MOLOTHRUS RUFOAX1LLARIS. 91 



distance from me, and I naturally concluded that they were young 

 Common Cow-birds (M. bonariensis), casually associating with the Bay- 

 wings. I was surprised to see them, for the young male M. bonariensis 

 always acquires the purple plumage before March, so that these 

 individuals were changing colour five weeks after the usual time. To- 

 day, while out with my gun, I came upon the flock, and noticed four 

 of the birds assuming the purple plumage, two of them being almost 

 entirely that colour ; but I also noticed with astonishment that they 

 had bay- or chestnut-coloured wings, also that those with least purple 

 on them were marvellously like the Bay-wings in the mouse-coloured 

 plumage of the body and the dark tail. I had seen these birds before 

 the purple plumage was acquired, and there was then not the slightest 

 difference amongst them, the adults and their supposed offspring being 

 alike ; now some of them appeared to be undergoing the process of a 

 transmutation into another species ! I at once shot the four spotted 

 birds along with two genuine Bay-wings, and was delighted to find that 

 the first were young Screaming Cow-birds. 



I must now believe that the extra eggs twice found in the nest of the 

 Bay-wings were those of the Screaming Cow-bird, that the latter species 

 lays chiefly in the nests of the former, that the eggs of the two species 

 are identical in form, size, and colour, each bird also laying five, and 

 that, stranger still, the similarity is as perfect in the young birds as it 

 is in the eggs. 



April 15. This morning I started in quest of the Bay- wings, and 

 observed one individual, that had somehow escaped detection the day 

 before, assuming the purple dress. This bird I shot; and after the 

 flock had resettled a short distance off, I crept close up to them, under 

 the shelter of a hedge, to observe them more narrowly. One of the 

 adults was closely attended by three young birds ; and these all, while 

 I watched them, fluttered their wings and clamoured for food every 

 time the old bird stirred on its perch. The three young birds seemed 

 precisely alike; but presently I noticed that one of them had a few 

 minute purple spots, and on shooting this one I found it to be a young 

 M. rufoaxillaris, while the other two were true young Bay-wings. 



The hunger-cry of the young M. badius (Bay- wing) is quite different 

 from that of the young M. bonariensis : the cry of the latter is a long, 

 shrill, two-syllabled note, the last syllable being prolonged into a con- 

 tinuous squeal when the foster-parent approaches with food ; the cry of 

 the young M. badius is short, reedy, tremulous, and uninflected. The 

 resemblance of the young M. rufoaxillaris to its foster-brothers in 

 language and plumage is the more remarkable when we reflect that 

 the adult bird in its habits, gestures, guttural notes, also in its deep 



