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Show 262 DARWINISM CHAI'. harmless Homalocranium semicinctum ; and Elaps ~em~iscatus in Brazil is copied by Oxyrhopus trigeminus ; while m other parts of South America si~ilar_ c~ses. of mimicry occur, sometimes two harmless species 1m1tatmg the same poisonous snake. A few other instances of mimicry in this group have been recorded. There is in South Africa an egg-eating snake (Dasypeltis scaber), which has neither fangs nor teeth, yet it is very like the Berg adder (Olothos atrop~s), and ':hen alarmed renders itself still more like by flattenmg out 1ts head and dartino· forward with a hiss as if to strike a foe.1 Dr. A. B. Meyer0 has also discovered that, while . ~me species of . the genus Oallophis (belonging to the same fa~ruly as the Amencan Elaps) have laro·e poison fangs, other specie of the same o-enns have none; and that' one of the latter (0. gracili ) resembles a poisonous species (0. intestinalis) so closely, that only an exact comparison will discover the difference of colour an<l marking. A similar kind of resemblance is said to exist between another ha,rmless snake, Megrerophis flaviceps, awl the poisonous Oallophis bivirgatus; and in both these c;uw-; the harmless snake is less abundant than the poisonous o1w. as occurs in all examples of true mimicry. 2 In the genus Elaps, above referred to, the very peculiar style of colour and marking is evidently a "warning colour " for the purpose of indicating to snake-eating birds and mammals that these species are poisonous; and this throws light on the long-disputed question of the use of the rattle of the rattlesnake. This reptile is really both sluggish and timid, and is very easily captured by tr.ose who know its habits. If gently tapped on the head with a stick, it will coil itself up and lie still, only raising its tail and rattling. It may tlwn be easily caught. This shows that the rattle is a warning to its enemies that it is dangerous to proceed to extremi tic::;; and the creature has probably acquired this structure and habit because it frequents open , or rocky districts where protective colour is needful to save it from being pounced upon by buzzards or other snake-eaters. Quite parall el in function is the expanded hood of the Indian cobra, a 1 Natnre, vol. xxxiv. p. 547. 2 Proceedings of the Zool. Soc. of London, 1870, p. 369. IX WARNING COLORATION AND MIMICRY 263 poisonous snake which belongs also to the Elapidre. This is, no donht, a warning to its foes, not an attempt to terrify it. prey ; and the hood has been acquired, as in the case of the ra,ttlesnake, because, protective coloration being on the whole useful, some mark was required to distinguish it from other protectively coloured, but harmless, snakes. Both these species feed on active creatures capable of escaping if their enemy were visible at a moderate distance. Mimic1·y among Birds. The varied forms and habits of birds do not favour the production among them of the phenomena of warning colours or of mimicry ; and the extreme development of their instincts and reasoning power., as well as their activity and their power of flight, usually afford them other means of evading their enemies. Yet there are a few imperfect, n.nd one or two very perfect cases of true mimicry to be found among them. The less perfect examples are those presented by severaJ species of cuckoos, an exceedingly weak and defenceless group of birds. Our own cuckoo is, in colour and markings, very like a sparrow -hawk In the East, several Qf the small black cuckoos closely resemble the aggressive drongo-shrike of the same country, and the small metallic cuckoos are like glossy starlings; while a large groundcuckoo of Borneo (Oarpococcyx radiatus) resembles one of the fine pheasants (Euplocamus) of the same country, both in form and in its rich metallic colours. More perfect cases of mimicry occur between some of the dull-coloured orioles in the Malay Archipelago and a genus of large honey-suckers-the Tropidorhynchi or "Friar-birds." These latter are powerful and noisy birds which go in small flocks. They have long, curved, and sharp beaks, and powerful grasping claws; and they are quite able to defend themselves, often driving away crows and hawks which venture to approach them too nearly. The orioles, on the other hand, are weak and timid birds, and trust chiefly to concealment and to their retiring habits to escape persecution. In each Qf the great islands of the Austro-Malayan region there is a distinct species of Tropidorhynchus, and there is always along with it an oriole that exactly mimics it. All the Tropidorhynchi |
