AVIAN GENUS CHRYSOCOCCYX 83 



bill, and placed it in the Robins' nest — leaving the two Robin eggs as 

 they were. The Robins worried the Cuckoo the whole time, until it 

 disappeared, after which the hen returned to the nest as if nothing 

 untoward had happened . . . ."In this case the nest was on the 

 ground and able to withstand the weight of the parasite had it entered 

 to lay an egg. 



Another less conclusive instance of mandibular oviposition by 

 C. basalis may also be recalled, A. C. Allen (reported by Ross 1946, 

 pp. 246-247) saw one of these cuckoos on the ground with an egg in 

 its mouth. Two blue wrens, Malurus cyaneus, nesting nearby were 

 much excited by the presence of the parasite, "which soon flew to a 

 small scrub and perched on the side of a nest. It stayed there for 

 about a minute making convulsive movements with its body and 

 flapping its wings. It then flew to an adjacent sapling, but the egg 

 had disappeared and the biU was closed. Mr. Allen then examined 

 the nest and it contained two eggs of a Wren and a white egg liberally 

 speckled with small red spots showing that the intruder was a Horsfield 

 Bronze-Cuckoo (Chalcites basalis) . . . ." In this instance the actual 

 insertion of the egg was not really observed, although the implication 

 of the account strongly suggested it. 



Still another case, called to my attention by K. A. Hindwood, may 

 be mentioned. Len Harvey (1961, p. 3) saw a female basalis carry her 

 own egg in her bill to a blue fairy wren's nest, and a few seconds later 

 the cuckoo flew off with one of the wren's eggs in her bill. This was at 

 Invermay, near Ballarat, Victoria. 



In Kenya and Uganda, Pitman {in litt.) concluded that C. Haas 

 probably also resorted to mandibular egg insertion into nests of some 

 of its sunbird hosts, although he did not have the good fortune to 

 observe such behavior. Others have made suuilar suggestions for 

 C. cupreus, although also without direct observations. 



By now we have seen that there is sufficient evidence to establish 

 the conclusion that mandibular egg placement does occur. By virtue 

 of the behavioral pliabflity behind this fact, nests that would otherwise 

 be unavailable to the cuckoos are made accessible for their parasitism. 

 It does appear, however, that this is an occasional rather than a 

 regular mode of egg laying. By and large, there is little reason to 

 assume that natural selection would ordinarily favor the evolution of 

 such a habit as a regular pattern, as it would seem to be connected 

 with a poor host choice. A bird nest too small to accommodate the 

 body of the parasitic hen would usually prove inadequate to hold the 

 young cuckoo after the first week or 10 days of its nestling growth. 

 Even Baker (1942, pp. 122-132), who was inclined to believe in 

 mandibular oviposition in a nest too small or too insecurely suspended 

 to bear the weight of an adult hen Cuckoo, attempted to use as "proof" 



