During the winter months the advent of mild weather will often break up the packs for a while, and many cases have been reported of birds being scattered over the moor in pairs even in the months of November, December and January; but with the return of wintry conditions their gregarious habits assert themselves even up to the commencement of the nesting season.
The reason why Grouse should pack in winter has often been discussed. The most favourite explanation is that they combine with a view to obtaining Reason for
packing. food in time of scarcity. Another theory is that, like many other birds and animals, the natural instinct of the Grouse is to congregate in flocks, and that this instinct is only departed from to meet the requirements of the breeding season. It is probable that various motives induce the birds to congregate in packs. Some of these motives may be briefly mentioned, (a) To get on to the high bare tops out of the wet—it is observed that Grouse are always more packed after wet weather. (b) To go down to feed on the cornfields; Grouse are seldom found feeding singly on the stooks; this may be due to the natural timidity of the wild bird, which makes it fear to resort to the unwonted feeding-ground unless supported by numbers. The same rule applies with even greater force to the case of birds leaving their own ground and wandering far afield in search of food; such migrations never take place except in large packs, (c) Owing probably to the same cause. Grouse invariably tend to pack after they have been much disturbed, especially by driving, on moors which for some reason have not been shot over for a season; the birds do not pack until late in the year. (d) In dry weather small packs of two or three coveys are found at or near the springs even on August 12th.
Undoubtedly, the most common cause of packing is scarcity of food. It has already been remarked that during the winter months the feeding area on every moor is restricted to those parts where the heather is of such a character as to resist the effects of frost and cold; hence the birds tend to concentrate upon these food centres.
The habit of packing is probably indirectly connected with the question of disease. If we admit that the congestion of a large number of birds upon small areas of moor is conducive to the deposit in dangerous numbers of the larval worms which cause disease on the favourite feeding - grounds of the birds, then it follows that the pack formation is in itself a danger to the health of the stock. This view is supported by the fact that where packing is the exception rather than the rule, as in the west coast of Scotland, disease
