440 U. S. NATIONAL MUSEUM BULLETIN 211 



T. C. Stephens (1917) studied the feedings of a young cowbird and 

 two young red-eyed vireos in a nest of the vireo; during a period of a 

 day and a half, the young cowbird received 58 percent of all the food ; 

 the cowbird was both older and larger than the vireos; the older vireo 

 received 27 percent of the food and the younger one only 15 percent. 



Alexander F. Skutch writes to me: "On May 20, 1931, 1 found under 

 a bridge near Ithaca, N. Y., a phoebe's nest containing four of its 

 own eggs and one newly hatched cowbird, half of its shell still remain- 

 ing in the nest. On May 22, there were two young phoebes, hatched 

 since the preceding day. The cowbird appeared to be fully four or 

 five times their size. Its eyes were partly open and the sheaths of 

 its remiges were sprouting. By May 25, one phoebe nestling and 

 one of the unhatched phoebe eggs had mysteriously vanished. By 

 May 28, the cowbird was well feathered, could perch, and showed 

 fear. The young phoebe, six days old, was still blind and was very 

 weak and helpless; its pin feathers were just sprouting. Ob May 29, 

 I found the cowbird on the rim of the nest. The young phoebe's 

 eyes were just opening. By May 30, the cowbird had left the nest, 

 aged ten days. By June 3, the phoebe was well feathered. By 

 June 6, the young phoebe had departed, at the age of fifteen days. 

 The parent phoebes were feeding the young cowbird nearby, and 

 the female had already laid a new egg in the nest! Returning on 

 June 12, I found her incubating five eggs of the second brood in the 

 old nest. 



"On July 29, also near Ithaca, I found a nest of the red-eyed vireo 

 with two young vireos and one cowbird, all about a week old. By 

 August 2, the cowbird had left the nest; the vireos, still inside, were 

 in a thriving condition and seemed about ready to depart." 



Friedmann (1929) made a careful study of the growth and develop- 

 ment of the young cowbird in the nest; it is not essentially different in 

 pattern from the development of other young passerine birds, except 

 lor its increase in weight — the really important factor in its survival: 

 "This Cowbird, probably less than an horn- old, weighed 2.5 grams. 

 * * * The average weight of a day old Cowbird is 4.5 grams. * * * 

 At the end of the second da} r the young Cowbird may weigh from 

 7.5 to 8.5 grams. * * * For the first two days, the daily increase is 

 close to 100 per cent, but from then on the rate is slower, averaging 

 about 50 per cent on the third day and gradually lessening until it 

 comes to be about 10 per cent on the eighth day and only 5.5 per cent 

 on the ninth. When the Cowbird leaves the nest it averages about 

 33 grams or approximately 13 times its weight on hatching." 



The rate of growth varies considerably, depending largely on the 

 kind and amount of food furnished by different species of foster parents. 



