The Start 37 



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 more- 

 over 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 advertis- 

 ing 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 con- 

 cealing 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 



