1146 U.S. NATIONAL MUSEUM BULLETIN 237 part 2 



The measurements of 50 eggs of S. a. arborea average 19.5 by 14.3 

 millimeters; the eggs showing the four extremes measure 20.8 by 15.0, 

 17.7 by 14.5, and 18.3 by 13.5 millimeters. The measurements of 

 40 eggs of S. a. ochracea average 18.8 by 14.0 millimeters; the eggs 

 showing the four extremes measure 21.8, by 15.2, 16.8 by 13.7, and 

 17.3 by 13.2 millimeters. 



In color, size, and shape, the tree sparrow eggs at Churchill displayed 

 a striking variation, not only in the different nests, but within a single 

 set. Ground color ranged from pale blue to greenish, and from a clear, 

 almost bright hue to a dull, leaden appearance. In some, the brown 

 fleckings were so evenly washed over the whole surface that the ground 

 color was almost obliterated, though generally they were more con- 

 centrated at the large end of the egg. The shape has been described 

 as oval, ovate, or ovoidal. Frequently one egg in a nest was con- 

 spicuously more rounded than the others. 



The following measurements were made during early incubation: 



Length Width 



{in milli- {in milli- Circumference Weight 



meters) meters) {in millimeters) {in gram^) 



Average 19.1 14.2 44.0 2.12 



Maximum 21.0 15.5 48.0 2.40 



Minimum 17. 5 14. 4L L 82 



Variation in one set__ 21. 14. 5 long and oval 2. 40 



(Nest VI) 19. 5 14. normal shape 2. 08 



The average egg weight equals 11.37 percent of the yearly average 

 weight of the female bird (18.62 grams). At nest I weights were 

 taken at intervals of 3 or 4 days to check the percentage of loss. Total 

 loss was 0.30 gram, or 14.63 percent. 



A normal clutch of the tree sparrow at Churchill ranged from four 

 to six eggs, the majority consisting of five. MacFarlane's (1891) 

 records for 216 nests were four to five, with occasional sets of six or 

 seven. Sets of two and three are apt to be incomplete. In order to 

 determine the capacity for laying of this species, the third egg at nest 

 II was removed each morning. Unlike the famous flicker that laid 

 71 eggs, the female settled down to incubate after her fifth egg and 

 laid no more. The experiment was not repeated, and may represent 

 only an individual case. 



Of 66 eggs in 14 nests that were watched through an undisturbed 

 hatching, five eggs or 7 percent did not hatch and presumably were 

 infertile. Of these, three belonged to a 6-egg set, and one to a be- 

 lated 4-egg set. 



After the nest was completed, the birds usually rested for several 

 days, during which they seldom visited the nest. Thereafter an egg 

 was laid daily. At five nests observed, only one bird skipped a day 



