AVIAN GENUS CHRYSOCOCCYX 61 



some of the cuckoos' specific-host specificity is an evolutionary out- 

 growth from an earlier individual host specificity. 



All three stages of host specificity are to be found in the glossy 

 cuckoos. It must be said, however, that in such cases the "evidence" 

 for nonhost specificity is an inference based only on the fact that in 

 many places egg collectors and other nest observers have recorded a 

 variety of parasitized nests without significant percentages of dupli- 

 cation of hosts \\dthin a Umited area or over a limited time of observa- 

 tion. Careful, intensive field studies may reveal more actual or 

 incipient individual host-specific trends than these present records 

 suggest. Actually, we know that many brood parasites with a A\ide 

 range of host species tend to utilize only a fraction of them with marked 

 regularity. Thus, in the case of nonhost specific cuckoos, the lack 

 of observable individual host preferences seems due, not necessarily 

 to their definite absence, but to the fact that, while such preferences 

 or specificities may be present as a "background" situation, they are 

 rather easUy ignored when a suitable nest of a different potential 

 host becomes available, particularly when nests of favorite hosts are 

 scarce. It may well be that some of these hen cuckoos have potential 

 individual host jDreferences, but that these have not become fLxed or 

 rituaHzed to a degree where they impose an obligatory direction, 

 and hence they are not a^^parent to the observer — and this is aU 

 that is implied when such cuckoos are described as nonspecific in 

 their host selection. 



In two sympatric Austrahan glossy cuckoos, basalts and lucidus, 

 we find a difference in manner of host choice that may reflect one 

 factor under the influence of which individual host specificity may 

 have developed. C. lucidus very frequently (but not always) uses 

 spherical, or at least dome-shaped, nests while basalis appears to be 

 free from any such restriction, selecting both domed and open nests 

 equaU}''. This means that lucidus is thereby rendered more Umited in 

 its choice of hosts than is basalis. However, the number of available 

 fosterers as nest-builders in either category is still considerable, but 

 even Anthin the domed-nesting species a difference exists in the Hst 

 of fosterers frequently imposed upon by the two cuckoos. Thus, 

 Serventy and Whitell (1962) write that basalis parasitizes the banded 

 whitef ace, Aphelocephala nigrocincta, western warbler, Gerygone fusca, 

 blue wren, Malurus cyaneus, white Avinged WTcn, Malurus cyanotus, 

 blue and white WTen, Malurus leucopterus, variegated Avren, Malurus 

 lamberti, striated field \xven, Calamanthus fuliginosus, MaUee heath 

 Avren, Hylacola cauta, brown thornbiU, Acanthiza pusUla, and yellow- 

 tailed thornbill, Acanthiza chrysorrhoa. Of these the two thornbills 

 (especially the yellow-tailed one) and the blue wren are also Hsted as 



