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06 - Difficutiles in Theory 06-05 - Diversified Habits in the Same Species 10 I will now give two or three instances both of diversified and of changed habits in the individuals of the same species.

In either case it would be easy for natural selection to adapt the structure of the animal to its changed habits, or exclusively to one of its several habits.

It is, however, difficult to decide, and immaterial for us, whether habits generally change first and structure afterwards; or whether slight modifications of structure lead to changed habits; both probably often occurring almost simultaneously.

Of cases of changed habits it will suffice merely to allude to that of the many British insects which now feed on exotic plants, or exclusively on artificial substances.

England
England

insect
insect


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 into it like a kingfisher at a fish.

Tyrant Flycatcher
Tyrant Flycatcher

South America
South America

kestrel
kestrel

kingfisher
kingfisher


In our own country the larger titmouse (Parus major) may be seen climbing branches, almost like a creeper; it sometimes, 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.
England
England

titmouse
titmouse

seeds
seeds

yew
yew


In North America the black bear was seen by Hearne swimming for hours with widely open mouth, thus catching, almost like a whale, insects in the water.

bear
bear
whale
whale
06 - Difficutiles in Theory 06-05 - Diversified Habits in the Same Species 20 As we sometimes see individuals following habits different from those proper to their species and to the other species of the same genus, we might expect that such individuals would occasionally give rise to new species, having anomalous habits, and with their structure either slightly or considerably modified from that of their type. And such instances occur in nature.

Can a more striking instance of adaptation be given than that of a woodpecker for climbing trees and 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.
North America
North America

woodpecker
woodpecker

fruit
fruit

insect
insect


On the plains of La Plata, where hardly a tree grows, there is a woodpecker (Colaptes campestris) which has two toes before and two behind, a long pointed tongue, pointed tail-feathers, sufficiently stiff to support the bird in a vertical position on a post, but not so stiff as in the typical woodpeckers, and a straight strong beak.

La Plata
La Plata

Colaptes Campestris
Colaptes Campestris


The beak, however, is not so straight or so strong as in the typical woodpeckers, but it is strong enough to bore into wood.

Hence this Colaptes in all the essential parts of its structure is a woodpecker.

Even in such trifling characters as the colouring, the harsh tone of the voice, and undulatory flight, its close blood-relationship to our common woodpecker is plainly declared; yet, as I can assert, not only from my own observation, but from those of the accurate Azara, in certain large districts it does not climb trees, and it makes its nest in holes in banks!

In certain other districts, however, this same woodpecker, as Mr. Hudson states, frequents trees, and bores holes in the trunk for its nest. I may mention as another illustration of the varied habits of this genus, that a Mexican Colaptes has been described by De Saussure as boring holes into hard wood in order to lay up a store of acorns.
Mexican Jay
Mexican Jay

acorn
acorn