WILLOW WARBLER
not yet alluded is uttered at times of anxiety, or seemingly for no ostensible reason. It is very similar to the corresponding note of the Chiff-chaff, and very difficult to distinguish therefrom, consisting of two notes uttered in a plaintive key, but more slowly or rather not so briskly as those of the other bird.
Their food is similar to that of the Chiff-chaff, and consists almost entirely of insects. Occasionally they peck at the fruit in gardens, and can often be found in the autumn in the elder bushes, but I do not recollect having seen them actually feeding on the berries. Their principal food when they arrive consists of the various species of Chironomidæ; these they seek for diligently, examining large and small branches, buds, and leaves. Since they are later than the Chiff-chaff in arriving at their breeding grounds, they probably do not suffer so much from scarcity of food brought about by abnormal climatic conditions. Nevertheless they are compelled sometimes to face frost and even snow, and they then lapse into silence, less able apparently to withstand the cold, or more probably less capable of replacing their usual diet by more minute and hardy insects. Later in the season larvæ form their staple diet, especially those of the oak-leaf roller moth (Tortrix viridana). The young are principally fed on larvæ.
