Abstract
The first morning calls or songs of 14 birds common in the vicinity of Washington, have been recorded, and plotted in relation to the curves of Civil Twilight and sunrise. The data indicate that all the birds are highly sensitive to the coming day, some species appreciating very low light intensities with considerable accuracy. Certain analogies are drawn between this behavior of the birds and the migration urge. The opinion is expressed that the exactness of the migratory movements, like the exactness of the timing of the first morning expressions, is in some manner dependent upon the sun.

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