TREE SPARROW 1147 



(between the second and third eggs). The eggs were hiid in the early 

 morning, between G:00 and 7:30 a.m. At nest I the second egg had 

 not been deposited at 6:45, but was laid before I returned at 7:45. 

 On the 4th day the new egg was in the nest when I arrived at G:30. 



During egg laying the birds show somewhat more interest in the nest. 

 In 10 visits to nest I during this time, I found the female covering the 

 eggs on two occasions, once from 5:30 to 6:00 a.m., returning at 6:25 

 to lay, and once in mid-afternoon. In addition the male visited her 

 twice, and came once when she was absent. Other females were found 

 on their nests at various hours of the day. When nest B contained 

 one egg, the bird was flushed at noon, returning in about 15 minutes 

 with a bill fuU of grasses. It is believed that the females roosted there 

 at tliis time, as nest II A\dth foiu" eggs was occupied at 10:15 p.m., and 

 another with one egg at 5:30 a.m. 



Incubation is performed by the female only, and begins normally with 

 the la3dng of the last egg. At nests III and IX another egg was laid 

 after incubation had apparently commenced. It may be significant 

 that at both nests one egg hatched much later than the others, and this 

 last young died before its first day was over. 



During the first days, the female at nest I was absent for long periods, 

 and on the morning of June 18, 2 days after the set had been completed, 

 the eggs felt ominously cold. Twenty minutes later I found her 

 incubating persistently, and thereafter she was seldom long absent. 

 About two-thirds of the working day she spent on duty, a ratio she 

 maintained throughout the period. While the percentage of time did 

 not vary appreciably, it was noted that during late incubation the 

 periods on and off the nest were of much shorter duration. These 

 facts are indicated by the following figures, compiled from 3- and 2- 

 hour observations, respectiveh^, at mid- and late incubation. Ir- 

 rationally, the longest period away from the nest occurred during a 

 brief cold shower. 



6 days of 11 days of 



incubation incubation 



Time on nest 61.80 percent 61.78 percent 



Time off nest 38.20 percent 38.22 percent 



Average length of period on nest 21.6 minutes 7.6 minutes 



(max. 31) (max. 34) 



Average length of period off nest 1 4.0 minutes 5.2 minutes 



(max. 33) (max. 12) 



The incubating female crouches low in the nest Mith neck dra^n in, 

 wings laid compactly against the back, and tips of primaries crossed 

 over the rump, only the bill and tail extending beyond the rim of the 

 nest. This position is conspicuously different from the brooding 

 posture, when she sits high over the nest, frequently panting from 

 heat, neck outstretched, ^vings drooping over the rim of the nest. 



