deterrent quality, and that its bright colours are due to at present unknown causes, and serve unknown purposes.
Some brightly coloured animals have no warning colour or other protection, but trust to their own intelligence to avoid danger. Thus "the bright colour of the male Golden Oriole renders it peculiarly liable to be attacked by the Sparrowhawk, and in such a contingency the Oriole does not trust to his Thrush-like flight enabling him to elude his tormentor in the open, but on the earliest opportunity seeks refuge in the densest thicket available as cover."[1] The Rose-coloured Pastor, with the back, breast, and sides of an exquisite pale pink, is observed in its continental haunts to frequent trees or shrubs bearing rose-coloured flowers, such as the blossoms of the pink azalea, among which the birds more easily escape notice.[2]
Many plants owe their protection from the ravages of grazing animals to offensive odours, which to ourselves are unappreciable while the leaves are intact, and these apparently possess no warning colours, or, at all events, none of those glaring hues on which the theory is founded. These, however, are avoided by the animals from whom protection is required, and who have either learned to distinguish the plants by their appearance, or have a greater delicacy of smell than ourselves. Grazing animals also avoid plants furnished with stinging hairs, which certainly seems due to observation, and probably inherited experience. The European nettles (Urtica dioica and U. urens) are generally left alone, and how much more so the U. stimulans of Java, the U. crenulata of India, and U. mentissima of Timor, whose stinging hairs are capable of producing severe attacks of tetanus as by snake-bites.[3] These plants, however, seem to have developed no prominent warning colours as understood by the theory; while their protection is undoubtedly real and efficient. The theory of warning colours is a brilliant suggestion, but one which seems to demand of nature an unnecessary effort to supplement protective qualities already sufficient. The argument has been thoroughly advanced by Prof. Poulton, who
