advertises him for a quarter of a mile round about. But every few
minutes he springs up into the air to the height of twenty or thirty
feet, the white wings flashing 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
another set of cases, in the development and preservation of species.