Through the Brazilian ii'ildcnicss. 
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 shijies 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 
colouration, are interesting because of their beauty and habits. 
They are also interesting because they offer such illuminating- 
examples of the truth that many of the most common and suc- 
cessful birds not merely lack a concealing colouration, but 
possess a colouration which is in the highest degree revealing. 
The colouration 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 colouration nor any habit of concealment based on the 
colouration is a survival factor, and this although they live in a 
land teeming with bird-eating hawks .... Courage, 
intelligence, adaptibility, prowess, bodily vigour, speed, alert- 
ness, ability to hide, ability to build structures which will 
protect the young while they are helpless, fecundity — all, and 
n^'iny more like thfui. h;i\e their several places: and behind all 
these visiljle 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 everyone of the 
attributes above enumerated is a survival factor in some species, 
while in others it lias no survival value at all, 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 existed 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 llie death of countless other species of 
far greater intelligence, but in other ways less ada])ted to succeed 
in environmental complex. The same statement can be made of 
all the many, many other known factors in development, from 
fecundity to concealing colouration; and l)ehind these lie forces 
