, 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.
Courage, intelligence, adaptability, prowess, bodily vigor, speed,
alertness, ability to hide, ability to build structures which will
protect the young while they are helpless, fecundity--all, and many
more like them, have their several places; and behind all these
visible causes there are at work other and often more potent causes of
which as yet science can say nothing. Some species owe much to a given
attribute which may be wholly lacking in influence on other species;
and every one of the attributes above enumerated is a survival factor
in some species, while in others it has no survival value whatever,
and in yet others, although of benefit, it is not of sufficient
benefit to offset the benefit conferred on foes or rivals by totally
different attributes. Intelligence, for instance, is of course a
survival factor; but to-day there exist multitudes of animals with
very little intelligence which have persisted through immense periods
of geologic time either unchanged or else without any change in the
direction of increased intelligence; and during their species-life
they have witnessed the death of countless other species of far
greater intelligence but in