INTEODUCTION. 





xix 



form the single existing specimen — obtained in the Wellington district nearly half a century ago 

 — will be found figured and fully described in vol ii. of this ' Supplement.' 



Now, all the representative forms I have named are accepted by ornithologists in general as 

 good and true species. But take any two of them and compare them carefully. Who can for a 

 moment doubt their common parentage ? — how far back in time, it is not our present purpose to 

 enquire. "Species," "sub-species," and "geographical forms" are now terms in general use 

 among ornithologists, as well as among other specialists, and, as it seems to me, simply for the 

 purpose of indicating the distinctness or otherwise of the lines of demarcation separating one from 

 another in their present stages of development under the slow and invisible, but nevertheless 

 inevitable and sure, processes of that law of evolution which governs the whole Animal Kingdom. 

 When we come to study the matter more closely it often seems well-nigh impossible to draw any 

 specific line at all. So-called species often appear to run into one another by insensible gradations ; 

 so much so, indeed, that no two naturalists are agreed as to how much persistent difference is 

 necessary to constitute a species, as distinguished from a sub-species or variety. Take, by way of 

 illustration, the various forms of Wood-hen (Ocydromus) inhabiting New Zealand. Dr. Bowdler 

 Sharpe, who, as a rule, does not err on the side of "lumping," has declared (Bull. B. 0. C, 1893, 

 p. 30) that he finds it impossible to distinguish Ocydromus greyi of the North Island from 

 Ocydromus earli of the South Island. He says further (loc. cit., p. 29) that he prefers the simple 

 arrangement in my first edition of the 'Birds of New Zealand,' limiting the number of species to 

 three, to that of my second edition, fifteen years later, which admits five species of the group. 

 This alteration, however, was not made by me hastily or without full consideration. I believe 

 I have critically examined a very much larger number of Ocydromi than any other working 

 ornithologist, and, although I do not wish to underrate the perplexities presented by the 

 intergrading of plumage, I think that I have adopted a very cautious rule of admission. Professor 

 Hutton has recognised at least one more form — namely, Ocydromus finschi — and a naturalist given 

 to what is termed "splitting" might easily have increased the number still further. But this 

 is the crux of the whole thing. In this particular instance the species of one naturalist is the 

 "sub-species" of another, and the "local race" of a third. What is this but the existence of 

 transitional forms under the steady march of evolution ? 



But the question of the great variability of the South Island Wood-hens opens up a larger 

 one, which I confess myself quite unable to answer. How is it that in the North Island there is 

 but one well-marked species of Wood-hen spread over its entire area, whilst in the South Island, 

 under practically the same conditions of environment, there are at least four species, and possibly 

 more, merging into one another in such a way as to puzzle even the most expert ornithologists ? 



The genus Ocydromus offers an exceptionally good example for a study of this sort, because, 

 although furnished with ample wings, the quills are soft and useless, and the birds in consequence 

 are flightless. 



To take another instance of the kind : the Kakapo or Ground-parrot (Stringops habroptilus) 

 has ample wings, and yet it is incapable of flight. The presence of this flightless bird, essentially 

 the same in all respects, in both Islands, presents a difficulty which cannot be ignored. Some 

 species are, however, more persistent in their character than others ; and it may be that 

 the Kakapo, as it existed in different areas before the final elevation, had reached its full develop- 

 ment, and has remained stationary ever since. Its markings had become so exactly like the 

 green mosses and other vegetation among which it feeds, thus effectually protecting it from birds 

 of prey, and, in the absence of feral animals, the faculty of flight had become so unnecessary to 

 it, that it is difficult to see in what direction natural selection could operate further to the 

 advantage of the bird. It may be asked why, seeing that the Kakapo is flightless from long 

 disuse of its wings, these members have not been more completely aborted, or dwarfed to mere 



