The Oologists' Record, March 1, 1923. 19 



COWBIRD [Molothrus ater ater) LAYS EGGS DIRECT 

 FROM OVIDUCT INTO THE NEST OF ITS VICTIM. 



By J. Warren Jacobs, Director, Museum of Applied Oology, 

 Wayneshurg, Pa. 



I will not stake a wager on the statement that the Cowbird 

 always lays its eggs direct from the oviduct into the nest of its 

 victim ; but my experience with the egg deposition of this bird 

 leads me into the firm belief that this is their accustomed way — 

 possibly their only way ! 



In the first place, the hiuidreds of nests or other lairds in which 

 I have found eggs of the Cowbird, were all of a character of easy 

 access to the parasitic species. Exceptional cases, however, were 

 nests of the Tufted Titmouse, Bluebird and White-bellied Nuthatch, 

 but with each of these the Cowbird could have entered for laying 

 its eggs more easily by expulsion from the oviduct than by carrying 

 in the beak. 



In the second place, the short, narrow, hard and straight bill 

 of the Cowbird is not capable of retaining an uncrushed egg while 

 the bird's body undergoes the physical exertion necessary to enter 

 some nests. 



I have found several nests of Bluebird in which the Cowbird 

 had laid eggs, but I could insert my hand in anj^ of the openings, 

 and the nests were, as a rule, on a level with the entrance. Once 

 an egg was found in a nest of the White-breasted Nuthatch, in a 

 natural knothole in an oak tree, but this nest was level with the 

 entrance, and the entrance itself, was large enough to admit the 

 Cowbird. 



The most remarkable case is that of a nest of a Tufted Titmouse, 

 found May 7th, 1887, 18 inches deep, in which was a Cowbird's 

 egg with those of the rightful owner ; but in this case, the cavity 

 was straight down in the top of a small oak stub, and I had no 

 difficulty in inserting my arm. 



My experience with this bird in open nests, where it was actually 

 seen and watched, is briefly stated in the following cases : — 



Scarlet Tanager, Phoebe, Yellow-breasted Chat, Louisiana 

 Water-Thrush and Kentucky Warbler : actually flushed Cowbirds 

 from all these nests. 



Worm-eating Warbler : after removing nest and eggs of this. 



