EASTERN BROWN-HEADED COWBIRD 435 



herself slightly but remained a few seconds before flying away. Upon examining 

 the nest I found a fresh Cowbird egg. Undoubtedly the egg was being laid as the 

 picture was taken. 



He ends the story with the statement that: "Two sparrows and the 

 Cowbird hatched and were reared successfully until the Cowbird was 

 seven, the sparrows six days old, when the nest was destroyed by a 

 predator." 



Harry W. Hann (1941), in the studies of the cowbird at the nest 

 of the oven-bird, came to the following conclusions: 



1. The female Cowbird regularly finds the nest of the host by seeing the birds 

 building. 



2. She sometimes watches the building process intently and this doubtless 

 stimulates the development of eggs, which are laid four or five days later. This 

 theory, first suggested by Chance for the Cuckoo, accounts for the delicate syn- 

 chronization of the egg-laying of the Cowbird with that of the host, and does not 

 preclude the possibility of laying several eggs^on successive days. 



3. The eggs of the Cowbird are usually laid during the egg-laying time of the 

 host, but exceptions are common. Extremes noted during the study were three 

 days before the first Oven-bird's egg was laid, and three days after incubation 

 began. 



4. A Cowbird lays but one egg in a nest unless nests are scarce; in that case it 

 lays more. 



5. The female Cowbird makes regular trips of inspection to nests during the 

 absence of the owners, between the times of discovery and laying, and knows in 

 advance where she is going to lay. 



6. Her regular time for laying is early in the morning before the host lays, and 

 she will frighten the owner from the nest if she happens to be there first. * * * 



7. The Cowbird is both alert and determined when she come to the nest to lay. 

 She moves about in the vicinity of the nest and looks carefully for as much as 

 three minutes before entering, but will return to the nest if she is frightened away. 



8. She spends from a few seconds to a minute in the nest when laying and flies 

 directly from the nest as soon as the egg is laid. 



9. The Cowbird disturbs the nest of the Oven-bird but little when she enters to 

 lay, and I have found no broken eggs which were attributable to her entering. 



10. Parasitized nests regularly have one or more eggs removed by the female 

 Cowbird. These are not removed at the time of laying, but during the forenoon 

 of the previous day, or the day of laying, or rarely on the following day. * * * 



11. Eggs removed are eaten by the Cowbird, but are not removed for that pur- 

 pose along, or their disappearance would not be correlated so closely with the lay- 

 ing of her own eggs. The number of eggs removed from parasitized Oven-birds' 

 nests was eighty-five per cent of the number of eggs laid [by the cowbird] and in- 

 cluded four eggs of the Cowbird itself. From nonparasitized nests of the Oven- 

 bird only a single egg disappeared during the study. 



12. The statement by Borroughs that a Cowbird takes an egg from a nest only 

 when two or more eggs are present is borne out by this investigation. 



Mrs. Nice (1939) has twice seen a cowbird remove an egg from a 

 song sparrow's nest, "the thief eating the egg and shell," in one case. 

 And T. S. Roberts (1932) has seen one remove an egg from a scarlet 

 tanager's nest and from the nest of a chipping sparrow. W. V. 

 Crich, of Toronto, has sent me a photograph of a cowbird 's egg in a 



