222 DARWINISM 



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 

 flight. 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, 



