else is subservient, and the supply of the necessary sustenance may,
under certain conditions, become a difficulty which can only be met by
energy and resource. After the long night the sensation of hunger is
strong, and the birds, on awakening, fly to the accustomed feeding
grounds, returning again in the evening to the selected spot, and by
frequent repetition a routine becomes established. Thus the behaviour of
each individual is determined not only by the powerful gregarious
impulse but also by the habits formed in connection therewith during
many weeks in succession. Now with the rise of the appropriate organic
state, the disposition to seek the breeding ground and there to
establish itself becomes dominant in the male. But the process is a
gradual one. There is no need, as happens amongst the migrants, for the
period of organic change to conform rigidly to the growth of any
particular condition in the environment, and hence for a time the bird
oscillates between two modes of behaviour--between that one organised by
frequent repetition and that one determined by the functioning of this
new disposition.

To look at the matter broadly, it is scarcely likely that so definite a
mode of behaviour would recur with such regularity, generation after
generation, in the individuals belonging to so many widely divergent
forms, if it had no root in the inborn constitution of the bird. But the
law of habit formation has its part to play also. By itself it is
inadequate; yet it probably does assist very materially in adding still
greater definition, and it probably is responsible in a large measure
for determining the limits of the territory according to the conditions
of existence of the species--thus the Falcon seeks its prey over wide
tracts of land, and, by hunting over certain ground repeatedly,
establishes a routine, which broadly fixes the area occupied; the
Woodpecker cannot find food upon every tree, and every forest does not
contain the necessary trees, and therefore the bird regulates its flight
according to the position of the trees; and the Warbler, finding food
close at hand, does not need to travel far, and the area it occupies is
consequently small.

So that the most likely solution of the problem will be found in a
combination of our second and third propositions; that is to say, in an
initial responsive behaviour provided for in the inherited constitution
of the nervous system, and in a definiteness acquired b