1224 U.S. NATIONAL MUSEUM BULLETIN 23 7 part 2 



"russet," or "hazel." Undermarkings are "light mouse gray," but 

 these are often absent. The eggs are somewhat delicately marked, 

 and the spots may be either sharply defined or clouded. The markings 

 tend to be concentrated toward the large end, where they may form 

 a loose wreath, but they are often scattered over the entire surface. 

 The measurements of 58 eggs average 17.6 by 13.1 millimeters; the 

 eggs showing the four extremes measure 19.8 by 14.0, 17.8 by 14-8, 

 15.8 by 12.5, and 17.3 by 11.9 millimeters. 



A total of 446 clutches in my Michigan study area varied from two 

 to five eggs with an average of 3.37 eggs per set; early nests contained 

 more eggs, later ones fewer, as the following table shows: 



The measurements of 1,308 eggs averaged 17.9 (16.1-21.0) by 13.5 

 (12.3-14.7) millimeters. Their average weight was 1.73 (1.35-2.1) 

 grams. As described above, the eggs vary considerably in color, and 

 those laid by each female were often so distinctive I was confident 

 which female laid them in many nests I found, even before I had 

 positively identified her. Eggs in the same set were often similar in 

 size, and I found no discernible trend in measurements and weights 

 of eggs as laid in the set; some first eggs were smaller, some larger 

 than those laid later. 



Almost invariably one egg is laid per day imtil the set is completed. 

 Eggs were laid early in the morning, some before 5:00 a.m., but the 

 majority between 5:00 and 6:30 a.m. Occasionally the last egg of a 

 clutch was laid slightly later, even after 8:00 a.m. 



Incubation is entirely by the female, but on rare occasions a male 

 may be found on the nest. One male I watched spent the entire 

 night over young that had just hatched when the female was afraid 

 of the trap I had placed over the nest. But if a female was killed, 

 rarely did the male continue the nesting activities until he acquired 

 a new mate. One male fed the small young but did not brood them, 

 and they soon died. 



Though the female may be found on the nest almost any time after 

 the first egg is laid, she usually does not start incubating steadily 

 vmtil the night before she lays the last egg. Crooks (MS.) found that 

 females incubated 70 percent of the daylight hoiu"s and were off the 

 nest only 30 percent. While the female incubates the male sings near 

 by, stopping occasionally to feed. At times he brings food to the 



