64 U.S. NATIOXAL IVIUSEUM BULLETIN 265 



5. C. maculatus: no reliable or even inferential information. The 

 similarity of its eggs to those of its Arachnothera host may suggest 

 a trend toward specificity, but there are no critical data. 



6. C. xanthorhynchus: as in C. maculatus. 



7. C. Haas: meager data and the fact that no egg resemblance has 

 been developed with reference to the majority of its numerous species 

 of hosts make it difficult to argue for marked host specificity in this 

 cuckoo. However, Pitman (1957) examined 100 nests of Prinia suhflava 

 at Broken Hill, Zambia, and found 7 of them to contain one klaas 

 egg each, all of one coloration type, suggesting that one, or a very few, 

 hens there were more or less specific on this longtail, or at least favored 

 it as a host. 



8. C. cwpreus: no data other than the vague suggestion of possible 

 individual host specificity underlying the observable egg adaptation 

 toward two of its numerous hosts. 



9. C. caprius: as indicated in our discussion of the egg morphism of 

 the didric cuckoo, the development of host-egg resemblance for two 

 of its commonly used fosterers, Eupledes orix and Passer melanurus, 

 and the large number of instances of parasitism on each of these, 

 suggests a considerable frequency of individual host specificity in this 

 cuckoo. The absence of such adaptive coloration in those eggs laid in 

 the nests of a great number of its other hosts does not necessarily 

 indicate, however, an absence of host-specific trends in many other 

 didi'ic hens. This is particularly true in the case of didi'ics parasitic on 

 masked weavers, as discussed below. Because intensive field studies 

 of African birds are stiU few in number, observations directly sug- 

 gestive of host specificity in didric parasites are relatively scarce, but 

 the folloAving instances are pertinent. 



R. A. Reed {in litt.) kindly sent me a transcript of his observations 

 made at "Tonqani," near Johannesburg, Transvaal. Over a period of 

 years he studied a number of colonies of red bishops, Euplectes orix. 

 In the 1955 season he regidarly inspected every nest in five colonies 

 of these birds, recording incubation and fledging periods. Not once 

 during the summer did he find a didric cuckoo egg or chick in any of 

 them, although adult didrics were commonly seen about there. These 

 same colonies had been heavily parasitized by the didrics the previous 

 year, but in 1955 the cuckoos concentrated on Cape sparrows, Passer 

 melanurus. This indicates that within one season several didric hens 

 were markedly specific on red bishops (1954), and that the next year 

 the same or, more probably, other didric hens were equally inclined 

 to use the nests of the Cape sparrow. In both seasons it seems some 

 hens were markedly host specific. A comparable case is that of G. Duve 

 (in litt), also near Johannesburg, who found that some didrics, laying 

 plain blue eggs, were parasitic on red bishops almost exclusively. 



