19--Recognition marks of three African plovers.] 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.