EASTERN BROWN-HEADED COWBIBD 437 



that "a little hen Cowbird that had the liberty at all times in a suite 

 of rooms, was tempted by me to enjoy as nearly as possible its natural 

 bent in the direction of egg laying and the results obtained in the way 

 of information were somewhat surprising. Eight or ten last year's 

 nests were placed around the room, with dummy (candy) eggs in 

 them; each morning about six o'clock the little hen would seek some 

 nest or other in which it would drop her egg, but not always in the 

 same nest; often times, the candy egg would be found on the floor; so, 

 in fourteen successive days, the little hen had laid thirteen eggs; this 

 would indicate apparently that the destructive nature of the bird is 

 even greater than it has been thought to be." 



Lawrence H. Walkinshaw (1949) concluded during his studies in 

 Michigan, that 25 eggs were laid between May 15 and July 20, 1944, 

 by a single cowbird "because (1) they were very similar in coloration 

 (2) no two were laid on the same day (3) the length of 11 similarly 

 colored eggs had significantly less variability than the length of 22 

 not-similarly colored eggs." 



As to the number of eggs laid in any one nest, we have plenty of 

 positive information; Friedmann (1929) writes on this subject: 



In order to determine definitely whether or not the Cowbird normally lays 

 but a single egg in a nest, data on approximately nine thousand victimized nests 

 of one hundred and ninety-five kinds of birds were assembled, and it was found 

 that in over two-thirds of the cases only one parasitic egg was found in a nest. 

 This shows pretty clearly that the normal, the usual, the characteristic thing is 

 for a Cowbird to deposit one egg in a nest. 



Nevertheless about a third of the nests held more than a single Cowbird's 

 egg apiece. This is no inconsiderable number or percentage of exceptions to the 

 above rule, and calls for an explanation. It has been shown that under normal 

 conditions each pair of Cowbirds has a more or less definite territory and that 

 the female tends to restrict herself to nests within that particular area. However, 

 the cyclical instincts of the female are so aborted that she is probably quite 

 easily induced temporarily to forsake her territory long enough to deposit an 

 egg in a near-by nest. * * * Again, in regions where the Cowbird is very common 

 (and this applies to a great part of its range) territories are apt to overlap and in 

 this way two Cowbirds may make use of the same nest. In this way I believe 

 we can account for the fact that not infrequently eggs of two or more rarely even 

 three different individuals are found in the same nest." 



Furthermore, a cowbird may lay more than one of her own eggs in a 

 nest, provided she can find at the proper time no nest in which she 

 has not already laid. 



Mrs. Nice (1939) says: "During seven years' study on Interpont, 

 98 of the 223 Song Sparrow nests located contained Cowbird eggs; 

 69 held one egg, 26 held two eggs and three held three. Only once 

 did I find four Cowbird eggs unla ^single nest; this happened in June, 

 1928, and the nest belonged to a Maryland Yellowthroat." (See, 

 also, her (1949) paper on the laying rhythm.) 



