AVIAN GENUS CHRYSOCOCCYX 91 



Host -parasite nestling relations 



Aside from the evicting habit by which the young cuckoo eliminates 

 its nest-mates (discussed in the next section), a few other aspects of 

 the nest-inhabiting period of the parasite's life call for comment. 

 Although the available data are still incomplete, they are here given 

 more as a basis for future additions than as a statement of any finality. 

 The topics of biological interest are: the length of the incubation period 

 of the cuckoo's eggs, the diu*ation of the nestling stage, and the dura- 

 tion of attentive behavior on the part of the host after the young 

 parasite is fledged, i.e., after it leaves the nest. 



The incubation period has not been reported for any of the glossy 

 cuckoos except C. caprius, and in that species the few published state- 

 ments are not at all harmonious. Skead (1947, pp. 23-24) A\Tote that 

 the incubation period was lOJ^ days (in a nest of the Cape weaver, 

 Ploceus capensis olivacens). From piece-meal data on several nests 

 containing caprius eggs, I estimated (1949a, p. 163) it to be a day 

 longer. More recently, Hunter (1961, pp. 55-63) studied the para- 

 sitism of caprius on the masked weaver, Ploceus velatus, and concluded 

 that the eggs of the cuckoo took about 12 days to hatch. In the case of 

 C. osculans, Chisholm (1935, p. 70) wrote of a nest of a speckled war- 

 bler, Chthonicola, with an egg of osculans and stated that "two weeks 

 later the egg had hatched. . . ." This is the nearest to a statement 

 of the incubation period I have found for this species, and it was not 

 written as an accurate, precise measurement. Inasmuch as any short- 

 ening of the incubation period would seem to be a selectively critical 

 factor in a group of brood parasites, it would be very interesting to 

 know if the glossy cuckoos reveal any adaptive differences, even slight, 

 in the duration of their prenatal development. It is not clear from 

 present fragmentary data if we can assume that the incubation period 

 is shorter in caprius than in osculans; more data on these two and on 

 the other species of the group are needed. 



The dm-ation of the nesthng stage (from hatching to fledging) has 

 not been recorded for any of the Austrahan and Asian species of 

 Chrysococcyx; in the case of klaas the nestling period was at least 

 12 days in a nest of the amethyst sunbnd, Chalcomitra amethystina 

 and it was suggested (Friedmann 1949a, p. 146) that the exact length 

 of the period might vary somewhat vnth different species of fosterers. 

 In caprius, Skead (1947, pp. 23-24) found the nestling period, wdth 

 the Cape weaver as a host, to be 10 to 15 days; Pitman (in Friedmann 

 1949a, pp. 180-181) found a young caprius, about a fortnight old, 

 in a nest of a sunbird, Nectarinia erythroceria, while Hunter (1961) 

 found that a young caprius remained in the nest of a masked weaver 

 for 20 days. R. A. Reed (in litt.) found a young didric, C. caprius, 



