The little insectivorous Iora (Ægithina tiphia) of India strongly resembles in size and colour a Siskin (Chrysomitris colambiana) from South America, the males in both being black above and yellow below, while in the females the black is replaced by olive-green.
Another Indian babbler (Cephalopyrus flammiceps), yellowish-green, with orange forehead, is closely copied by, or copies, the well-known Brazilian Saffron-finch (Sycalis flaveola).
In Fergusson Island, near New Guinea, there is a ground pigeon (Otidiphaps insularis) which is black with chestnut wings, like several of the powerful ground cuckoos of the genus Centropus, but no species of these cuckoos so coloured appears to inhabit the island.
In Africa there is a tit (Parus leucopterus) which has the same very unusual colouration as an East-Indian bulbul (Micropus melanoleucus), both being black with a white patch on the wing-coverts. These two birds are about the same size. As showing the purely coincidental character of such resemblances, we may mention that this same rare pattern occurs again in our Black Guillemot (Uria grylle) and in the Muscovy Duck (Cairina moschata).
We have already quoted Gadow (p. 198) on “false mimicry” among snakes. He also gives, on p. 110 of Through Southern Mexico, an example of this phenomenon among amphibia. It is, he writes, “impossible to distinguish certain green tree-frogs of the African genus Rappia from a Hyla, unless we cut them open. If they lived side by side, which they do not, this close resemblance would be extolled as an example of mimicry.”
We should be very greatly surprised if abundant examples of “false mimicry” are not found among insects. We trust that this remark will stimulate some entomologist to pay attention to the subject.
It is the essence of Müllerian mimicry that both model and copy are immune from attack from enemies. Unfortunately for the theory, similar resemblances occur among birds of prey, where neither party can benefit from the association. This gives rise to what we may perhaps call false Müllerian mimicry. Thus the goshawk and peregrine falcon resemble each other in being brown above and streaked below in immature plumage, and having barred underparts and a grey upper plumage when adult.
Theory of Mimicry Criticised
Having stated the more important objections to the theory of protective mimicry, it now remains for us to deal specifically with each head of evidence offered in its favour.
1. With regard to the assertion that the model and its copy are often not nearly related, we have shown that among mammals and birds instances of resemblance between widely-separated groups occur under such circumstances that neither party can derive any benefit therefrom.