'J^i SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



strictly migratory in some parts of their respective ranges and not 

 in other parts. ( In the case of C. coromandus, the available evidence 

 is not conclusive about an area of permanent residence, and, hence, 

 of a population of nonmigratory birds.) The extent of migratory 

 movement varies from none at all to thousands of miles. All three 

 of the species breeding in South Africa {glandarius, jacobinus, and 

 levaillantii) are absent from that area during the southern winter ; 

 all three have resident populations in tropical Africa. The first named 

 of these is present in its Mediterranean breeding grounds in the 

 Iberian Peninsula and northwestern Africa only during the northern 

 summer, and then migrates to equatorial parts of Africa, apparently 

 chiefly in the eastern half of the continent. The migration of this 

 section of the species is thus exactly the opposite, both in direction 

 and in time of the year, from that of the South African glandarius. 

 In other words, we find in these cuckoos that geographic segments, 

 not necessarily even subspecifically distinct, differ markedly from 

 other conspecific segments in their migratory behavior. It need hardly 

 be added that in the majority of birds that have spatially distinct 

 breeding and nonbreeding quarters, migration is an important, well- 

 formulated and patterned, presumably evolved and inherited, part of 

 their annual life cycle. Yet in the crested cuckoos of the genus 

 Clamator, this migratory behavior is manifested only in sections of 

 each of the included species. 



In this geographic fragmentation of migratory behavior within the 

 members of each species, we have something that may be likened to 

 partial migration, with the difference that here the "partial" element 

 is geographic, not individual. Partial migration is a term used chiefly 

 for species in which some individuals are regularly migratory while 

 others, breeding in the same area, are nonmigratory, resident birds. 

 Inasmuch as there is no evidence to prove that the migratory South 

 African populations are ecologically or geographically cut off from 

 their nearest resident counterparts in tropical Africa, we cannot 

 postulate an interference effectively isolating them into discrete, non- 

 intercommunicating colonies or gene pools. Even allowing for a 

 reduced frequency of such intercommunication, we may come back 

 to something akin to partial migration (in an overall species view) as 

 a valid way to express their migratory tendencies. 



Partial migration of the more usual sort has been studied in the 

 North American song sparrow by Nice (1937), and in a variety of 

 European passerine species by Lack (1943-44). Their findings are 

 of interest here. Nice (1937) found that in the song sparrow, 



