56 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



The problem of egg morphism, is, as we have seen, not a prominent 

 one in the genus Clamator. Still, by virtue of what it reveals in 

 Cuculus, where it is well developed, it raises one further point that 

 is worth discussing here. In the European Cuculus canoriis we have 

 a species with a wide range of eggshell coloration, and we have rea- 

 sonably good evidence for the existence within the species of numbers 

 of different gentes, each specific on a definite host species. The 

 existence of two or more gentes sympatrically increases the efficiency 

 of each in exploiting host egg mimicry, and allows a greater popula- 

 tion of cuckoos to exist in a limited area. Regardless of the reality 

 of these gentes, and no doubts as to their existence are here implied, 

 it is true that the only way in which we may be made aware of them 

 is by the fact that each individual hen cuckoo lays a single egg type, 

 and is specific in its host choice, while the species lays a wide range of 

 eggs and uses many species of hosts. From this it follows that if 

 Cuculus canorus laid but a single type of egg it could still have gentes, 

 but we would be unable to sense their existence and would have no 

 reason even to conceive that there might be any. In the crested 

 cuckoos of the genus Clamator we have seen that each species has 

 but a single egg type, except for incipient variation in levaillantii and 

 geographic variation in jacobinus. Consequently, no suggestion of 

 gentes has ever been raised in studies of this genus, and, indeed 

 there would seem to be nothing on which natural selection might 

 have favored the development of such infraspecific categories. Still, 

 we cannot rule out the possibility that the hens of each of the four 

 species may be individually host specific (as in glandarius in the 

 Iberian peninsula, where all the hens are essentially specific on the 

 same host, the magpie). If this should prove to be the case, we would 

 have, in effect, undistinguishable but yet actual gentes in the species 

 of Clamator. 



In this connection we may recall Southern's (1954, p. 223) con- 

 clusion about gentes in Cuculus canorus to the effect that those gentes 

 which are highly adapted in egg mimicry probably thereby sacrifice 

 a certain degree of what plasticity their ancestors may have had, and 

 with it the ability to turn successfully to new and very different hosts. 

 In effect, Clamator glandarius in the Iberian Peninsula and in ad- 

 jacent parts of western Mediterranean Africa is comparable to a 

 single highly specialized gens in Cuculus canorus. Yet it has been 

 able to utilize remarkably dissimilar hosts in sub-Saharan Africa. 



Whereas in Cuculus there is a definite trend for small egg size, 

 relative to the size and weight of the adult bird, a trend which has 



