112 U.S. NATIONAL MUSEUM BULLETIN 2 65 



layardi in New Caledonia, New Hebrides, and the Loyalty Islands and harterti 

 on Rennell and Bellona Islands. The two Asiatic species, maculatus and xantho- 

 rhynchus, appear to be ecologically and altitudinally largely allopatric, but not 

 rigidly so (xanthorhynchus has a range that extends far beyond that of maculatus 

 to the east, encompassing areas as distant as Borneo and the Philippines, but 

 this is something beyond the contiguous allopatry the two species show in south- 

 ern Asia). The breeding range of osmilans implies an extensive area of allopatry 

 in spite of its southern sympatry with basalts and lucidus plagosus. 



In view of the fact that the point of origin, geographically and phylogenetically, 

 is only inferential in all the 12 species of the group, the only safe conclusion that 

 may be drawn from their current dispersal is that the several species each went 

 their own way witli no discernible repetition of any generic pattern. The variety 

 of their geographic dispersal is a telling, though commonplace, commentary on 

 the opportunistic aspect of evolutionary history. 



When one says that eacli species of Chrysococcyx has gone its own way, this 

 does not imply any incipient, directive "way" peculiar to each. This becomes 

 clear when the morphological characters of the geographic races of any of the 

 polytypic species of the genus are examined. Thus, to take but one instance, the 

 variations in the distribution of rufescent coloration in the rectrices of some of 

 the subspecies of vialayanus are not selectively "adaptive"; they are not characters 

 that help to make their bearers more or less fitted for the particular places in 

 which they live. If these characters were plotted on a map they would show no 

 progressive, rectilinear, or orthogenetic correspondence with the geographic, 

 spatial relations of the races. The emergence of these slight differences as constantly 

 recurring phenotypes is merely the result of each population's having had to 

 utilize the fragment of the total gene pool of the species available to it. The 

 possibility exists that these external characters, while diagnostic in the museum 

 sense, are not selectively important in themselves but that they may be the 

 outward manifestations of genes that have some adaptive value. This is, ad- 

 mittedly, beyond the capability of present evidence to prove or to disprove, but 

 the thought should be kept in mind. The "way" of each species is, not what it 

 "set out to do or to be, but what has happened to it." 



The high incidence of sympatry in the glossy cuckoos causes one to ask if these 

 birds have not yet achieved their final, biologically "perfected" stage, especially 

 since in many instances (plagosus, basalis, and osculans; klaas and caprius) they 

 are partly homoxenic (sharing the same hosts), even if they show trends toward 

 alloxenia (using different hosts). If their geographical and ecological sympatry 

 were accompanied by highly developed and rigidly regulated alloxenia, these 

 coexisting species of Chrysococcyx would be, as far as their breeding is concerned, 

 distinctively separated, even though their hosts were sympatric. Such a con- 

 dition does obtain in some avian arthropod ectoparasites, as was shown by Clay 

 (1949), and such reproductive differentiation would in itself suffice to counteract 

 the Gauseian principle that two or more kinds of related animals with identical 

 or very similar ecological requirements are not able to coexist indefinitely because 

 one of them wUl prove more efficient than the other and thus will displace the 

 latter. The glossy cuckoos are possibly still on the way toward the eventual 

 circumvention of this situation. 



On the other side of the picture, it appears that in all these cases of sympatric 

 species of glossy cuckoos the forms involved have complete specific independence. 

 So far as I have been able to learn (and I have examined several thousands of 

 specimens in all), no instances of hybridization have been found between any 

 of them. Furthermore, I know of no observations of mixed courtship behavior, 

 although there often is no ecological or other habitat isolation to prevent it. 



