22).
Numbers of species of pigeons, hawks, finches, warblers, ducks, and innumerable other birds possess this class of markings; and they correspond so exactly in general character with those of the mammalia, already described, that we cannot doubt they serve a similar purpose.[86] [Illustration: FIG.

21 .-- Secondary quills.] [Illustration: FIG.

22 .-- Scolopax megala (upper).

S.stenura (lower).] Those birds which are inhabitants of tropical forests, and which need recognition marks that shall be at all times visible among the dense foliage, and not solely or chiefly during flight, have usually small but brilliant patches of colour on the head or neck, often not interfering with the generally protective character of their plumage.

Such are the bright patches of blue, red, or yellow, by which the usually green Eastern barbets are distinguished; and similar bright patches of colour characterise the separate species of small green fruit-doves.