io8 BIRDS OF LA PLATA 



and I looked forward to the next summer to work 

 out the rich mine on which I had stumbled by chance. 

 Unhappily when spring came round again ill-health 

 kept me a prisoner m the city, and finding no im- 

 provement in my condition, I eventually left Buenos 

 Ayres at the close of the warm season to try whether 

 change of climate would benefit me. Before leaving, 

 however, I spent a few days at home, and saw enough 

 then to satisfy me that my conclusions were correct. 

 Most of the birds had finished breeding, but while 

 examining some nests of Anumbius I found one 

 which Bay-wings had tenanted, and which for some 

 reason they had forsaken, leaving ten unincubated 

 eggs. They were all like Bay-wings' eggs, but I have 

 no doubt that five of them were eggs of M. rufo- 

 axillaris. During my rides in the neighbourhood I 

 also found two flocks of Bay-wings, each composed 

 of several families, and amongst the young birds I 

 noticed several individuals beginning to assume the 

 purple plumage, like those of the previous autumn, 

 I did not think it necessary to shoot more specimens. 



The question why M, badius permits M, rufo- 

 axillaris to use its nest, while excluding the allied 

 parasite M. bonariewis, must be answered by future 

 observers ; but before passing from this very inter- 

 esting group (Molothrus) I wish to make some general 

 remarks on their habits and their anomalous relations 

 to other species. 



It is with a considerable degree of repugnance 

 that we regard the parasitical instinct in birds ; the 

 reason it excites such a feeling is manifestly that it 



