SCREAMING COW-BIRD 107 
rarely, pale blue. It is not possible to confound the 
eggs of the two species. Now ever since I saw, many 
years ago, the Yellow-breast feeding the supposed 
young Bay-wings, I have looked out for the eggs of 
the latter in other birds’ nests. I have found hundreds 
of nests containing eggs of M. bonariensis, but never 
one with an egg of M. badius, and, I may now add, 
never one with an egg of M. rufoaxillaris. It 
is wonderful that M. rufoaxillaris should lay only 
in the nests of M. badius ; but the most mysterious 
thing is that M. bonariensis, indiscriminately para- 
sitical on a host of species, never, to my knowledge, 
drops an egg in the nest of M. badius, unless it be 
in a forsaken nest! Perhaps it will be difficult for 
naturalists to believe this; for if the M. badius is so 
excessively vigilant and jealous of other birds ap- 
proaching its nest as to succeed in keeping out the 
subtle, silent, grey-plumaged, omnipresent female 
M. bonariensis, why does it not also keep off the far 
rarer, noisy, bustling, conspicuously coloured M. 
rufoaxillaris? I cannot say. The only explanation 
that has occurred to me is that M. badius is sagacious 
enough to distinguish the eggs of the common parasite 
and throws them out of its nest. But this is scarcely 
probable, for I have hunted in vain under the trees 
for the ejected eggs; and I have never found the 
eggs of M. badius with holes pecked in the shells, 
which would have been the case had a M. bonariensis 
intruded into the nest. 
With the results just recorded I felt more than 
satisfied, though much still remained to be known; 
