WOOD THRUSH 107 



the young out of the nest. In Ithaca, N. Y., the nesting season ex- 

 tends from May 12 until the end of July. 



Nesting instincts are very strong in both the male and female birds. 

 The female often gives evidence of this by remaining on the nest while 

 a person walks up to it and stands within 3 feet of her. An attempt 

 was made to reach out and touch an incubating female; she sat quietly 

 until the hand was within a few inches of her before she flew. The 

 female, after banding, returned to the nest within 15 minutes, while 

 it took the male bird an hour to quiet down after being excited. 

 Several times the female returned to the nest while the male bird was 

 still uttering the quirt, quirt call of alarm. The least movement in 

 the vicinity of the nest would cause the male to utter a low trrrr 

 call. 



Eggs. — The eggs of the wood thrush are smooth, ovate in shape, 

 plain in color. According to Ridgway's "Color Standards" (1912), 

 the color is "beryl green" if the egg is dark; "pale sulphite green" 

 to "Nile blue" if it is light; or, in common parlance, greenish blue 

 much like those of the robin. The eggs of the wood thrush are smaller 

 than those of the robin and are more pointed toward the small end. 



[Author's note: The measurements of 50 eggs in the United 

 States National Museum average 25.4 by 18.6 millimeters; the eggs 

 showing the four extremes measure 28.5 by 19.3, 28.2 by 19.8, and 

 22.4 by 16.5 millimeters.l 



Authors give varying figures as to the number of eggs in a clutch, 

 varying from two to five. Data from my study show that in no case 

 was a clutch composed of five eggs. A fifth egg was laid in one case 

 after the removal of a punctured egg. Of 16 nests observed in 

 1937, the average number of eggs per nest was three. In 1938 the 

 average number in 15 nests was four. Together they average three. 



In 1938 in 15 nests, 51 eggs were laid out of which 33 young were 

 produced from which 22 survived. This is a survival of 43 percent 

 of the eggs laid, and 66 percent of the young hatched. 



Evidence at hand does not show more than two clutches of eggs 

 for any pair of birds. In one case positive evidence was obtained by 

 marking birds that the second clutch was a second brood. This 

 will be discussed later. In many cases when the first nest was broken 

 up a second nest with a second clutch was found. In one instance a 

 pair built three nests, but in the second no eggs were laid. 



An egg is laid each day until the clutch is complete. In one case 

 I observed and timed the laying of eggs and found that they were 

 laid about 10:30 o'clock on two successive mornings. 



Incubation.- — Eggs were marked so that the incubation period could 

 be determined. It was found to be 13 or 14 days. Incubation be- 

 gins with the laying of either the second or third egg. These conclu- 



