NO. 3 THE PROBLEM OF THE VIDUINAE — FRIEDMANN 7 



zations of the various host species of the genus Estrilda, as de- 

 scribed in the literature, are all quite similar, or at least their 

 specific patterns vary only slightly among themselves. This does not 

 mean tliat the differences are less real, but I cannot dispell the 

 thought that these portions of the songs resembling the notes of 

 the presumed host species may have been due to the limiting condi- 

 tions of the aviary, whereas the "weaverbird-like" notes common to 

 all four species agree with what is known of their calls in the state 

 of nature. 



The very abbreviated form in which Nicolai's data were reported 

 caused them to appear to imply further evidence for a definite host- 

 parasite relationship, but this is not actually implicit in them. We 

 are not informed how many individuals of each species of viduine 

 were observed or under what conditions. Thorpe's (1958) work on 

 the learning of song patterns by small passerine birds, especially the 

 chaffinch, has indicated that the learned, as opposed to the innate, 

 pattern of song is restricted to the "first 13 months of life and towards 

 the end of this time there is a peak period of learning activity of a 

 few weeks during which a young Chaffinch may learn, as a result 

 of singing in a territory, the fine details of as many as six different 

 songs." If Nicolai's assumption is correct, that the young parasitic 

 widowbirds learn the utterances of their foster parents during the 

 first two or three weeks of life, they are apparently more precocious 

 than chaffinches in this respect. Furthermore, we may recall that 

 in the case of parasitic cowbirds and cuckoos there is no sign what- 

 ever of the young learning any of the vocalisms of their fosterers. 

 This cannot be looked upon as meaning that the same situation 

 necessarily is true for the parasitic weavers, but judgment must be 

 delayed until evidence is forthcoming. If eventual fuller publication 

 of Nicolai's work should convince us that the viduines enhance their 

 reproductive potential even very slightly by vocal mimicry of their 

 common hosts, we would have to admit an unexpected uniqueness in 

 these birds. 



Another study that appeared too late for me to discuss in my ac- 

 count was Ziswiler's (1959) paper on features of the ontogenetic 

 development of the waxbills. While presenting some data on the 

 relative lack of sensitivity of later developmental stages to increas- 

 ingly long interruptions of brooding, and also some data on the 

 postembryonic (i.e., nestling) growth curves of several species, 

 Ziswiler does not concern himself with the viduines at all ; he does not 

 even mention them. His paper therefore gives us no opinions to eval- 



