It would be interesting to know, too, whether birds are really as free in the choice of their mates in spring as at first sight appears. They return to the same places, the same favourite hedge, and even the same tree. Now, when the flocks split up into sections as the spring draws near, each section or party seems to revisit the hedge from which they departed last autumn. Do they, then, intermarry year after year? and is that the reason why they return to the same locality? The fact of a pair building by chance in a certain hedge is hardly enough to account for the yearly return of birds to the spot. It seems more like the return of a tribe or _gens_ to its own special locality. The members of such a _gens_ must in that case be closely related. As it is not possible to identify individual birds, the difficulty of arriving at a clear understanding is great. Why, again, do not robins pack? Why do not blackbirds, and thrushes, go in flocks? They never merge their individuality all the year round. Even herons, though they fish separately, are gregarious in building, and also often in a sense pack during the day, standing together on a spit or sandbank. Rooks, starlings, wood-pigeons, fieldfares, and redwings, may be seen in winter all feeding in the same field, and all in large flocks. Some evidence of a supposed tendency to intermarry among birds may perhaps be deduced from the practice of the long-tailed titmouse. This species builds a nest exactly like a hut, roof included, and in it several birds lay their eggs: as many as twenty eggs are sometimes found; fourteen is a common number. Here there is not only the closest relationship, but a system of community. This tit has a way sometimes of puffing up its feathers--they are fluffy, and in that state look like fur--and uttering a curious sound much resembling the squeak of a mouse; hence, perhaps, the affix `mouse' to its name. The tomtit also packs, and flies in small parties almost all the year round. They remain in such parties until the very time of nesting. On March 24th last, while watching the approach of a snowstorm, I noticed that a tall birch tree--whose long, slender, weeping branches showed distinctly against the dark cloud--seemed to have fruit hanging at the end of several of the boughs. On going near I counted six tomtits, as busy as they could be, pendent from as many tiny drooping boughs, as if at the end of a string, and swinging to and fro as the rude blast struck the tree. The six in a few minutes increased to eight, then to nine, then to twelve, and at last there were fourteen together, all dependent from the very tiniest drooping boughs, all swinging to and fro as the snow-flakes came silently floating by, and all chuckling and calling to each other. The ruder the blast and the more they swung--heads downwards--the merrier they seemed, busily picking away at the young buds. Some of them remained in the tree more than an hour.