436 U. S. NATIONAL MUSEUM BULLETIN 211 



last year's nest, showing that this clever nest hunter sometimes makes 

 a mistake. 



Eggs. — To determine the number of eggs laid by the cowbird 

 during a season is a question that cannot be answered with certainty, 

 but we have some data indicating that it lays no more eggs than 

 many other passerine birds. Friedmann (1929) made a careful and 

 thorough study of three well-known cowbird territories, in which all, 

 or nearly all of the nests were located and in which the eggs of the three 

 different females could be recognized. Of these he says: 



Two of the birds laid five eggs each and the other laid four. In one of the cases 

 where five eggs were laid (Terr. A.), I found no more after the fifth one although 

 a great deal of time was spent in this breeding area. It was just because no egg 

 was found on the sixth day that I kept very close watch of the bird and its terri- 

 tory on that and the following day. On the day this individual laid its fifth egg 

 the other "five-egg" bird, (B), laid its first. For four days thereafter this bird 

 (B) laid an egg daily and no more were found for individual A. On the day 

 Cowbird B laid its fifth egg a heavy storm broke out and for a month and a half 

 thereafter it rained more or less violently every day. As fast as nests were found, 

 they were destroyed or washed away by the heavy rains, and, of course, it became 

 impossible to keep any check on the actions of the Cowbirds. * * * 



Above it was stated that no eggs were found in the territory of Cowbird A after 

 that bird had laid its fifth. Of course the mere fact that none were found is no 

 indication that none were laid. However, the second of the "five-egg" birds 

 (individual B), was collected three days after it had laid its fifth egg. Only five 

 discharged egg follicles were found in its ovaries and the oldest of these follicles 

 was still very prominent so that if any more eggs had been laid, follicles would 

 have betrayed the fact. This shows pretty conclusively that only five eggs were 

 laid in the case of this bird. This, together with the fact that bird A was known 

 to lay at least five eggs and, judging by the four-day rest (?) after the laying of 

 the fifth egg, probably did not lay any more, suggests the idea that five eggs may 

 possibly represent what in other birds would be called a clutch "'although this is 

 doubtful. We cannot be certain that Cowbird A laid only five eggs although I 

 feel that I would have found at least one more egg in the four days between the 

 fifth egg and the stormy season, if the bird had kept on laying. * * * 



A record of the eggs laid by each bird and the nests used may be of some inter- 

 est. Cowbird A laid its first egg on May 23 in the nest of a Chestnut-sided War- 

 bler; its second egg, May 24, in a Veery's nest, its third, May 25, in another 

 Veery's nest, its fourth, May 26, in a nest of a Redstart, and its fifth, May 27, 

 in the same Redstart's nest. 



Cowbird B laid its first egg May 27 in a nest of Redstart, its second egg May 28, 

 in the same nest, its third, fourth, and fifth, on May 29, 30, 31 respectively, all 

 in one nest of a Red-eyed Vireo. 



Cowbird C laid its first egg May 22 in a Veery's nest, its second, May 23, in a 

 nest of a Redstart, its third, May 24, in the same nest, and its fourth and last 

 recorded egg, May 25, in a Red-eyed Vireo's nest. 



From the above it may be seen that the cowbird lays one egg each 

 day, and that it is not specific in its choice of hosts. As evidence that 

 the cowbird may sometimes lay more than five eggs, Friedmann 

 quotes F. L. Rand, who had kept cowbirds in captivity, as saying 



