222 
DARWINISM 
CHAP. 
Among birds, these recognition marks are especially 
numerous and suggestive. Species which inhabit open 
districts are usually protectively coloured ; but they generally 
possess some distinctive markings for the purpose of being 
easily recognised by their kind, both when at rest and during 
Right. Such are, the white bands or patches on the breast 
or belly of many birds, but more especially the head and 
neck markings in the form of white or black caps, collars, 
eye-marks or frontal patches, examples of which are seen in 
the three species of African plovers figured on page 221. 
Recognition marks during flight are very important for all 
birds which congregate in flocks or which migrate together; 
and it is essential that, while being as conspicuous as possible, 
the marks shall not interfere with the general protective tints 
of the species when at rest. Hence they usually consist of 
well-contrasted markings on the wings and tail, which are 
concealed during repose but become fully visible when the 
bird takes flight. Such markings are well seen in our four 
British species of shrikes, each having quite different white 
marks on the expanded wings and on the tail feathers; and 
the same is the case with our three species of Saxicola—the 
stone-chat, whin-chat, and wheat-ear—which are thus easily 
recognisable on the wing, especially when seen from above, as 
they would be by stragglers looking out for their companions. 
The figures opposite, of the wings of two African species 
of stone-curlew which are sometimes found in the same 
districts, well illustrates these specific recognition marks. 
Though not very greatly different to our eyes, they are no 
doubt amply so to the sharp vision of the birds themselves. 
Besides the white patches on the primaries here shown, the 
secondary feathers are, in some cases, so coloured as to afford 
very distinctive markings during flight, as seen in the central 
secondary quills of two African coursers (Fig. 21). 
Most characteristic of all, however, are the varied markings 
of the outer tail-feathers, whose purpose is so well shown by 
their being almost always covered during repose by the two 
middle feathers, which are themselves quite unmarked and 
protectively tinted like the rest of the upper surface of the 
body. The figures of the expanded tails of two species of East 
Asiatic snipe, whose geographical ranges overlap each other, 
