83 ICTERID^E. 



grown-up young like other species, and tins might have made me 

 suspect that they did not hatch their own eggs ; but it never occurred 

 to me that the bird was parasitical, I suppose because in summer they 

 are always seen in pairs, the male and female being inseparable. 

 Probably this is the only parasitical species in which there is conjugal 

 fidelity. I also noticed that, when approached in the breeding- season, 

 the pair always displayed great excitement and anxiety, like birds that 

 have a nest, or that have selected a site on which to build one. But 

 year after year the end of the summer would arrive, the birds reunite 

 in parties of half a dozen, and the mystery remain unsolved. At length, 

 after many years, fortune favoured me, and while observing the habits 

 of another species (Molothrus badius), I discovered by chance the 

 procreant habits of the Screaming Cow-birds ; and as these observations 

 throw some light on the habits of M. badius, I think it best to transcribe 

 my notes here in full. 



A pair of Lenateros (Anumbius acuticaudatus) have been nearly all 

 the winter building a nest on an acacia tree sixty yards from the house ; 

 it is about 27 inches deep, and 16 or 18 in circumference, and appears 

 now nearly finished. I am sure that this nest will be attacked before 

 long, and I have resolved to watch it closely. 



September 28. To-day I saw a Bay-wing (M. badius) on the nest ; 

 it climbed over it, deliberately inspecting every part with the critical air 

 of a proprietor who had ordered its construction, taking up and re- 

 arranging some sticks and throwing others a\\ ay from the nest. While 

 thus engaged, two common Cow-birds (M. bonariensis) , male and female, 

 came to the tree ; the female dropped on to the nest, and began also to 

 examine it, peering curiously into the entrance and quarrelling with 

 the first bird. After a few minutes she flew away, followed by her 

 glossy consort. The Bay-wing continued its strange futile work until 

 the owners of the nest appeared, whereupon it hopped aside in its usual 

 slow leisurely manner, sang for a few moments, then flew away. The 

 similarity in the behaviour of the two birds struck me very forcibly ; 

 in the great interest they take in the nests of other birds, especially in 

 large covered nests, the two species are identical. But when the 

 breeding-season comes their habits begin to diverge : then the Common 

 Cow-bird lays in nests of other species, abandoning its eggs to their 

 care ; while the Bay-wings usually seize on the nests of other birds and 

 rear their own young. Yet, as they do occasionally build a neat 

 elaborate nest for themselves, the habit of taking possession of the nests 

 of other birds is, most likely, a recently acquired one, and probably its 

 tendency is to eradicate the original building instinct. 



October 8. This morning, while reading under a tree, my attention 



