Sight and hearing are highly developed in birds, and the senses, besides
pulling the triggers of inborn efficiencies, supply the raw materials
for intelligence. There is some truth, though not the whole truth, in
the old philosophical dictum, that there is nothing in the intellect
which was not previously in the senses. Many people have admired the
certainty and alacrity with which gulls pick up a fragment of biscuit
from the white wake of a steamer, and the incident is characteristic. In
their power of rapidly altering the focus of the eye, birds are
unsurpassed.
To the sense of sight in birds, the sense of hearing comes a good
second. A twig breaks under our feet, and out sounds the danger-call of
the bird we were trying to watch. Many young birds, like partridges,
respond when two or three hours old to the anxious warning note of the
parents, and squat motionless on the ground, though other sounds, such
as the excited clucking of a foster-mother hen, leave them indifferent.
They do not know what they are doing when they squat; they are obeying
the living hand of the past which is within them. Their behaviour is
instinctive. But the present point is the discriminating quality of the
sense of hearing; and that is corroborated by the singing of birds.
It is emotional art, expressing feelings in the medium of sound. On the
part of the females, who are supposed to listen, it betokens a
cultivated ear.
[Illustration: THE BEAVER
The beaver will gnaw through trees a foot in diameter; to save itself
more trouble than is necessary, it will stop when it has gnawed the
trunk till there is only a narrow core left, having the wit to know that
the autumn gales will do the rest.]
[Illustration: _Photo: F. R. Hinkins & Son._