488 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
hypothesis was reasonable enough, as, personally, he could not re- 
member ever having witnessed a young cuckoo being tended by any 
but soft-billed insectivorous birds. He adds, very quaintly, that the 
depositing of its eggs by the cuckoo in another bird’s nest is such a 
monstrous outrage on maternal affection that, had it been related of a 
bird in the Brazils or Peru, it would not have merited belief. On 
October 8, 1770, the observant old naturalist again writes, this time 
from Ringmer, in Sussex, to the effect that he has just seen a young 
cuckoo in a lark’s nest, and that it was very pugnacious, pursuing his 
finger and buffeting and sparring with its wings like a game cock. 
T have often noticed this bad-tempered disposition myself amongst our 
Victorian species, and it seems to be quite in accordance with the 
general nature of the birds as a class. 
Coming to more recent time, we find Charles Darwin, in his chapter 
on instinct in the “ Origin of Species,” throwing the searchlight of 
his genius into the dark corners of the cuckoo problem. Variation 
~ and natural selection, the great naturalist considers, have undoubtedly 
been the main factors in building up the parasitical instinct which we 
see working in all its horrible perfection to-day. Let it be supposed, 
for instance, that an early progenitor of our lovely little shining 
bronze cuckoo (Chalcococcyx plagosus) occasionally departed from 
the natural order of things, and deposited one of her tiny eggs in the 
nest of some other species of bird, either accidentally or by reason 
of being compelled to lay before her own nest was completed, just as 
to-day we frequently find the pale blue eggs of starlings and mynahs 
scattered about the open fields or on our suburban lawns. If we con- 
ceive further that the egg thus consigned to its fate in an alien nest 
has duly brought forth a baby cuckoo, which, being reared by the 
foster-parents, has unconsciously acquired, during the nestling period, 
a predilection for the company of its foster-parents and their kind, is 
it not probable that this particular cuckoo would, if a female, some- 
times deposit an egg in the nest of a bird belonging to the species 
amongst whom her infancy was passed? The cuckoo would also nat- 
urally 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 toward parasitism. As time 
went on, and successive generations of cuckoos from the same parent 
stock had been born and died, the parasitical instinct would gradually 
become more pronounced in the family, and, being an aid to its pres- 
ervation 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 Icteride or cowbirds (Jolothrus), which, 
according to Mr. W. H. Hudson, author of “The Naturalist in La 
