BRITISH WARBLERS
been the case, since the young were but a few hours old and required the care and assistance of a parent for some weeks. The approach of a member of another species is sometimes the signal for an outburst of excitement, and may result in a spirited attack upon the intruder. Of no bird is the approach so much resented as that of the Cuckoo, and so long as it remains in the neighbourhood of the nest the excitement, of the male especially, knows no bounds. If it happens to pass amongst the trees above the nest the male follows in pursuit, uttering a curious jumble of sounds intermingled with which are parts of his song, and upon his return moves uneasily from bush to bush, expressing his excitement by jerking, fluttering, spreading, and waving his wings, and at the same time fully expanding his tail. His attitude at such a time differs only in degree from that during sexual activity, the wings being more fully expanded and the tail fanned out instead of being slightly spread. It is curious that in the case of both the Willow Warbler and the Chiff-chaff there should be such resentment shown at the presence of a Cuckoo, and interesting also that the resultant expression of the emotion should be identical. If these two species were especially singled out by the Cuckoo as foster-parents for its young we could better understand their behaviour, but according to my experience this is not the case.
Of the two the female is the more timid. She it is who is suspicious when one approaches the nest, fluttering around for some time before she can gain sufficient courage to enter. The male is not so easily perturbed; he may hesitate before he carries food to his young and performs the necessary duties, but it is not for long. The female often finds courage in following in his wake, and therefore enters the nest immediately after, if not at the same time with him. She, however, shows all the while by her actions that her suspicions are not allayed, casting frequent hurried glances this way or that. The young remain in the nest about eleven days. For the first few days the female spends much of her time brooding,
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