EASTERN HERMIT THRUSH 147 



NEST FOUND AT BRUNSWICK, MAINE, JULY 16, 1928 



The measurements of 40 eggs in the United States National Museum 

 average 22.1 by 16.8 millimeters; the eggs showing the four extremes 

 measure 23.6 by 17.3, 22.6 by 18.0, 20.1 by 17.5, and 20.8 by 15.8 

 millimeters. 



Incubation. — The determination of the incubation period of 12 days 

 is based on the study of two nests that were under continuous daily 

 observation at Brunswick, Maine. On May 26, 1928, a nest of the 

 hermit thrush located at the base of a small fir tree contained two eggs. 

 On May 27 there were three, and on May 28 the set of four eggs was 

 completed. Incubation, however, did not start until the following 

 day, May 29. At 8 o'clock on the morning of June 10 there were 

 three freshly hatched young, and the fourth hatched during the 

 afternoon. A second nest was nearly completed but contained no 

 eggs when it was found on June 10, 1940. This nest was in a natural 

 depression located in a thick growth of blueberry vines. The first 

 egg was laid during the morning of June 12. On June 16 there 

 were four eggs and incubation started. The first egg laid hatched 

 at 5 p. m. on June 28; the other three were hatched by dawn the next 

 morning. The incubation period of the hermit thrush as reported by 

 various observers varies from 10 to 13 days, but this wide range does 

 not represent a real variation but probably is due to the failure to 

 ascertain the exact time of the beginning of incubation as well as that 

 of hatching. 



In the nests I have had under observation only one of the pair, 

 presumably the female, took part in the incubation of the eggs. The 

 incubating bird was seen to leave the nest in search of food, but much 

 of the food was delivered to her by her mate while she was attending 

 her duties on the nest. During the 12 days of incubation the male 

 spent much of his time singing and serving as guard against the in- 

 trusion by other birds or enemies that appeared in his territory. He 

 often chose as a sentinel post the lower branch of a large pine tree 

 that stood about 40 feet Jroni the nesting site. At other times he 



