Page:Popular Science Monthly Volume 7.djvu/201

Rh from some tall cedar or tangled brier-patch breaks the dead silence, and we mark the arrival of the first spring songster of its kind. Did it reach us at sunset, and, resting a few hours, then announce its presence with its cheery song?

Both by day and by night, it may be, they come, but why at all by night, if so, must ever be a great mystery in the strange habit of migration.

Let us next study our birds during the autumn.

A careful examination of the many notes, jotted down at irregular intervals, during the months of September, October, and November, with respect to the departure south of such of our birds as are summer residents, and of some that, having passed the summer in regions far to the north, are now, likewise, seeking their accustomed winter-quarters, indicates a similar apparent regularity in the southward movements of our birds as in spring, and at the same time an actual degree of variation in the dates of departure exceeding the irregularity of the dates of arrival.

If we consider the several circumstances that would necessarily influence their migratory movements, this actual irregularity, in autumn, is just what should be expected; but in the spring, as every bird returns to its own home and former nest, if possible, they will not linger on the way, as they know too well the length of the journey, and the coming duties of incubation speed them on, and we wonder why they are not more regular in their movements. In autumn, all this is changed. Now nothing need hurry them, and, so long as they find an abundance of food, they leisurely move along, just keeping ahead, as it seems, of the chilling frosts of the coming winter, which they can easily endure, but which robs them of the food they must have. This is especially true of insect-eating birds. Considered in this light, we are not surprised to find, then, as a rule, that the warblers, swallows, and such other birds as depend wholly upon insects for their sustenance, leave more promptly and in larger numbers, at one time, than do granivorous birds, and those that can subsist on seeds, while they consume insects so long as they can find them.

The weather, both during September and October, is exceedingly variable, and this fact causes the southward movements of the migratory, insect-eating birds equally so, inasmuch as these birds are not larvae-hunting species, but depend upon insects that can be caught upon the wing, or are to be found resting upon the leaves and twigs of the trees; therefore, just so long as the heavy white frosts are delayed, these insectivorous birds will linger with us. Up to a certain date, about October 1st on the average, these birds largely increase in numbers, consequent upon the daily accession of those from the north, and after the maximum is reached (October 1st or earlier, in accordance with the weather), their number steadily decreases, until but a few stragglers remain.