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 { ix} 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.