434 U. S. NATIONAL MUSEUM BULLETIN 211 



performer. Two-story nests of this warbler are fairly common, where 

 cowbirds are numerous, * * * three-storied nests are not very rare, and as 

 many as four or even five stories have been built. In addition to those 

 birds mentioned above as addicted to this habit, R. M. Anderson 

 (1907) reports a "Traill Flycatcher's nest with a Cowbird's egg 

 imbedded." C. R. Keyes (1884) found a scarlet tanager's "nest with 

 a Cowbird's egg embedded in the bottom." Amos W. Butler (1898) 

 reports a nest of the Maryland yellowthroat, containing three stories. 

 "Two additional nests were built upon the original structure, buiying 

 beneath each the egg of a Cowbird." E. A. Samuels (1883) claimed to 

 have a double nest of the American goldfinch in his collection, but 

 this seems open to question, as the goldfinch usually nests later in the 

 season than the cowbird. 



The female cowbird is an expert nest hunter; in fact, she has to be. 

 Coues (1874) describes her nest hunting graphically: 



It is interesting to observe the female Cow-bird ready to lay. She becomes 

 disquieted; she betrays unwonted excitement, and ceases her busy search for 

 food with her companions. At length she separates from the flock, and sallies 

 forth to reconnoitre, anxiously indeed, for her case is urgent, and she has no home. 

 How obtrusive is the sad analogy! She flies to some thicket, or hedge-row, or 

 other common resort of birds, where, something teaches her — perhaps experience — 

 nests will be found. Stealthily and in perfect silence she flits along, peering fur- 

 tively, alternately elated or dejected, into the depths of the foliage. She espies 

 a nest, but the owner's head peeps over the brim, and she must pass on. Now, 

 however, comes her chance; there is the very nest she wishes, and no one at home. 

 She disappears for a few minutes, and it is almost another bird that comes out of 

 the bush. Her business done, and trouble over, she chuckles her self-gratulations, 

 rustles her plumage to adjust it trimly, and flies back to her associates. 



Russell T. Norris (1944) gives the following account of a cowbird 

 laying in a song sparrow's nest, which was photographed by Hal H. 

 Harrison (see pi. 25) : 



Just before 4:30 a.m., about 22 minutes before sunrise, we heard the sputtering 

 note of a Cowbird, and a few seconds later a female Cowbird alighted on the 

 camera. After looking around cautiously, she flew to the ground at the base of 

 the tripod and began to walk nervously toward the nest. As she reached the rim 

 of the nest, she paused and carefully surveyed the surrounding territory, then 

 stepped into the nest, and turned about several times. Finally she settled down, 

 and Harrison pressed the button on the battery. As the flash went off, the Cow- 

 bird flushed. She had been on the nest no more than 15 seconds and had not 

 deposited her egg. * * * 



At 4:38 a.m. I noticed a movement in the grass behind the nest, and after a 

 few seconds the Cowbird appeared. She approached the nest warily, stepped up 

 onto the rim, and paused there. Then she entered the nest and began to turn 

 about as she had on her previous visit. After a few seconds, she stepped back 

 onto the rim and looked around. She three times repeated this procedure of 

 standing on the rim, then uneasily turning about in the nest. In one instance she 

 mounted the rear rim and looked back into the grass. At approximately 4:40 a.m. 

 she settled on the nest, and Harrison released the shutter. The Cowbird raised 



