instinct
arises; and yet the actual number of pairs is on the whole remarkably
constant, and there is no perceptible increase. It seems as if the
numbers of three and two respectively were the maximum the headland
could maintain. But this is no exceptional case; it represents fairly
the conditions which obtain as a rule amongst those species, granting,
of course, a certain amount of variation in the size of each territory
determined by the exigencies of diverse circumstances.

If we take a given district, and devote our attention to the smaller
migrants that visit Western Europe each returning spring for the purpose
of procreation, we shall find that the movements of the males are
subject to a very definite routine. This, however, is not true of every
male; some may be wending their way to breeding grounds at a distance;
others may be seeking the particular environment to which they may be
adapted; others again, having found their old haunts destroyed, may
consequently be seeking new.

Of all this there is evidence. Small parties of Chiffchaffs pass through
a district on their way to other breeding grounds, flitting from hedge
to hedge as they move in a definite direction with apparently a definite
purpose; Reed-Warblers settle in a garden or plantation, eminently
unsuited to their requirements, and disappear; Wood-Warblers arrive in
some old haunt, and finding it no longer suitable for their purpose,
seek new ground. So that plenty of individuals are always to be found,
which, for the time being at least, are wanderers.

In the district which I have in mind, the wandering males form only a
small part of the incoming bird population. The majority of individuals
that fall under observation are those that have made this particular
district their destination; and in doing so, they may possibly have been
guided by their experience as owners or inmates of former nests, for it
cannot be doubted that a return to the neighbourhood of the birthplace
would lead to a more uniform distribution and therefore be advantageous,
and the tendency to do so might consequently have become interwoven in
the tissue of the race. How, then, do they behave? A certain amount of
movement, an interchanging of positions, even though restricted to an
area defined, let us say, by experience, might be expected under the
circumstances--that, however, is not what we find; we observe the
available situations plotted out into so many territories, each on