in contrast to the black body, screams and gyrates, and then instantly returns to his former post and resumes his erect pose of waiting. It is hard to imagine a more conspicuous bird than the silver-bill; but the next and last tyrant flycatcher of which I shall speak possesses on the whole the most advertising coloration of any small bird I have ever seen in the open country, and moreover this advertising coloration exists in both sexes and throughout the year. It is a brilliant white, all over, except the long wing-quills and the ends of the tail-feathers, which are black. The first one I saw, at a very long distance, I thought must be an albino. It perches on the top of a bush or tree watching for its prey, and it shines in the sun like a silver mirror. Every hawk, cat, or man must see it; no one can help seeing it.
These common Argentine birds, most of them of the open country, and all of them with a strikingly advertising coloration, are interesting because of their beauty and their habits. They are also interesting because they offer such illuminating examples of the truth that many of the most common and successful birds not merely lack a concealing coloration, but possess a coloration which is in the highest degree revealing. The coloration and the habits of most of these birds are such that every hawk or other foe that can see at all must have its attention attracted to them. Evidently in their cases neither the coloration nor any habit of concealment based on the coloration is a survival factor, and this although they live in a land teeming with bird-eating hawks. Among the higher vertebrates there are many known factors which have influence, some in one set of cases, some in
