounced crest the 4th week. Smaller crests occurred 

 in mid-April for migrants, while the number of winter residents 

 decreased steadily through the month. Interestingly, the last 

 birds to leave on May 1 were on of my winter "standbys" and a winter 

 resident from the Frazer station. 



The proportion of the sexes during spring migration indicates that 

 these birds do not travel as mated pairs. In late February at the 

 end of the winter period, males constituted 90 percent of the birds 

 collected from a flock near Ithaca. Thereafter the percentage of 

 females increased steadily until it equaled the males in late March, the 

 crest period for departing winter residents and incoming migrants. 

 During the mid-April crest, proportions were nearly equal again 

 with 45 percent male birds, many of which upon dissection showed 

 evidence of immaturity. On April 26 the last collection netted 86 

 percent females and a sprinkling of small males, presumably first year 

 birds (Heydweiller, 1936). 



Nesting. — At the beginning of my graduate study on the life 

 history of the tree sparrow, I wrote hopefully to Mr. Bent for any 

 available information on the nesting habits of this species. He 

 repUed that there was little beyond locaUty records and descriptions 

 of nests and eggs, adding tersely, "It is regrettable that you did not 

 select a bird you could study in the field yourself." The following 

 account is the outcome of that brief comment (Baumgartner, 1937b) : 



In the wet, brushy wastes of the Canadian Northland, beyond 

 arable land or usable timber, from the northern thhd of the Hudsonian 

 spruce timber as far north as there is any scrubby growth, the tree 

 sparrows find optimum conditions for nesting and for rearing their 

 young. Churchill, Manitoba, at latitude 58" N. haKway up the west 

 coast of Hudson Bay and 5 miles beyond timberhne, proved an 

 ideal locality to study the nesting habits of this species. Connected 

 by rail mth the outside world in 1929, it was then the only spot that 

 could be reached early enough in the season to trace the complete 

 nesting cycle without spending a winter in the North. The embryo 

 town was hospitable, and the nearby river flat, a bouldery, hummocky, 

 pool-dotted stretch of tundra extending back to timberline, was 

 interspersed with patches of scrub birch and willow, a maximum of 

 4 or 5 feet high, in which tree sparrows were one of the most 

 abundant species. 



During 5 months spent on the nesting grounds — throughout June 

 and July in 1933 and from June 4 to August 21 in 1934 — I found a 

 total of 26 nests, 9 of which were kept under constant observa- 

 tion from the time of their discovery. While the birds were common, 

 their nests, usually hidden in the densest tangles of the scrubby 

 thickets, were difficult to find. The nests studied, however, showed 



