NO. 4 AVIAN GENUS CLAMATOR — FRIEDMANN 57 



enabled the members of that genus to parasitize birds much smaller 

 than themselves, no such reduction in relative egg size is found in 

 Clamator. For that matter, diminution of egg size is found in all 

 species of Cuculus, but not in other genera of parasitic cuckoos. 

 Within the species Clamator jacobinus we do find a slight geographic 

 reduction in egg size, but nothing comparable to the situation in 

 Cuculus. The greenish-blue eggs of C. j. pica average slightly smaller 

 than do the white ones of C. j. serratus, but the difference, while 

 significant and, in an evolutionary sense, suggestive, is not trenchant 

 as there is extensive overlap in the sizes of the two groups. Thus, 

 eggs of southern African serratus vary from 24.1 to 28 by 20.8 to 

 23 mm., with an average of 25.5 by 22 mm. ; while those of pica 

 from Ethiopia vary from 22 to 25 by 20 to 22 mm., with an average 

 of 23.5 by 20 mm., and eggs of pica from India range from 21.9 

 to 28 by 17.6 to 21.4 mm., with an average of 24.3 by 19.4 mm. The 

 eggs of south Indian, nominate jacobinus are slightly smaller still, in 

 keeping with the lesser size of the birds of that race. 



The development of brood parasitism and the varying features it 

 exhibits in different genera of cuckoos make it clear that each genus 

 needs to be studied independently before we may attempt to gen- 

 eralize. In Clamator the evolutionary history of the egg size and 

 coloration differs from that in Cuculus; it reveals no marked reduc- 

 tion in size and while it has achieved remarkable adaptive similarity 

 to those of its hosts in color it has done this without developing 

 any extensive egg morphism within any of its species. 



INCUBATION PERIOD 



Rapid development of the embroyos, or shortening of the incuba- 

 tion period of the eggs, is generally considered as advantageous to a 

 parasitic bird, as it may result in the parasite hatching before its nest- 

 mates and thereby gaining a "start" on them. This would seem par- 

 ticularly pertinent to parasites that do not attempt to evict their nest- 

 mates but grow up with them. If this concept were infallible we 

 might expect to find a slight, but significant, change in this direction 

 from the most primitive species of Clamator, the pied cuckoo, C. 

 jacobinus, to the most advanced, the great-spotted cuckoo, C. glan- 

 darius. The few facts available, are, surprisingly enough, contrary to 

 this postulated condition. The incubation period for jacobinus, as 

 worked out carefully by Liversidge (1961, p. 624) in four instances, 

 was between 11 days ±14 hours and 12 days ±12 hours, while in 

 glandarius, Mountfort (1958, pp. 54-56) found it to be 14 days. As 

 yet, no data are available on the other two species. 



