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 f 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 I 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 t 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; 



