Coming together at nesting-time is so common with most birds that more examples are scarcely needed. Our trees are crowned with groups of crows’ nests; our hedges are full of nests of smaller birds; our farmhouses give shelter to colonies of swallows; our old towers are the refuge of hundreds of nocturnal birds; and pages might be filled with the most charming descriptions of the peace and harmony which prevail in almost all these nesting associations. As to the protection derived by the weakest birds from their unions, it is evident. That excellent observer, Dr. Couës, saw, for instance, the little cliff-swallows nesting in the immediate neighbourhood of the prairie falcon (Falco polyargus). The falcon had its nest on the top of one of the minarets of clay which are so common in the canyons of Colorado, while a colony of swallows nested just beneath. The little peaceful birds had no fear of their rapacious neighbour; they never let it approach to their colony. They immediately surrounded it and chased it, so that it had to make off at once.28
Life in societies does not cease when the nesting period is over; it begins then in a new form. The young broods gather in societies of youngsters, generally including several species. Social life is practised at that time chiefly for its own sake—partly for security, but chiefly for the pleasures derived from it. So we see in our forests the societies formed by the young nuthatchers (Sitta caesia), together with tit-mouses, chaffinches, wrens, tree-creepers, or some woodpeckers.29 In Spain the swallow is met with in company with kestrels, flycatchers, and even pigeons. In the Far West of America the young horned larks live in large societies, together with another lark (Sprague’s), the skylark, the Savannah sparrow, and several species of buntings and longspurs.30 In fact, it would be much easier to describe the species which live isolated than to simply name those species which join the autumnal societies of young birds—not for hunting or nesting purposes, but simply to enjoy life in society and to spend their time in plays and sports, after having given a few hours every day to find their daily food.
And, finally, we have that immense display of mutual aid among birds—their migrations—which I dare not even enter upon in this place. Sufficient to say that birds which have lived for months in small bands scattered over a wide territory gather in thousands; they come together at a given place, for several days in succession, before they start, and they evidently discuss the particulars of the journey. Some species will indulge every afternoon in flights preparatory to the long passage. All wait for their tardy congeners, and finally they start in a certain well chosen direction—a fruit of accumulated collective experience—the strongest flying at the head of the band, and relieving one another in that difficult task. They cross the seas in large bands consisting of both big and small birds, and when they return next spring they repair to the same spot, and, in most cases, each of them takes possession of the very same nest which it had built or repaired the previous year.31
This subject is so vast, and yet so imperfectly studied; it offers so many striking illustrations of mutual-aid habits, subsidiary to the main fact of migration—each of which would, however, require a special study—that I must refrain from entering here into more details. I can only cursorily refer to the numerous and animated gatherings of birds which take place, always on the same spot, before they begin their long journeys north or south, as also those which one sees in the north, after the birds have arrived at their breeding-places on the Yenisei or in the northern counties of England. For many days in succession—sometimes one month—they will come together every morning for one hour, before flying in search of food—perhaps discussing the spot where they are going to build their nests.32 And if, during the migration, their columns are overtaken by a storm, birds of the most different species will be brought together by common misfortune. The birds which are not exactly migratory, but slowly move northwards and southwards with the seasons, also perform these peregrinations in flocks. So far from migrating isolately, in order to secure for each separate individual the advantages of better food or shelter which are to be found in another district—they always wait for each other, and gather in flocks, before they move north or south, in accordance with the season.33
Going now over to mammals, the first thing which strikes us is the overwhelming numerical predominance of social species over those few carnivores which do not associate. The plateaus, the Alpine tracts, and the Steppes of the Old and New World are stocked with herds of deer, antelopes, gazelles, fallow deer, buffaloes, wild goats and sheep, all of which are sociable animals. When the Europeans came to settle in America, they found it so densely peopled with buffaloes, that pioneers had to stop their advance when
