246 Habit and Instinct. 



parasitical species, there is an extraordinary diversity in 

 the colour, form, and disposition of markings. The 

 embryos and young birds show a remarkable vitality. 

 Mr. Hudson found three eggs which had been built in 

 by the superposition of a new nest on the older one in 

 which they were laid. Their shells were encrusted with 

 dirt and glued together with broken egg-matter spilt over 

 them. Nevertheless one contained a living embryo ready 

 to be hatched, very lively and hungry when he took 

 it in his hand. The young quits the nest as soon as 

 it is able, trying to follow the old bird, and placing itself 

 in the most conspicuous place — such as the summit of a 

 stalk or weed — there demands food with frequent and 

 importunate cries. Thus, one nurse, a little flycatcher, 

 as the only means of standing above its foster-child, had 

 acquired the habit of perching on the back of its charge 

 to feed it. 



Of the other cowbirds of the Argentine, one, the bay- 

 wing (Molothrus hadius), either builds its own nest, a neat 

 and well-built structure, in the fork of a branch, or seizes 

 that of a Lenatero {Anumbius acuticaudatus), and in it, 

 or on it, constructs its own. Several females often lay 

 in the same nest ; but whether the birds pair or practice 

 the promiscuous intercourse common to the genus, Mr. 

 Hudson was unable to discover. 



Very curious are the habits of the other Argentine 

 species, the screaming cowbird {Moluthrus rufoaxillaris). 

 For long they eluded even Mr. Hudson's acute powers of 

 observation. But eventually he was fortunate enough to 

 ascertain that it is parasitic on its cousin, the bay wing. 

 Both the eggs and young of the two species are so similar 

 as to be indistinguishable. The baywing brings up both 

 its own and its cousin's brood, and it is only after some 

 weeks that the difference between the young of the two 



