GENERAL SUMMARY AND CONCLUDING REMARKS
as Professor Groos says in referring to a similar habit of the Wren, is only one step further in the same direction. Is the habit confined to those males only which share the task of constructing the nest with the female? We must know this before we can hope to reach any definite conclusion, and I have not sufficient data to go upon. But if it were so, we need hardly, one would think, regard the habit as a detached and inexplicable incident in the sexual life of the bird, but as a genuine step on the part of the male towards building the nest.
We come now to the actual construction of the nest. Nothing in nature is perhaps more wonderful than these delicate pieces of architecture, adapted with such a wealth and diversity of form to their surroundings. In some species the work of construction is shared by both sexes, in others the female is responsible for the greater part, if not for the whole. So industrious is the male Whitethroat that he may build one or more nests even before a female has arrived, a peculiarity to which I have referred, and which no doubt he shares with other species. What is the meaning of such exceptional industry? In the opinion of Professor Groos, it must be included in the category of "play," but, as the history of the Whitethroat shows, such nests may be structurally complete and ultimately made use of for the purpose of reproduction. The females of the Willow Warbler and Garden Warbler sometimes build one or more partial nests before the final structure is commenced. We can trace the reason of this in some instances. The Willow Warbler that built four nests deserted the first, I believe, because of constant persecution by the adjoining male. Some, however, say that these loosely ordered platforms represent the initial attempts of young birds, just as the Reed Warbler's nest woven to three reeds instead of more might be attributed to a similar lack of experience. Could a few strands of decayed vegetation laid crosswise here and there afford the necessary data for experience? And when we here speak of experience,
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