60 U.S. NATIONAL MUSEUM BULLETIN 265 



Ploceus velatus: races velatus and nigrijrons 



Ploceus cucullatus: races cucullatus, collaris, bohndorffi, graueri, 



nigriceps, and spUonotus 

 Ploceus nigerrimus: races nigerrimus and castaneofuscus 

 Ploceus melanocephalus: races capitalis, duboisi, and dimidiatus 

 Euplectes hordeaceus: races hordeaceus and craspedopterus. 



Host Specificity 



Avian brood parasites fall into three categories as far as host 

 specificity is concerned: those that exhibit no such specificity, those 

 that are specific in their parasitism as individuals only, and those 

 in which the entire species is specific on one host species or a small 

 group of related hosts. Members of the first category deposit their 

 eggs in any available and generally suitable nest, regardless of the 

 particular species of victim involved; this is true not only of the brood 

 parasite as a species but also of each of its included individuals. 

 These may be said to be nonhost specific. 



Parasites whose individual members tend to lay all their eggs in 

 nests of a single species of host, although the hosts may differ for 

 many of these conspecific parasites, may be described as exhibiting 

 individual host specificity. In some such cases there may be adaptive 

 development of egg morphs with resemblance to the eggs of frequent 

 fosterers. In the case of the European cuckoo, the best known example 

 of individual host specificity, the individually host-specific producers 

 of these ovomorphs have been termed "gentes," groups intermediate 

 between morphs and geographical subspecies. Southern (1954, p. 220) 

 considered that about half the species of parasitic cuckoos sufficiently 

 studied have been found to have, or are suspected to have, such 

 subdivisions. This conclusion seems to be an exaggeration and possibly 

 was derived by counting as species some of the Asiatic races of 

 Cuculus canorus, such as telephonus and bakeri, and putting them 

 together with other species that lay but a single egg type that matches 

 the eggs of its regular hosts (e.g., Cuculus optatus), It seems better 

 to consider the ovomorphic gentes of Cuculus canorus and of Cuculus 

 micropterus as the extreme of adaptive evolution rather than as a 

 widespread condition in the cuckoos. The condition in Chrysococcyx, 

 outlined below and in our discussion of egg morphism, helps to put 

 this in proper perspective. 



The third group, characterized by specific-host specificity, comprises 

 species in which the individual host preferences of all the included 

 members are similar, with the result that the species of parasite is 

 restricted in its parasitism to a single species or to a small group of 

 similar species of hosts. It would seem (but cannot be proved) that in 



