NATURAL SELECTION AS APPLIED TO BIRDS 331 



Island of Celebes closely resembles the inoffensive Honey- 

 buzzard {Pernis celebensis) of the same island, and this in both 

 its immature and adult plumages. 



Similarly, the South American Caracara or Curassow-hawk 

 {Ibycter americanus) bears a wonderful resemblance to one of 

 the Game-birds of the same region — a Curassow of the Genus 

 Ortalis. Now the Caracara is primarily a Carrion-hawk, but will 

 eat small^ birds whenever he can get them — which is generally 

 by stealth. Like the Curassow, which he so closely resembles, 

 he sits motionless for hours in a tree, and thinking no evil of a 

 Curassow, small birds come and perch beside him, when they 

 are seized before they can realise the mistake they have made ! 



No one supposes, of course, that these instances of mimicry 

 in any way imply a conscious mimicry. Nor is it likely that 

 they are the outcome of a process of selection whereby the in- 

 dividuals concerned assumed, by slow degrees, their ultimate 

 likeness one to another, a likeness which has been built up out 

 of strikingly unlike material. The case of the Oriole and the 

 Friar-bird, for example, is not to be regarded as an instance of 

 a brilliantly coloured bird, such as Orioles usually are, becoming 

 slowly transformed into one of sombre hues. For it must be 

 remembered that in its immature dress the brightest Oriole is 

 dull. Rather we must suppose that these mimicking Orioles 

 have survived side by side with their models the Friar-bird, be- 

 cause they had not inherited the tendency to develop the bright 

 colours which characterise their relatives in other lands. We 

 must regard them, in short, as representing rather the more 

 primitive stock from which the brightly coloured species were 

 evolved. Any individuals which did tend to develop colour 

 would have been weeded out through the persecution which 

 these congenitally duller brethren escape. 



The facts so far submitted have been selected with a view 

 to demonstrating the factors which determine the avi-fauna of 

 any given area, and the factors which govern the coloration 

 and shapes of the individuals of that avi-fauna. 



That inter-specific selection is a fact there is scarcely room 

 for doubt. And the reality of intra-specific selection — the 

 struggle between individuals of the same species — should be no 

 less apparent. 



The importance of the latter in the matter of the evolution 



