Hawks and Hawking. 31 



to living entirely on small mammals and birds. In such a case, 

 if the competition with other birds leading a similar mode of 

 life were severe, any slight modification of form, amongst the 

 offspring of such shrikes as would enable the younger generation 

 to compete successfully with their fellow-birds in the struggle 

 for existence, would be a manifest advantage to the possessor, 

 and would enable that bird to hold its own while others around 

 it would be di'iven out of the field. Such beneficial modification 

 of form would, of necessity, lead by slow degrees to the assump- 

 tion of the external characteristics of the birds of prey, for the 

 simple reason that those external characteristics are just such 

 as best suit the mode of life of the possessor. Taking the case 

 of the same birds, again, we find many of them, the common 

 barn-door fowl for example, and the currasows especially, feeding 

 occasionally upon small mammals or birds. The currasows at 

 the Zoological Gardens will catch and kill and eat a mouse in 

 almost as systematic a manner as the Kestrel does ; and the 

 same may be said of many allied forms. It is quite conceivable 

 that, imder changed conditions of their normal surroundings, 

 the currasows might be compelled to subsist entirely on small 

 mammals or birds of their own catching, and in this case such 

 of then- descendants as developed characteristics better fitting 

 them for their raptorial mode of hfe would be more likely to 

 survive and to leave numerous descendants than the birds that 

 did not vary in that direction from the parental form. The case 

 of the currasows is especially interesting, because in many of 

 their structural characteristics they closely approach some of the 

 aberrant iEtomorphs — the Polyborines and the allied forms, for 

 example. Then, again, there is the case of the now well-known 

 carnivorous parrot, which has made quite a new start in life 

 within the last fifty years, and given up a diet of fern-roots for 

 a more substantial one of mutton. No one can for a moment 

 doubt that, if its former diet failed, this particular form of parrot 

 could soon pick up a living by preying upon other denizens of 

 that part of the world ; and even if deprived of sheep-flesh it 

 could supply_its need just as adroitly by attacking other animals 

 as it does now with the colonist's sheep. In course of time, 

 unless external circumstances intervened to prevent it, Natural 

 Selection would develop a bird that might still retain some of 

 the internal structural characteristics of the Parrots, and yet be, 

 externally, and in all essential points in its habits, a veritable 

 bird of prey. No one, again, who will study the appearance 

 and the habits of the remarkable Cuvier's Fodan/us, now (1885) 

 living in the Zoological Gardens, can doubt that this very owl- 

 like bird represents either one of two things : it is either a com- 

 paratively unmodified descendant of the common ancestors of 

 the owls and goatsuckers, or else it is a raptorial type developed 



