One of the first things to strike the observer is the uniformity with which such pilgrims arrive during the night. He goes his rounds late in the afternoon, and there is, no sign of anything unusual; but the next morning the grounds are populous,--thrushes, finches, warblers, and what not. And as they come in the dark, so also do they go away again. With rare exceptions you may follow them up never so closely, and they will do nothing more than fly from tree to tree, or out of one clump of shrubbery into another. Once in a great while, under some special provocation, they threaten a longer flight; but on getting high enough to see the unbroken array of roofs, on every side they speedily grow confused, and after a few shiftings of their course dive hurriedly into the nearest tree. It was a mistake their stopping here in the first place; but once here, there is nothing for it save to put up with the discomforts of the situation till after sunset. Then, please heaven, they will be off, praying never to find themselves again in such a Babel.
That most of our smaller birds migrate by night is by this time too well established to need corroboration; but if the student wishes to assure himself of the fact at first hand, he may easily do it by one or two seasons' observations in our Common,--or, I suppose, in any like inclosure. And if he be blest with an ornithologically educated ear, he may still further confirm his faith by standing on Beacon Hill in the evening--as I myself have often done--and listening to the _chips_ of warblers, or the _tseeps_ of sparrows, as these little wanderers, hour after hour, pass through the darkness over the city. Why the birds follow this plan, what advantages they gain or what perils they avoid by making their flight nocturnal, is a question with which our inquisitive friend will perhaps find greater difficulty. I should be glad, for one, to hear his explanation.
As a rule, our visitors tarry with us for two or three days; at least I have noticed that to be true in many cases where their numbers, or size, or rarity made it possible to be reasonably certain when the arrival and departure took place; and in so very limited a field it is of course comparatively easy to keep track of the same individual during his stay, and, so to speak, become acquainted with him. I remember with interest several such acquaintanceships.