The Body of a Bird 309 
Hawk must learn to fly still faster. If the duck learns 
to crouch close to the reeds when his flight-feathers are 
moulted and he is helpless, the hawk must develop 
ever sharper eyesight. We may puzzle and puzzle over 
a characteristic habit or a colour of some bird, finding 
no solution, until we discover some special enemy or 
other factor in its life which makes all clear. 
So, among aggressive colours we may mention the 
garb of the penguin, which is steel-gray on the back and 
silvery white below; not to protect it from danger, but 
to enable it the better to approach fish without alarming 
them. It is curious how fish-like the coloration of these 
birds really is, and they are said frequently to lay feet 
and tail together and, drawing their flipper-like wings 
to their sides, spring clear of the water again and again, 
by a single motion of the back muscles, exactly as the 
mammalian dolphins leap ahead of a vessel’s bow. 
Again, while we find the ptarmigan mimicking the 
snow in colour, we find the Arctic Fox, the Snowy Owl, 
and the Gyrfalcon, all of which are enemies of this bird, 
also garbed in white. The ptarmigan may crouch upon 
a drift, but 1t must ever be on the alert, lest from amid 
the snowflakes a white death come suddenly upon it. 
Nature is terribly just in her plan of life’s battles. 
In the same region with these lives the Ivory Gull, 
immaculate as the ice-floe over which it flies, and in its 
whiteness we can perhaps read two purposes: a better 
chance to elude the fierce Gyrfalcon, and a better chance 
to float cloud-like unperceived over the unsuspecting fish 
which it seeks for food. 
