m 



INTKODUCTION. 



xli 



certainly two phases of the dark plumage— the one uniform slaty-grey, the other paler grey with 

 whitish cheeks and throat— but these differences are in my opinion attributable to age and sex. 



In addition to " dichromatism " there is what is termed " trichromatism," where, apart from 

 the normal form, there are two different colour-phases, although this phenomenon appears to 

 want confirmation, the evidence in support of it being incomplete. If the theory be true, it may 

 help to explain the formation of new species,— the original stock dying out in the struggle for 

 existence, and the dichromatic phases becoming stereotyped into two invariable forms or species, 

 separated geographically, but still identical in structure. Dr. Kingsley mentions an example 

 brought forward by Mr. Eidgway, that of the Scarlet and the White Ibises (Guam rubra and 

 G. alba), of which he remarks that they are now so different in colour that probably no one 

 would deny their specific distinction, though structurally so alike that a specimen of the white 

 one dyed scarlet would be indistinguishable from G. rubra ; and he concludes with this observa- 

 tion : " The question which finally impresses itself upon the inquirer, in view of the above facts, 

 is this : Are not the two or three phases of dichromatic or trichromatic species ' incipient species," 

 the final state of which will be that of the White and the Scarlet Ibises ? The subject is one of 

 the most perplexing, and consequently most interesting, questions in modern ornithology. It 

 shows what we know, and particularly what we do not know ; it shows that ornithology means 

 more than a mere description and naming of birds ; that one of its aims is to contribute to the 

 solution of the great problem of the age—' the origin of species.' " 



Of true xanthochroism— where the plumage is yellow instead of green— I have recorded 

 several beautiful examples, notably a gorgeous yellow Kakapo and a canary-coloured Kea 

 which will be found fully described in vol. ii. of this Supplement. The other instances are 

 among the green F&YYakeets—Cyanorhamphus novce-zealandice, C. auriceps, and C. erythrotis— 

 and the unique yellow Bell-bird in my son's collection. As Prof. Newton has pointed out, this 

 may be a reversionary step, or a case of arrested development, because of the absence of the green- 

 making superstructure.* Of cyanism, the only almost perfect instance I can recall is that of 

 a striking example of Gyanorhamphus novce-zealandice. The late Mr. O. E. Gray's so-called 

 Stri?igops greiji is, without doubt, a case of partial cyanism or of a tendency in that direction. 

 Of erythrism I have obtained very perfect representatives in Nestor meridionalis and Gyano- 

 rhamphus novce-zealandice, the entire plumage being of a brilliant red. 



Whatever the immediate cause of these departures from the normal plumage, the general 

 result is the production of a very conspicuous and beautiful bird. These "freaks" have no 

 intrinsic scientific value ; but it will be seen how much they are sought after by collectors when I 

 mention that the lovely yellow Parrakeet described by Mr. Kingsley! fetched £40, and is now in 

 a museum in this country ; that a black King Penguin, from Macquarie Island, was sold by 

 a dealer for £75 ; and that the price finally placed by the owner on the yellow Kakapo mentioned 

 above was £200 ! 



* My son Percy, who is a keen entomologist, in the last letter I received from him (dated Wellington, 17th 

 December, 1904) writes : " There is a remarkable illustration of xanthochroism among the large Green Moths (Hepialus 

 virescens) in this country. I have made a great haul of these lately, capturing as many as thirteen absolutely perfect 

 specimens in a single evening. One of these was of a uniform bright orange. A bright yellow ' Green Moth ' is as 

 great a rarity among Lepidoptera as a yellow Kakapo among birds, and the phenomenon is probably due to the same 

 cause in both cases. At Papaitonga they emerge, about 9 o'clock in the evening, from the thick stems of Aristotelia 

 racemosa, and are easily taken in a net as they wheel round a suspended lantern, emitting a bright light." 



t Trans. N. Z. Inst., vol. xxiii., p. 192. 



/ 



