All this time I had been in correspondence with my friend before referred to, who was studying a similar roost,[15] —in Belmont,—which proved to be more populous than mine, as was to be expected, perhaps, the surrounding country being less generally wooded. It was a mile or more from his house, which was so situated that he could sit upon his piazza in the evening and watch the birds streaming past. On the 11th of August he counted here 556 robins, of which 336 passed within five minutes. On the 28th he counted 1180, of which 456 passed within five minutes,—ninety-one a minute! On the 2d of September, from a knoll nearer the roost, he counted 1883 entries.

This gathering, like the one in Melrose, was greatly depleted by the middle of September. "Only 109 robins flew over the place to-night," my correspondent wrote on the 25th, "against 538 September 4th, 838 August 30th, and 1180 August 28th." Two evenings later (September 27th) he went to the neighborhood of the roost, and counted 251 birds,—instead of 1883 on the 2d. Even so late as October 9th, however, the wood was not entirely deserted. During the last month or so of its occupancy, the number of the birds was apparently subject to sudden and wide fluctuations, and it seemed not unlikely that travelers from the north were making a temporary use of the well-known resort. It would not be surprising if the same were found to be true in the spring. In April, 1890, I saw some things which pointed, as I thought, in this direction, but I was then too closely occupied to follow the matter.

How early in the season does this nightly flocking begin? This question often presented itself. It was only the middle of July when the Cambridge roost was found in full operation, though at that time many robins must still have had family duties, and some were probably building new nests. Next summer, we said, we would try to mark the beginnings of the congregation.

My own plans to this end came near being thwarted. In December I was dismayed to see the owner of the wood cutting it down. Happily some kind power stayed his hand when not more than a third of the mischief was done, and on the 29th of June, 1890, while strolling homeward along the highway, listening to the distant song of a veery, I noticed within five or ten minutes seventeen robins making toward the old rendezvous. On the following evening I stood beside the ice-pond and saw one hundred and ninety-two robins enter the wood. The flight had begun before my arrival, and was not entirely over when I came away. Evidently several hundreds of the birds were already passing their nights in company. In my ignorance, I was surprised at the early date; but when I communicated my discovery to the Belmont observer, he replied at once that he had noticed a movement of the same kind on the 11th of June. The birds, about a dozen, were seen passing his house.

Thinking over the matter, I began to ask myself—though I hesitate about making such a confession—whether it might not be the adult males who thus unseasonably went off to bed in a crowd, leaving their mates to care for eggs and little ones. At this very moment, as it happened, I was watching with lively sympathy the incessant activities of a female humming-bird, who appeared to be bringing up a family (two very hungry nestlings), with no husband to lift a finger for her assistance; and the sight, as I fear, put me into a cynical mood. Male robins were probably like males in general,—lovers of clubs and shirkers of home duties. Indeed, a friend who went into the roost with me, one evening, remarked upon the continual cackling in the treetops as "a very social sound;" and upon my saying something about a sewing circle, he answered, quite seriously, "No, it is rather like a gentleman's club." But it would have been unscientific, as well as unchristian, to entertain an hypothesis like this without putting its soundness to some kind of test. I adopted the only plan that occurred to me,—short of rising at half past two o'clock in the morning to see the birds disperse. I entered the wood just before the assemblage was due (this was on the 9th of July), and took a sheltered position on the eastern edge, where, as the robins flew by me, or alighted temporarily in the trees just across the brook, they would have the sunlight upon their breasts. Here, as often as one came sufficiently near and in a sufficiently favorable light, I noted whether it was an adult, or a streaked, spotted bird of the present season. As a matter of course, the number concerning which this point could be positively determined under such conditions was very small,—only fifty-seven altogether. Of these, forty-nine were surely birds of the present summer, and only eight unmistakable adult males. If any adult females came in, they passed among the unidentified and uncounted. [16] I was glad I had made the test. As a kind-hearted cynic (I confess to being nothing worse than this), I was relieved to find my misanthropic, or, to speak more exactly, my misornithic, notions ill founded. As for the sprinkling of adult males, they may have been, as a "friend and fellow woodlander" suggests, birds which, for one reason or another, had taken up with the detestable opinion that "marriage is a failure."

During the month of July, 1890, I made frequent counts of the entries at the eastern end of the roost, thinking thus to ascertain in a general way the rate at which its population increased. On the whole, the growth proved to be fairly steady, in spite of some mysterious fluctuations, as will be seen by the following table:—

July 3247 July 161064
" 5383 " 171333
" 6356 " 191584
" 10 765 " 221520
" 12 970 " 231453
" 14 1120 " 272314

After July 6th all the enumerations were made with the help of another man, though we stood side by side, and covered no more ground than I had hitherto attempted to compass alone. The figures of the 27th were far in excess of any obtained in 1889, and for a day I was disposed to take seriously the suggestion of a friend that some other roost must have been broken up and its members turned into the Melrose gathering. But on the evening of the 28th I tried a count by myself, and made only 1517 birds! The conditions were favorable, and the robins came, as they had come the night before, in flocks, almost in continuous streams. The figures had fallen off, not because there were fewer birds, but because I was unable to count them. They were literally too many for me. The difficulties of the work, it should be explained, are greatly enhanced by the fact that at the very corner where the influx is largest none of the low-flying birds can be seen except for a second or two, as they dart across a bit of sky between the roost and an outlying wood. To secure anything like a complete census, this point must be watched continuously; and meantime birds are streaming in at the other corner and shooting over the distracted enumerator's head, and perhaps dropping out of the sky. I conclude, therefore, not that the roost had increased in population, but that my last year's reckoning was even more inadequate than I then supposed. Even with two pairs of eyes, it is inevitable that multitudes of birds should pass in unnoticed, especially during the latter half of the flight. I have never had an assistant or a looker-on to whom this was not perfectly apparent.

As I stood night after night watching the robins stream into this little wood,—no better, surely, than many they had passed on their way,—I asked myself again and again what could be the motive that drew them together. The flocking of birds for a long journey, or in the winter season, is less mysterious. In times of danger and distress there is no doubt a feeling of safety in a crowd. But robins cannot be afraid of the dark. Why, then, should not each sleep upon its own feeding grounds, alone, or with a few neighbors for company, instead of flying two or three miles, more or less, twice a day, simply for the sake of passing the night in a general roost?

Such questions we must perhaps be content to ask without expecting an answer. By nature the robin is strongly gregarious, and though his present mode of existence does not permit him to live during the summer in close communities,—as marsh wrens do, for example, and some of our swallows,—his ancestral passion for society still asserts itself at nightfall. Ten or twelve years ago, when I was bird-gazing in Boston, there were sometimes a hundred robins at once about the Common and Garden, in the time of the vernal migration. By day they were scattered over the lawns; but at sunset they gathered habitually in two or three contiguous trees, not far from the Frog Pond and the Beacon Street Mall (I wonder whether the same trees are still in use for the same purpose), where, after much noise and some singing, they retired to rest,—if going to sleep in a leafless treetop can be called retiring.