ow feed on exotic plants, or exclusively on
artificial substances. Of diversified habits innumerable instances
could be given: I have often watched a tyrant flycatcher (Saurophagus
sulphuratus) in South America, hovering over one spot and then
proceeding to another, like a kestrel, and at other times standing
stationary on the margin of water, and then dashing like a kingfisher at
a fish. In our own country the larger titmouse (Parus major) may be seen
climbing branches, almost like a creeper; it often, like a shrike, kills
small birds by blows on the head; and I have many times seen and heard
it hammering the seeds of the yew on a branch, and thus breaking them
like a nuthatch. In North America the black bear was seen by Hearne
swimming for hours with widely open mouth, thus catching, like a whale,
insects in the water. Even in so extreme a case as this, if the supply
of insects were constant, and if better adapted competitors did not
already exist in the country, I can see no difficulty in a race of bears
being rendered, by natural selection, more and more aquatic in their
structure and habits, with larger and larger mouths, till a creature was
produced as monstrous as a whale.

As we sometimes see individuals of a species following habits widely
different from those both of their own species and of the other species
of the same genus, we might expect, on my theory, that such individuals
would occasionally have given rise to new species, having anomalous
habits, and with their structure either slightly or considerably
modified from that of their proper type. And such instances do occur in
nature. Can a more striking instance of adaptation be given than that of
a woodpecker for climbing trees and for seizing insects in the chinks of
the bark? Yet in North America there are woodpeckers which feed largely
on fruit, and others with elongated wings which chase insects on the
wing; and on the plains of La Plata, where not a tree grows, there is a
woodpecker, which in every essential part of its organisation, even in
its colouring, in the harsh tone of its voice, and undulatory flight,
told me plainly of its close blood-relationship to our common species;
yet it is a woodpecker which never climbs a tree!

Petrels are the most aerial and oceanic of birds, yet in the quiet
Sounds of Tierra del Fuego, the Puffinuria berardi, in its general
habits, in its astonishing power of diving, its manner of swimming, and
of flying when u