86 U.S. NATIONAL MUSEUM BULLETIN 2 65 



me to think the eggs may be laid at intervals of one day. More direct, 

 observational data are supplied by Pringle (Ostrich, 1946, pp. 368- 

 369) who noted a female didric (ostensibly, but not absolutel}^ cer- 

 tainly, the same individual) returning to a Cape sparrow's nest on 

 three successive days, and each day depositing an egg in the nest." 



Recently Ottow and Duve (1965, p. 433) have interpreted Duve's 

 very intensive and important field observations to imply a much 

 longer interval between eggs — at least four days. This surprising con- 

 clusion was based on Duve's conviction from his observations that 

 he was reasonably certain that only three or four female didrics were 

 in attendance as parasites on a colony of red bishops, Euplectes orix, 

 and that he had practically every nest under observation. From this 

 he assumed that, if, as he thought, these didrics parasitized only the 

 bishops (and they would have had to fly "considerable distances" to 

 lay in other nests of other colonies of the same host) and if they laid 

 at daily intervals, he would have expected at least three or four times 

 as many didric eggs as he found in his daily inspection of each nest 

 in the colony. 



The weak points in Duve's data are that his cuckoos were not 

 marked for easy individual sight identification, that he may have 

 faUed to find some of the bishops' nests, and that the cuckoos might 

 have made "considerable flights" to other host colonies or might have 

 laid some of their eggs in nearby nests of other species of birds. In 

 other words, the four day interval postulated is an interpretation and 

 not an established fact. At the same time, it should be stressed that 

 while Duve's conclusions are at variance with Pringle's observations 

 and with the results of an examination of the ovarian follicles, the 

 intensity and meticulousness of Duve's field work make his work 

 worthy of serious consideration. It is to be hoped that further studies 

 along the same line may be made for the additional light they may 

 shed on this problem. In our present state of knowledge, I do not 

 think it hkely that a four-day interval exists, but at the same time I 

 would not rule out, or ignore, Ottow and Duve's interpretation. 

 Further substantiation in greater detail is needed to make it acceptable 

 because of the exceptional and unexpected length of this longer 

 interval. 



Duve (both in litt. and in his joint paper with Ottow [1965]) has 

 attempted to coordinate a longer egg interval with the fledgling- 

 feeding tendency of the adult didric. This I think is unnecessary, 

 since the feeding of newly fledged didrics by adults of their own 

 species is apparently an occasional rather than a "routine" behavior 

 and as far as published observations indicate, is done mainly by the 

 males and not by the egg-producing females. 



