territory and attempt to settle. Is this intolerance merely an exuberant
expression of an instinct which is serviceable in another direction? The
behaviour of the Lapwing scarcely justifies such a conclusion, for all
its actions denote a striving towards some end which we can describe,
and it seems to gain satisfaction only when the ejection of the intruder
has been accomplished.

Many of the Warblers display irritation when approached by other birds
which we should scarcely expect would arouse their hostility. The
Hedge-Sparrow, for example, is frequently regarded with suspicion, and
it is by no means unusual to see it attacked by so small a bird as the
Chiffchaff. The Wood-Warbler is also pugnacious, and will even attack a
pair of Chaffinches. Between the Tit family and some of the smaller
Warblers there are constant exhibitions of hostility; even the Great Tit
is liable to be driven away, but the Blue Tit is especially marked out
for persecution, though doubtless it is well able to hold its own.

The following incident will show how real is the antagonism between
these two families. A Chiffchaff occupied the corner of a small osier
bed, and was particularly aggressive towards other closely-related forms
in its immediate neighbourhood. On two mornings in succession ten Blue
Tits invaded its ground, passing from end to end of it as they wended
their way from tree to tree in search of food. Their presence evoked the
usual hostile response, yet, withal, aroused the fear of the Chiffchaff,
which, at times, appeared to be swayed by conflicting impulses. Now, in
attempting to interpret the nature of the instinct which was evoked, one
has to be guided, in a case of this description, by the similarity of
the response to that which can be observed on other occasions and in
other situations when the intention of the bird is clear. And on this
occasion the Chiffchaff betrayed all the symptoms which normally precede
an attack; it spread its tail, quivered its wings, uttered its
high-pitched note rapidly, hopped from twig to twig, or flew restlessly
from tree to tree, and seemed to be prevented from attacking only by the
number of its opponents. This, indeed, was shown by its subsequent
behaviour, for whenever a Tit became temporarily detached from its
companions it hesitated no longer but forthwith attacked.

There are other species which are no less aggressive than the
Warblers--the Chats for example. The Stonechat regards wit