1520 U.S. NATIONAL MUSEUM BULLETIN 237 part 3 



D. J. Nicholson found no cowbird eggs or young in any nests during 

 9 years of observation in North Carolina. But in July, 1954, he saw a 

 fledging cowbird being fed by a Mississippi song sparrow. "Appar- 

 ently cowbirds are extremely scarce in that region of North Carolina 

 and have just come there," he wrote. 



Turning to egg and nestling losses from all causes, 44 percent of the 

 eggs laid left the nest as fledged young during the first 2 years of the 

 Interpont study and 29 percent during the next 4 years; 36 percent of 

 the eggs yielded fledglings during the 6 years. The first 2 years, during 

 which conditions for reproduction were favorable, correspond well 

 with results of other studies on altricial young in open nests. The 

 poor success afterwards reflected the disturbed conditions of the 

 environment. The percentage losses suffered by eggs and nestlings 

 of 906 eggs laid during 7 years was: flood 2.8 percent, predators 36.7 

 percent, cowbird 6.1 percent, sterile and addled eggs 5.6 percent, 

 parental failure 2.4 percent, man 4 percent, parents killed 3.7 percent, 

 young starved 3.1 percent. For all eggs laid these figures represent a 

 death of 40.9 percent in the egg stage, and of 23.5 percent after the 

 nestling stage was reached — 64.4 percent in all. 



The survival of the adult breeding males averaged over 60 percent 

 during the first 2 years, but after that dropped to 48, 23, 30, and 20 

 percent. The loss of breeding males from April to June averaged 15 

 percent during the first 3 years, 30 percent during the next 3 ; the loss 

 of breeding females averaged 30 percent and 35 percent during the 

 same periods. The proportion of first year males in the population 

 ranged from about 26 to 55 percent. 



Out of 317 fledged nestlings 26 males and 14 females were later 

 found as breeders. The late arrival of young females doubtless raises 

 difficulties in the way of return to the vicinity of the birth place. 

 The percentage of yearly return of birds, without regard to sex, ranged 

 from 4.5 to 20, averaging 12.6; and 4.5 percent of the eggs laid produced 

 birds that returned to breed on the area. If the population is to be 

 maintained it is estimated that an average of 20 percent of the fledged 

 young should survive to adulthood. It is believed that 50 to 60 

 percent of the young song sparrows that survived to breed returned 

 to the place of birth to do so. 



In a well-situated group of song sparrows the average life of the 

 breeding males was 2^ to 2% years. Individuals have been known 

 to have reached 7 years of age, while one male was at least IY2, and 

 perhaps 9}4 years old at his death. 



Fall. — There was always singing in the fall from the males on their 

 territories, much in mild weather, little in bleak. Usually the summer 

 residents sang for only a few days the last of September and first of 

 October, but some residents might sing well into November. In 



