Why birds and beasts flock, no doubt, is for mutual protection from natural foes. One has heard of swallows nesting on a cliff beneath an eagle's eyrie, yet having nothing to fear from the eagle's attack because of their combination; and every one knows how a party of small birds will defy a hawk, or will mob and rout a cuckoo or a day-flying owl. Possibly the reason for the great congregation of sparrows in one chosen tree in a London square is mutual protection from cats. Food is a most important factor in flocking; the keeper knows that the scarcer the food of partridges the greater is their tendency to pack. Birds may pack at night for mutual warmth--as when titmice snuggle on branches, and wrens, to the number of ten or twenty, crowd a hole in the thatch. Partridges gain something in warmth in snowy weather by their habit of jugging at night--a good covey on a yard of ground. But examination of the spot where they have passed the night shows that the main pack has been divided into comparatively small parties, in the same way as there were small parties among the great herds of buffalo that travelled as one column across the plains of America. Sheltered hollows are naturally chosen for jugging, where the keen edge of the wind passes over the birds' heads. There is not always safety or benefit in numbers; a flock may attract foes where individuals would pass unnoticed, or may make short work of food which would keep an individual for many days. With insects, great congregations may be harmful, if an advantage to their bird enemies. Presumably, flocking is a matter of general convenience. During the first fortnight of October little parties of fieldfares from Scandinavia drift over the fields, chuckling in their throaty way, redwings are seen, our wood-pigeons are reinforced by countless thousands from overseas, snipe come in, woodcock will soon be here, parties of goldcrests, newly arrived, cry their sharp notes among the larches, and the winter flocks of tits, with goldcrests, tree-creepers, and nuthatches busily move in the woods. Everywhere birds are in flocks. Chaffinches, greenfinches, and sparrows move in vast congregations, plovers circle in clouds above the fallows, flocks of rooks unite in the evening and thousands upon thousands of starlings rise, fall, and circle in perfect unison, filling the air with the rushing noise of wings. * * * * * The Companies of Rats