itution the impulse to which I
allude seems to be strongly implanted--the Curlew. When the breeding
season is over, Curlew leave the mountain and the moor and return to
the coast or tidal estuaries for the remainder of the year. Here, at low
water, they find an abundant supply of food--crustaceans amongst the
sea-weed upon the rocks, and lobworms (_Arenicola piscatorum_) in the
mud as the tide advances or recedes. But when the tide is full, they
retire to those parts of the shore that remain uncovered--to isolated
rocks, or to sand-dunes, or it may even be to pasture-land in the
neighbourhood. During this period of repose large numbers of individuals
gather together on a comparatively small space of ground. They are not
constrained to do so by any shortage of accommodation, nor by any
question relative to food, nor, for the matter of that, by any
circumstance in the external environment; they are brought together
solely, this at least is the impression that one gains, by some
inherited impulse working towards that end. And their subsequent course
of behaviour tends to confirm that impression. For if we watch the
gathering together of the different units of which the flock is
composed, and study more particularly the emotional manifestation which
accompanies their arrival and departure, we shall find that the coming
of a companion arouses some emotion which is expressed by a vocal
outburst that sweeps through the flock.

Now each call, and the Curlew has a great variety, is not only peculiar,
generally speaking, to certain occasions, but is accompanied by a
specific type of behaviour, whence we can infer in broad outline the
type of emotion which is aroused. Thus we come to recognise fear, anger,
or sexual emotion, by just the particular sound which is emitted. But
even if we are going too far in referring particular calls to particular
emotions, we can, without a doubt, divide them into two broad
categories--those which are pleasurable and those which are the reverse.
And we need have no hesitation in placing the particular call to which I
allude in the first of these two categories, not only on account of the
nature of the sound produced, but because the activities which are
aroused are not such as normally accompany irritation. This is well seen
if the behaviour of different individuals be closely observed. After
resting on one leg for some time, first one and then another is seized
with cramp, and running a few yards