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
