1172 U.S. NATIONAL MUSEUM BULLETIN 23 7 part 2 



Street (1954) reports on 63 clutches in the vicinity of La Anna in the 

 Pocono Mountains of northeastern Pennsylvania and Walkinshaw 

 (1944b) reports on 45 complete clutches in southern Michigan as: 



No. of sets (Street) 



No. of sets (Walkinshaw") . 



Walkinshaw found that the average clutch size decreased from 3. 81 

 in May to 3.00 in July. 



Sets containing five eggs have been reported from Newton, Mass. 

 (G. M. Allen, 1892), Buckeye Lake, Ohio (Trautman, 1940), St. Louis 

 County, Minn. (Roberts, 1936), and Flotten Lake, Saskatchewan 

 (Robert P. Allen, ^c/e Godfrey, 1950). 



Some variation in egg color and marking has been found. Over a 

 5-year period Walkinshaw (1952) examined 35 eggs from the same 

 female and found them aU darker blue than the usual chipping spar- 

 row eggs, and the markings, usually sparse scrawls, were heavy black. 

 A clutch of unspotted eggs has been reported (Oologist, 1884:70). 



Incubation. — Incubation begins on the day before the last egg is laid. 

 Usually the female does all the incubating, but Walkinshaw (1944b) 

 reports one instance of the male incubating. 



Walkinshaw (1952) determined the incubation period for nine 

 nests and found a relationship between the au- temperature and the 

 length of the incubation period. The four nests that were incubated 

 during the period of highest average mean temperature (66.2° to 

 76.0° F.) had 11-day incubation periods, while when the average mean 

 temperature was lowest (48.7°) the incubation period was 14 days. 



As with many song birds, the male feeds the female while she in- 

 cubates. As he approaches the nest tree he utters a series of low 

 chips, sometimes rapidly. At the sound the female becomes alert 

 and restless, and sometimes leaves the nest to feed near by. At 

 other times she remains on the nest. In one case the male came to the 

 nest and fed the female only 3 minutes after she returned to the nest 

 from being with him. She often chips rapidly, flutters her wings, 

 and begs as he arrives. 



The incubating female often can be approached quite closely, which 

 I found most convenient. I marked a number of females on the nest 

 for identification by applying model airplane dope to them with the 

 tip of a stalk of timothy grass. 



Young. — When the eggs hatch the female eats the shell (Walkinshaw, 

 1944b). The young, which are capable of only one activity, feeble 

 gaping, are fed almost immediately. Walkinshaw (1944b) watched 

 a female feed one young 20 minutes and another 28 minutes after 

 hatching. I have observed two fu-st feedings. In one case the male 



