96 HUTTON, Land Birds of New Zealand. [5th Tan 



But when we go into details we come across many anomalies. 

 Petrceca has varied between the two islands, but the South 

 Island species {P. inacrocephala) is unaltered in the Chatham 

 Islands and Auckland Islands. SphencBacus has changed in 

 the South Island, where the two species live together, but 5. 

 fulvus is alone found on the Snares, while 5. rufcsccns is confined 

 to the Chatham Islands. Anthornis has changed in the Chat- 

 ham Islands, but not in the Auckland Islands. On the other 

 hand, Prosthcmadera has not changed on any of the islands. 

 Ocydromus ear It remains the only species in the North Island, 

 but in the South Island it has split up into three or four species. 

 As might have been expected, no good fliers have representative 

 species in the two islands of New Zealand, but Anthornis, Anthus, 

 Cyanorhamphus, Hcmiphaga, and Thinornis are represented by 

 different species in some of the outlying islands. xAlso some 

 badly flying species, such as Sphcnceacus, Pseudogcrygone, Rhip- 

 idura, Acaiithulositta, and Xoiicus, are identical on both islands 

 of New Zealand. Again, some of the Rails, such as Hypotcenidia 

 philippinensis and Porzana tabuensis, remain unchanged; while 

 others, such as Ocydromus and the lately extinct Rails of the 

 Chatham Islands, have varied greatly. Once more, while 

 SphencBacus, Petrceca, Pscudogerygone, and Rhipidura have 

 undergone only specific changes since their ancestors came to 

 New Zealand, the New Zealand members of the ParidcB and the 

 Meliphagidce have changed considerably. But I have said 

 enough to show that not only do different species vary at difterent 

 rates, but that the same species varies at difterent rates in 

 different places. 



New Zealand is well placed for studying the eftects of environ- 

 ment on variation, but it lands us only in puzzles. Certainly 

 there is greater variety of conditions in the South than in the 

 North Island, and the South Island has a larger number of 

 species ; but I find it impossible to connect the difference of 

 conditions with any of the specific changes. Why, for instance, 

 should the species of Ocydromus be darker in the neighbourhood 

 of the West Coast sounds, and lighter in subalpine ranges ? 

 Why should Sphcnceacus get paler in the south ? Or what has 

 the fawn-coloured breast of Xenicus gilviventris to do with living 

 among rocks ? But to take a special example. The green 

 Parrakeets belonging to the genus Cyanorhaniphus , although not 

 confined to New Zealand, have their headquarters there. Now 

 there are three species living together in the South Island, two 

 on Antipodes, two on the Auckland Islands, and one each on the 

 Chatham Islands and Macquarie Island. The Auckland Island 

 birds have not varied in plumage from the original stock in New 

 Zealand, although they must have been isolated for a long time, 

 as the crest of the sternum has undergone a reduction in size. 

 C. unicolor ^ on the Antipodes, has varied considerably, and C. 

 forhesi and C. erythrotis but slightly ; and it is impossible to 

 connect these changes with the surrounding physical conditions. 



