132 A HISTORY OF BIRDS 



more remarkable, since this bird lays its eggs in the nest of the 

 Black-drongo {Buchanga atra), a feat which it apparently could 

 not accomplish but for the fact that it has acquired a most 

 extraordinary resemblance to this bird, thereby enabling it to 

 evade the notice of the owners of the nest when about to thrust 

 upon them the doubtful privilege of incubating its eggs. But 

 of this particulars will be given elsewhere in these pages (p. 327). 

 In Java, however, it appears to dupe the Bulbul {Pymonotus 

 aurigaster), at any rate two eggs in the British Museum were 

 obtained from the nests of this bird. 



Though Cuckoos all over the world, and of widely different 

 genera, have acquired parasitic habits, some species build nests 

 and incubate their eggs in normal fashion, though, as a rule, 

 these nests are but indifferently constructed. This does not 

 apply, however, to the Lark-heeled Cuckoos of the Genus 

 Centropus, which build a large globular nest, generally with an 

 entrance at the side. 



One or two species at least, though commonly parasitic, 

 appear occasionally to build a nest and incubate. This is the 

 case, for example, with the Hawk Cuckoo {Hierococcyx spar- 

 veroides) of the Himalayas and East Asia, which appears to be 

 normally parasitic, but in the Nilgiris to build a nest and rear 

 its young. 



This strange aberration of the parental instinct is, however, 

 not confined to the Cuckoos, since it is met with also among the 

 South American " Hangnests," birds belonging to a widely 

 different group — being true Passeres. Thus one species 

 [Cassidix oryzivorus) in Pard appears always to leave the in- 

 cubation of its eggs and care of its young to an allied species, 

 C. persicus, while farther south it victimises others of about its 

 own size, such as the Crested Cassique {Ostiniops decumanus) or 

 the Yellow Cassique {"Cassicus hcsmorrhous). 



The nearly allied polyandrous " Cow-birds," belonging to 

 the Genus Molobrus, are yet more interesting from this point of 

 view, inasmuch as this parasitism appears to have brought 

 about a state of disorganisation of the parental instinct which 

 threatens all the species concerned with extinction. Only one 

 species, Molobrus badius, appears to have retained the normal re- 

 productive instincts. The rest seem to share in common the 

 habit of dropping a considerable number of their eggs in empty 



