INTEODUCTION. 



xv 



not necessarily mean insulation, as some writers appear to assume. Wallace puts it very clearly : 

 ' Isolation will often be produced in a continuous area whenever a species becomes modified 

 in accordance with varied conditions or diverging habits. For example, a wide-ranging species 

 may, in the northern or colder part of its area, become modified in one direction, and in the 

 southern part in another direction ; and, though for a long time an intermediate form may 

 continue to exist in the intervening area, this will be likely soon to die out, both because its 

 numbers will be small, and it will be more or less pressed upon in varying seasons by the modified 

 varieties, each better able to endure extremes of climate. So, when one portion of a terrestrial 

 species takes to a more arboreal or to a more aquatic mode of life, the change of habit itself leads 

 to the isolation of each portion." 



Now, it is not difficult to imagine that in the case of a country which was gradually 

 emerging from the depths of the ocean, presenting for long-continued periods of time low flats 

 more or less covered with scrubby vegetation, available for purposes of concealment, a smaller 

 size would be beneficial to the already practically wingless birds, the more so if correlated with a 

 longer bill, for the purpose of hunting for annelids and insects in the increasing deposits of 

 mould covering these newly-formed flats. And, bearing in mind that natural selection acts 

 solely " by the preservation of useful variations, or those which are beneficial to the organism 

 under the conditions to which it is exposed," we should in this case regard the so-called 

 degeneration of the Kiwi as an improvement in the organism of the bird in relation to its 

 conditions and environment. So also, in regard to those wingless birds which continued to 

 inhabit the table-lands, and to subsist on fern-roots and the ever-present "cabbage-tree," should 

 we regard a longer neck and a stronger bill as beneficial variations, especially if correlated with a 

 more massive posterior development, such as that which distinguishes Dinomis elephantopus and 

 Dinomis crassus. May not the " giant Kiwi " (Megalapteryx hectori), the remains of which were 

 discovered and described by the late Sir Julius von Haast, represent one of the intermediate forms 

 which have been stamped out and lost in the long-continued struggle for existence along the 

 borderland, so to speak, of these different races of wingless birds ? 



As I have already stated, each so-called species of Kiwi is restricted in its range to a 

 particular district. In the case of all the species this range is insular, save as to the appear- 

 ance of the grey Kiwi on the Tararua range, which I shall presently endeavour to account for. 

 Now, if any sudden catastrophe were to overtake New Zealand, destroying all animal life, 

 the remains of the different species of Kiwi (so far as they could be distinguished) would 

 be found in different localities and never commingled. This is not the case with Dinomis 

 and its allies. The bones of about a thousand birds were exhumed by Sir Julius von Haast 

 from the Glenmark marshes, and these comprised the skeletons of several genera and numerous 

 species, varying considerably in stature, all mixed up indiscriminately together, showing 

 that these birds had inhabited the plains of Canterbury at one and the same time. I have 

 endeavoured to furnish an explanation of this in my introduction to the 'Birds of New 

 Zealand,' pages xxxiv. and xxxv. Adopting a theory first put forward by Professor Hutton — to 

 whom I acknowledge my indebtedness — I attempted to show how this could have been brought 

 about by natural causes. By going much further back in time — and that is the charm of 

 the evolution theory, that it imposes practically no limits as to time and space — I have supposed 

 that in very ancient times two or more species of brevipennate birds, themselves the descendants 

 of volant birds of a still earlier epoch, roamed over a great southern continent, which, by some 

 convulsion of nature, was afterwards submerged, leaving its higher levels and mountain-tops 

 exposed in the form of numerous scattered islands, on which the survivors of the wingless race of 

 birds would naturally remain ; that this state of things continued long enough — how long it is 



