In several instances I have treated of extinct flightless species under genera including existing species capable of flight. This may appear to be inconsistent, seeing that I maintain Notornis separate from Porphyrio, but, while not considering flightlessness in itself a generic character, the great development of the wing-coverts and the modification of the toes appear of sufficient generic value in this case. I know that several of the most eminent ornithologists of the day, among them Dr. Sharpe, differ from me, and are convinced that the loss of the power of flight is so profound a modification, that it is imperative that we should treat it as sufficient for generic distinction.
While agreeing that many genera are founded on much less striking modifications, I cannot concur in this opinion, for, unless the loss of the power of flight is also accompanied by other changes, in some cases it is difficult to find at first sight even specific differences other than the aborted wings.
The cause of recent extinction among birds is in most cases due directly or indirectly to man, but we also have instances of birds becoming extinct for no apparent reason whatever.
Man has destroyed, and is continually destroying species directly, either for
food or for sport, but also in many other ways he contributes to their destruction. Some species have been exterminated by the introduction of animals of prey, such as rats, cats, mongoose, etc., and we know that also the acclimatisation of other birds, such as the mynah, etc., has proved to be harmful to the native birds. Again we find that the introduction of domestic creatures or others kept as pets has brought diseases which may prove fatal to the indigenous fauna. Another means by which man causes immense destruction, is by destroying the natural habitat of various species. By cutting down or burning the forests, prairies, or scrub, and by bringing the land under cultivation, man indirectly kills off a species through starvation, from extermination of certain insects or plants on which it depends for food. Many species, such as the Moas, were evidently greatly reduced in numbers by cataclysms of Nature, such as volcanic outbreaks, earthquakes, floods, bush fires, etc., and then died out from what appears only explicable by the natural exhaustion of their vitality. The chief cause of the extermination of the Moas was undoubtedly their slaughter by the Maoris for food, but in several inaccessible parts of the interior large numbers of Moa remains have been found which undoubtedly had died for no apparent reason.
This cause also seems to be the only explanation of the dying out of such birds as Aechmorhynchus, Chaetoptila, Camptolaimus and others.
The melancholy fact however remains that man and his satellites, cats, rats, dogs, and pigs are the worst and in fact the only important agents of destruction of the native avifaunas wherever they go.
I have not included in the body of this work the fossil species from the pleistocene of Europe, Asia, Australia and America, as I believe that these belonged to an avifauna of an epoch considerably anterior to those attributed to the pleistocene of New Zealand and the adjacent islands, as well as that of the Mascarenes and Madagascar. I, however, give here the list of the species described from the above mentioned regions which I have been able to find in our literature, to serve as a guide to those who may think I ought to have included them in the work itself.
"The distal extremity of the tibio-tarsus is narrow, without a semilunar pit on the lateral surface of the ectocondyle, and with a very deep extensor groove" (Lydekker, Cat. Fossil B. Brit. Mus., p. 353).