612 REPORT OF NATIONAL MUSEUM, 1893. 



many cases a knowledge of the disused instincts will assist us very 

 materially in the inquiry. I will illustrate my meaning- with a suppo- 

 sititious case. Should all or many species of Cohimhidw manifest au 

 inclination for haunting rocks and banks, and for entering or peering 

 into holes in them, such vague and purposeless actions, connected with 

 the facts that all doves build simple platform nests (like Columha liria 

 and others that build on a flat surface), also lay white eggs (the rule 

 being that eggs laid in dark holes are white, exposed eggs colored), also 

 that one species, C. liria, does lay in holes in rocks, would lead us to 

 believe that the habit of this species was once common to the genus. 

 We should conclude that an insufficiency of projjer breeding places, 

 i. e., new external conditions, first induced doves to build in trees. 

 Thus C. liria also builds in trees where there are no rocks; but, when 

 able, returns to its ancestral habits. In the other species Ave should 

 believe the primitive habit to be totally lost from disuse, or only to 

 manifest itself in a faint, uncertain manner. 



!N'ow, in Molothnis b(>)iarienfiis we see just such a vague, purpose- 

 less habit as the imaginary one 1 have <lescribed. Before and dur- 

 ing the breeding season the females, sometimes accompanied by the 

 males, are seen continually haunting and examining the domed nests 

 of some of the Bendrocolaptida'. This does not seem like a mere 

 freak of curiosity, but their persistence in their investigations is 

 precisely like that of birds that habitually make choice of such 

 breeding places. It is surprising that they never do actually lay in 

 such nests, ex(;ept when the side or dome has been accidentally 

 broken enough to admit the light into the interior. AVhenever I set 

 boxes up in my trees the female Cowbirds were the first to visit them. 

 Sometimes one will spend half a day loitering about and inspecting a 

 box, repeatedly climbing round and over it and always ending at 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 spa(;e she will return again and again, as if fascinated with the 

 comfort and security of such an abode. It is amusing to see how per- 

 tinaciously they hang about the ovens of the Ovenbirds, apparently 

 det rmined to take jiossession of them, flying back after a hundred 

 repnlses, and yet not entering them even when they have the oppor- 

 tunity. Sometimes one is seen following 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 .1/. 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 1 can scarcely doubt; at least, to no other cause that I can 

 imaguie can it be attributed; and, besides, it seems to me that if M. 

 bonarieiifiis, when once a nest builder, had acquired the semiparasiti- 

 »m1 habit of breeding in domed nests of other birds, such a habit 

 might conduce to the formation of the instinct which it now possesses. 



