ARGENTINE COW-BIRD 91 



the entrance, into which she peers curiously, and 

 when about to enter starting back, as if scared at 

 the obscurity within. But after retiring a little space 

 she will return again and again, as if fascinated with 

 the comfort and security of such an abode. It is 

 amusing to see how pertinaciously they hang about 

 the ovens of the Oven-birds, apparently determined 

 to take possession of them, flying back after a hundred 

 repulses, and yet not entering them even when they 

 have the opportunity. Sometimes one is seen follow- 

 ing a Wren or a Swallow to its nest beneath the eaves, 

 and then clinging to the wall beneath the hole into 

 which it disappeared. 



I could fill many pages with instances of this habit 

 of M. bonariensis, which, useless though it be, is as 

 strong an affection as the bird possesses. That it is 

 a recurrence to a long disused habit I can scarcely 

 doubt ; at least to no other cause that I can imagine 

 can it be attributed ; and besides it seems to me 

 that if M. bonariensis, when once a nest-builder, had 

 acquired the semi-parasitical habit of breeding in 

 domed nests of other birds, such a habit might 

 conduce to the formation of the instinct which 

 it now possesses. I may mention that twice I 

 have seen birds of this species attempting to 

 build nests, and that on both occasions they failed 

 to complete the work. So universal is the nest- 

 making instinct that one might safely say that the 

 M. bonariensis once possessed it, and that in the 

 cases I have mentioned it was a recurrence, too 

 weak to be efficient, to the ancestral habit. 



