Vol.^vi. I Barrett, Parasitical Habits in the- Ciiculidce. ^J 



this particular Cuckoo would, if a female, sometimes deposit an 

 egg in the nest of a bird belonging to the species amongst 

 whom her infancy was passed ? The Cuckoo would also 

 naturally transmit this predilection to her own offspring, and 

 they in turn would rear young, or leave them to be reared by 

 foster-parents, endowed with the same inclination towards para- 

 sitism. As time went on, and successiv/e generations of Cuckoos 

 from the same parent stock had been born and died, the para- 

 sitical instinct would gradually become more pronounced in the 

 family, and, being an aid to its preservation and perpetuation, 

 would finally become a fixed, immutable instinct. 



As a proof of this theory I may cite the peculiar habits of 

 certain species of the American IcteridcB or Cow-Birds {Molo- 

 tJirus), which, according to Mr. W. H. Hudson, author of "The 

 Naturalist in La Plata" (with whom I am in correspondence), 

 are only partially parasitical, being apparently still at the half- 

 way house between virtue and vice. The Cow-Birds live 

 together promiscuously, in flocks composed of many individuals 

 of both sexes, and either build a nest for themselves or forcibly 

 seize upon a suitable one belonging to some unfortunate member 

 of another family of birds. In the event of there being either 

 eggs or young in the appropriated nest the feathered robbers 

 proceed to cast them out — a first trace of the ejecting instinct — 

 before laying their own eggs therein. Strangely enough, Cow- 

 Birds will sometimes construct a loose, untidy nest for them- 

 selves on top of a stolen one, without making use of the latter 

 for purposes of nidification. One species of MolotJirus has the 

 parasitical habit much more strongly developed than other 

 members of the genus, as it almost invariably lays its eggs in 

 the nests of other birds ; but sometimes several individuals will 

 club together and attempt the construction of a large, shapeless 

 nest, which, however, is never completed or made use of. These 

 strange birds frequently lay as many as 20 eggs in a single nest, 

 and they also possess the remarkable habit of piercing holes 

 with their bills either in their own eggs or in those of other 

 birds. Another curious fact relating to Cow-Birds is that one 

 species (yW. riifaxillaris) is actually parasitic upon another 

 member of the same genus {M. badius), which builds its own nest. 



Additional proof of the gradual development of parasitism 

 among the Cucididce is found in the fact that an American 

 Cuckoo {Coccj::ns americanus), which, as a general rule, builds a 

 nest and rears its own offspring, has yet been known to depart 

 from its normal habit in this respect, and leave its pale green egg 

 in an alien nest. The Hawk-Cuckoos {Hierococcyx) of southern 

 India, which exactly resemble both in colour and flight the 

 Sparrow-Hawks of that region, furnish still another instance. 

 Of the six known species of Hierococcyx one only is said to build 

 a nest, the remaining five being parasitic on the Babbling- 



