no BIRDS OF LA PLATA 



crease in another more favoured species over the 

 same region. It is not as if the regnant species had 

 invaded and seized on the province of another, but 

 appears rather as if they had quietly entered on the 

 possession of an inheritance that was theirs by right. 

 Mighty as are the results worked out by such a 

 process, it is only by a somewhat strained metaphor 

 that it can be called a struggle. But even when the 

 war is open and declared, as between a raptorial 

 species and its victims, the former is manifestly 

 driven by necessity, and in this case the species 

 preyed on are endowed with peculiar sagacity to 

 escape its persecutions ; so that the war is not one 

 of extermination, but, as in a border war, the invader 

 is satisfied with carrying off the weak and unwary 

 stragglers. Thus the open declared enmity is in 

 reality beneficial to a species ; for it is sure to cut 

 off all such individuals as might cause its degenera- 

 tion. But we can conceive no necessity for such a 

 fatal instinct as that of the Cuckoo and Cow-bird, 

 destructive to such myriads of lives in their begin- 

 ning. And inasmuch as their preservation is inimical 

 to the species on which they are parasitical, there 

 must also here be a struggle. But what kind of 

 struggle i not as in other species, where one perishes 

 in the combat that gives greater strength to the 

 victor, but an anomalous struggle in which one of 

 the combatants has made his adversary turn his 

 weapons against himself, and so seems to have an 

 infinite advantage. It is impossible for him to suffer 

 defeat ; and yet, to follow out the metaphor, he has 



