BRITISH WARBLERS
of experiments by placing a leaf in the nest in order to see in what manner the parents would adapt themselves to the unusual conditions thus presented; whether, as in the case of the Whitethroat, they would treat it as if it were fæces ejected by the young, or whether they would recognise the nature of the obstruction. On the whole, there is little difference between the behaviour of the two species. I have never seen a Reed Warbler actually swallow a leaf, but its efforts to do so are equally as pronounced as those of the Whitethroat, and its failure may be due to physical reasons. The leaf is picked up and held in the bill, while at the same time the movements necessary for swallowing are performed; it is then perhaps dropped, but again picked up and finally carried away. When a number of leaves are placed in the nest at the same time, those that slip in between the young and are pushed to the bottom are allowed to remain. If a leaf of the same size as the interior of the nest is placed over the young, thus completely hiding them, the female on her return takes little notice. There is a slight examination and slight bewilderment, but nothing more; then she settles down upon the nest and attempts to brood in the usual manner. However, the discomfort, and perhaps the feeling that her legs and feet are not in their proper position and her feathers not satisfactorily covering her young seem to make her restless, and in her struggles to put matters right the leaf is soon pushed over the edge.
Incidents sometimes occur of so little importance in themselves that they may almost seem to savour of triviality, but whenever they are in the nature of a check to the normal routine of activities, whenever, that is to say, adaptation to unusual circumstances is required, then such incidents in themselves may be said to constitute an experiment, the result of which is of relatively equal value in enabling us to judge of the mentality of the actor as the result of an experiment planned and carried out by the human mind. I can recall two such incidents, both of which occurred while food was
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