II PROTECTIVE RESEMBLANCES AMONG ANIMALS 75 
has a very scaly appearance, being covered with rigid pointed 
feathers which are not imitated in the Mimeta, although there 
are signs of faint dusky spots which may easily furnish the 
groundwork of a more exact imitation by the continued 
survival of favourable variations in the same direction. 
There is also a large knob at the base of the bill of the 
Tropidorhynchus which is not at all imitated by the Mimeta. 
In the island of Morty (north of Gilolo) there exists the 
Tropidorhynchus fuscicapillus, of a dark sooty brown colour, 
especially on the head, while the under parts are rather 
lighter, and the characteristic ruff of the nape is wanting. 
Now it is curious that in the adjacent island of Gilolo should 
be found the Mimeta pheochromus, the upper surface of 
which is of exactly the same dark sooty tint as the Tropido- 
rhynchus, and is the only known species that is of such a dark 
colour. The under side is not quite light enough, but it is a 
good approximation. This Mimeta is a rare bird, and may 
very probably exist in Morty, though not yet found there ; 
or, on the other hand, recent changes in physical geography 
may have led to the restriction of the Tropidorhynchus to 
that island, where it is very common. 
Here, then, we have two cases of perfect mimicry and two 
others of good approximation, occurring between species of 
the same two genera of birds; and in three of these cases the 
pairs that resemble each other are found together in the same 
island, and to which they are peculiar. In all these cases the 
Tropidorhynchus is rather larger than the Mimeta, but the 
difference is not beyond the limits of variation in species, and 
the two genera are somewhat alike in form and proportion. 
There are, no doubt, some special enemies by which many 
small birds are attacked, but which are afraid of the Tropido- 
rhynchus (probably some of the hawks), and thus it becomes 
advantageous for the weak Mimeta to resemble the strong, 
pugnacious, noisy, and very abundant Tropidorhynchus. 
My friend, Mr. Osbert Salvin, has given me another in- 
teresting case of bird mimicry. In the neighbourhood of Rio 
Janeiro is found an insect-eating hawk (Harpagus diodon), 
and in the same district a bird-eating hawk (Accipiter pileatus) 
which closely resembles it. Both are of the same ashy tint 
beneath, with the thighs and under wing-coverts reddish 
