1863.] MR. A. R. WALLACE ON THE BIRDS OF BOURU. 2/ 



parted from the usual gay colouring of its allies, and is actually the 

 dullest-coloured of its family, while the Honeysucker very much 

 resembles in its coloration other species of the group to which it 

 belongs. The imitation is carried to the minutest particulars : the 

 bare black orbits of the Trojndorhynchus are copied by a patch of 

 dusky feathers in the Mimeta ; the rigid lanceolate feathers on the 

 head of the former are imitated by dark stripes on the broader fea- 

 thers of the latter ; and even the very peculiar ruff of recurved fea- 

 thers on the nape of the Tropidorhynchus has its general effect imi- 

 tated by a collar of a pale colour in the Mimeta. The under and 

 upper surfaces of the two birds are as near as possible of the same 

 tint respectively ; and, stranger still, the Oriole has closely copied the 

 mode of flight and the voice of its model ; so that in a state of nature 

 the two birds are practically undistinguishable. Most of the species 

 of Tropidorhynchus have an elevated keel or protuberance at the 

 base of the bill. In the Bouru bird this is altogether wanting ; yet 

 in the Mimeta which copies it there is a slight protuberance at the 

 base of the bill, which does not occur in any other species of its 

 genus — almost making us think that some ancestors of the present 

 bird had mimicked a species of Tropidorhynchus which possessed the 

 protuberance, and that their descendant, finding himself in the com- 

 pany of a bird without this ornament, was gradually losing it, but 

 had not yet quite done so. It has been observed by Mr. Bates, and 

 is no doubt generally true, that mimicking species are much less 

 abundant than those they copy. In the present instance it seems to 

 be different ; for I obtained many specimens of the Mimeta before I 

 saw a single Tropidorynchus, though in other islands the latter was 

 generally the most abundant. Perhaps in this case it has carried 

 the imitation to such an extent as actually to gain an advantage over 

 its model in the struggle for existence. This curious instance of 

 mimicry does not stand alone ; for in the adjacent island of Ceram, 

 two allied but very distinct species {Mimeta forsteni and Tropido- 

 rhynchus subcornutus) resemble each other with equal accuracy. 

 What peculiar immunity from danger the Tropidorhynchi possess, 

 which makes it advantageous for other birds to imitate them, it is 

 not very easy to see. In the case of insects, it seems probable that 

 it is the odour or taste of the imitated species which is unpalatable 

 to insect-eating birds ; or, in other cases, like the clear-winged Moths 

 which mimic Hymenoptera, the mimicked species are armed with a 

 sting. In birds it is evident that the bravest, strongest, and best- 

 armed groups should be the subjects of mimicry, and the weakest 

 and most defenceless those which obtain some advantage by imita- 

 ting them. Now this is certainly the case, for the Raptores are the 

 most frequent subjects of imitation — a Parrot {Strigops) imitating an 

 Owl, some Curassows of the genus Ibycter resembling Hawks (Ibis, 

 vol. ii. p. 223), and Cuckoos frequently resembling Hawks. A 

 species was named by Temmiuck Falco cuculoides ; and in all parts 

 of the world the larger grey and banded Cuckoos are mistaken by 

 the natives for Hawks. Cuckoos, however, which are certainly 

 among the weakest and most defenceless of birds, imitate several 



