The Grouse in Health and in Disease/Chapter III/Part I
the changes in plumage in the red grouse in health and in disease
By Edward A. Wilson
Part I. — Plumage Changes of the Cock Grouse
When a large number of skins of the cock Grouse are arranged together, side by side, according to the month in which the birds were killed, it will be found that, even taking into account the differences of well-marked local variations in plumage, the series can readily be divided into two very distinct sets.
There is first a very marked uniformity in the plumage of the cock birds killed from the middle of November to the end of June; and Seasonal
plumage. likewise amongst those killed from the end of June to the middle changes of of November.
These two periods, November to June and June to November, mark the two seasonal changes of plumage in the cock Grouse.
The first is a plumage worn throughout the winter, as well as during the courting and breeding season of the spring.
The second is a plumage worn throughout the late summer and early autumn.It is necessary to lay stress upon this general broad division of the cock Grouse's plumage, and if a large number of skins can be arranged as suggested the time at which the Grouse has definitely changed from the one plumage to the other cannot possibly be overlooked. The birds obtained at the end of May are definitely in the darker and redder winter plumage, and those procured at the end of June are definitely in the paler and more buff-coloured summer plumage; those killed at the beginning of October are still partly in the paler summer plumage, and by the end of November all are in the darker winter plumage.
It must, however, be added, that there is hardly a month in the whole year, or a Grouse skin in a collection of many hundreds covering every month of the year, in which one plumage only can be found unmixed with the other. This fact accounts largely for the misunderstanding which at one time existed, but which has now, we hope, been satisfactorily settled, in respect of the whole vexed question of moult and plumage changes in the Red Grouse, and their proper interpretation.
Without referring in detail to the points upon which differences of opinion have before now arisen, it may be shown that much misunderstanding upon Reasons for
misunderstanding this difficult subject is based upon a different rendering of facts into words, facts which were recognised and perfectly well explained by Mr. Ogilvie-Grant in 1893. Both he and Mr Millais have made the subject of plumage changes in the game-birds, and especially in the Grouse, a special study, and it must be admitted that there are very few points upon which they have touched which seem to require further explanation and still fewer points, if any, which can be brought to light for the first time in connection with the plumage changes of the Red Grouse. A monograph on the Red Grouse, such as the Report of the Grouse Disease Inquiry, would, however, be obviously incomplete without an account of the plumage changes of the bird itself; and it so happens that during the six years of the Grouse Disease Inquiry's existence the collection of some six hundred Red Grouse skins, representing every age, phase, and change of plumage in that bird, has given a unique opportunity for an independent revision of the work already done — an opportunity such as has never occurred before in the study of any single species of Effect of
changes. British bird for observing the effect of disease upon moult and feather growth. So it happens that although the work as it stands has been so nearly completed by the labours of the two ornithologists already mentioned, there are still points of interest to which attention may be drawn, especially in connection with the marked effect which parasitism and other wasting diseases have upon the moult and growth of feathers, and it is to this influence of disease that attention will be particularly drawn in the present paper.
It is important to note the extraordinary irregularities which so commonly occur in the plumage of the Red Grouse owing to disease, whereby the deferred moult becomes in some years almost the rule, and the rule of health becomes almost the exception. It is a very difficult matter, Effects of
disease. indeed, for any one who has not had the opportunity of examining an extensive series of Grouse skins, in disease as well as in health, and covering every month of the year, to come to any true conclusion about the moult. Diseased conditions often entirely mask the normal plumage changes from time to time, and it is far more important to realise this than to examine thousands of more or less healthy birds shot in the ordinary course of events in the shooting season. A study of abnormal plumage changes in diseased Grouse is essential if the discrepancies which arise in the moult of what are often wrongly considered normal birds, are ever to be explained. Once this point is grasped the question becomes much simpler, and it is because the Grouse Disease Committee has had such ample opportunity for studying both sides of the question that it has been deemed necessary to enter into these plumage changes at such length.
It is almost incredible that a moult should be deferred from one season to another, or even to a third, and that the right plumage should eventually be produced if the bird, by means of good food and good weather, is at Effect of
legs. last enabled to recover its health and grow any new feathers at all. It is interesting, and to some people, such as sportsmen and gamekeepers, even useful to know that bare featherless legs and feet, which have so long been considered a sure sign of disease in the Red Grouse, may, in certain months of the year, be a natural accompaniment of really good health, while thickly feathered legs in the same month are a sure sign of deferred moult and of sickness. It is only when the proper season for the moult of the leg and foot-feathering is completely understood that we begin to understand the reason for attaching an unfavourable prognosis to heavy leg-feathering when the legs should have been featherless, and an equally favourable prognosis to bare legs when the legs should certainly have been bare (PI. xiii., Figs. 1-2).
Mr Millais also, in speaking of the cock Grouse, makes use of the expression autumn plumage which, he says, appears late in June; and he adds that the autumn plumage, together with the "spring feathers" (or what Mr Ogilvie-Grant considers the first beginning of the autumn plumage on the Grouse's neck), remain till the main moult in August and September.
Mr Millais also makes the following statement, which appears to be based on a misinterpretation. He says: "as a matter of fact the male Grouse sheds in September and August a plumage which is a mixture of its winter, spring, and eclipse feathers."
These so-called "spring" and "eclipse" feathers are no doubt, as Mr Ogilvie-Grant holds, the commencement of the plumage which is completed gradually during the summer months, and which he has described as the autumn plumage. It is naturally a little misleading to find the autumn plumage beginning to appear in early summer, but so long as the term is understood to mean the paler, more buff-coloured plumage with bolder bars of black, which begins to appear first on the neck of the cock at the end of May or early in June, and is eventually cast for the winter plumage in October, there need be no real misunderstanding.
That feathers of the previous winter plumage should be mentioned in speaking of the moult of this autumn plumage is also quite intelligible, since the old winter plumage of the breast and abdomen is being quickly shed and replaced by a similar new winter plumage at the time when the autumn plumage on the rest of the body is being cast. There are in addition very frequently a few feathers of the copper-red plumage on the chin really belonging to and remaining over from the previous winter plumage.
Instead of going into further details, however, with regard to the two moults and plumages of the cock Grouse, it will be simpler at this point to take its plumage changes in detail, successively month by month, explaining as nearly as possible what can be gathered from the examination of a series of skins such as has been brought together by the Committee, including as it does a great number of specimens in all stages of disease as well as in health.
These illustrate every month of the year and most of the local variations to be found in England, Scotland, and Ireland; and there are a sufficient number of sick as well as healthy birds to show the very great influence that disease has in altering the individual capacity for feather growth. Unless this effect, which results as a rule in the Red Grouse from excessive parasitism, is fully recognised, there will always be misunderstandings upon the moult of this bird, for almost every Grouse in the country is to some extent infested with parasitic worms, and there are years when irregularity of moult is the rule rather than the exception. Moreover, it so happens that in autumn, when birds are being shot in large numbers, the survivors of the two worst months of the year for "Grouse Disease" mortality, that is, the survivors of May and June, are all convalescing; but they are convalescing with their plumage changes all retarded and put completely out of order and routine. In this way it is possible in September to kill two birds on the same day, both of which have the chestnut-coloured feathers of the winter plumage on the chin and throat; but upon examination it may be seen that in one bird the edges of these feathers are frayed and worn and the colour faded, showing that they have survived from the previous winter plumage; whereas in the other bird they are hardly free of the scaly sheaths in which they grew, and are really precocious feathers of the coming winter plumage. This is only one of the many traps which result from the deleterious influence which disease exerts upon a bird's capacity for feather growth and replacement, and so upon the regularity of its moult.
There is another point to which attention must be drawn before entering upon a systematic description of the monthly changes of feather in the cock Grouse. It is as to whether the autumn plumage of the cock can "Eclipse
plumage. be correctly described as an "eclipse" plumage, comparable as it obviously is in character with the spring breeding plumage in the hen, but appearing just two months later and after the breeding season. In each sex the general change from winter to summer may be described as a change from a more richly pigmented, darker, black and chestnut, or rufous-chestnut plumage with rather fine transverse black markings, sometimes almost vermiculate in character, to a less richly pigmented, paler, buff or rufous-buff" or tawny-buff" plumage with characteristically broad black bars and transverse markings.
There is without doubt a general broad resemblance, firstly between the cock and the hen Grouse when the former is in its "winter plumage" and the latter in its "autumn plumage"; and, secondly, between the cock and the hen Grouse when the former is in its "autumn plumage" and the latter in its "spring plumage."
The perplexing fact is that these general resemblances are not synchronous Cock and
seasons. in the two sexes, a peculiarity first observed by Mr Ogilvie-Grant, for as already pointed out, there is an interval of two months between the moult of the cock and hen.
Again, it might reasonably be expected that, as the Ptarmigan and the Scandinavian Willow Grouse have not two plumages in the year, but three, some suggestion of the third plumage might be forthcoming in the Red Grouse. But the Red Grouse has only two moults. Mr Ogilvie-Grant, however, explains the position by saying that the buff and black plumage of the hen Grouse answers to the spring plumage of the hen Ptarmigan, while the buff and black plumage of the cock Grouse answers to the autumn plumage of the cock Ptarmigan. The grounds for this opinion will be considered later in the light of the possible effect which continued disease may have in permanently altering the season of the moult.
Beginning now with the cock Red Grouse in January, and taking its Cock
January appearance from the ventral aspect first, the uniformity of the series Grouse in is a Very conspicuous feature. Every healthy bird is chestnut or rufous-chestnut and black, with fine, almost vermiculate black cross-lines over it.
(p.z.s. 1910. Pl LXXIX.)
Andre & Sleigh, Ltd.
male grouse, black type, in full winter-plumage.
(p.z.s. 1910. Pl. LXXX.)
Andre & Sleigh, Ltd.
male grouse, red type, in full winter-plumage.
(p.z.s. 1910. Pl. LXXXI)
Andre & Sleigh, Ltd.
male grouse, white-spotted bird of the red type.
(p.z.s. 1910. Pl. LXXXII)
Andre & Sleigh, Ltd.
male grouse, red type, in full winter-plumage with a
few black-centered feathers of the previous
The following points in the cock Grouse of January are characteristic.
- The rich copper-red, generally unbarred feathers of the throat and fore-neck (PI. xvi., Figs. 3 and 4).
- The fine barring of the chestnut, dark rufous-chestnut, or blackish-brown of the back, with the scattered black-centred feathers of the last "autumn plumage."
- The thick, white feathering of the feet and legs, which soon becomes blackened and worn by the "burrens" or "colons," the charred stalks of old burned heather.
- The perfect flight-feathers of the wings and tail.
- The very large claws.
In February the cock Grouse is still in the darker winter plumage. Young, sheathed and growing broad-barred feathers, the remains of February. the "winter plumage," may still occasionally be found on the hind-neck, nape, and head in backward birds.
In March the cock Grouse normally shows no change; but towards the end of the month in exceptional instances individual birds may be found with a few precocious feathers of the autumn plumage making their March. appearance on the back of the head and neck. These are very probably feathers irregularly developed to take the place of those which have been lost during encounters with other males.
In April the cock Grouse still shows no change. In this month there are often greatly increased opportunities for the addition of skins to a collection, April. because it happens to be a month of very high mortality from "disease." The birds are found and can be collected not only by the keepers who are out early in the month in search of fox-earths, and who are generally also burning heather about this time, but also later by the shepherds who are constantly ranging the moor in the lambing time. During the last five years there has been a great accession of Grouse skins to the Inquiry's collection in March with a very large proportion of males badly diseased, and comparatively few birds in perfect health. Therefore, in the series of skins of cock birds representing the month of April, the great majority are very backward. Healthy birds have still the old, rich, red, copper-coloured throat of the winter plumage, and fresh-looking "autumn" feathers round the neck, upper back, and mantle, while the winter and old autumn plumage of the rump and back is bleached and faded. The backward birds are easily picked out, as they have not yet assumed their "winter" plumage, and are still mostly clad in old, worn autumn plumage of the previous year. If an April bird has newly and thickly feathered legs and feet, it means, almost certainly, that the "winter" plumage has been put on very late. The healthy Grouse should now be moulting the feathers of the feet and legs, so that bareness or lack of feathers becomes in them a sign of health in April, and thickly feathered legs a sign of sickness; this is the precise contrary of what has almost become proverbial on the moor, that bare legs indicate disease; though for the later autumn months the saying is quite true.
In May the preponderance of cock birds found dead, and therefore of skins of cock birds in the May collection showing belated moult, is again May. a large one. The healthy cock is still in his much-worn winter plumage, but on the head and neck some feathers of the new autumn plumage are beginning to make their appearance (PI. vi. and vii.).
In June as a rule, the mortality amongst adult birds, due to Strongylosis, is coming to an end; but for the young chicks June and July are June.often fatal months owing to Coccidiosis. Late in June the healthy cock Grouse can at last be said to have changed into his complete "autumn plumage." The winter plumage persists only on the abdomen and lower breast, on the actual chin which is blackish with a few white spots, and on the throat, where a few red feathers still remain. The moulting of the quills and tail feathers commences towards the end
(p.z.s. 1910. Pl. LXXXIII)
Andre & Sleigh, Ltd.
male grouse showing marked beginning of the
autumn-plumage on head and neck.
(p.z.s. 1910. Pl. LXXXIV)
Andre & Sleigh, Ltd.
male grouse changing from winter to autumn-plumage.
postponement. the bird, and one is led to think that this habitual disability in the cock Grouse, which results from Strongylosis during the nesting, courting, and breeding season (a disability which causes the death of about eight cocks to every hen in April and in May), may have caused the alteration in the season of the moult, simply because the vis vitœ of the cock bird, insufficient as we now know it to be at the close of winter for the ordinary calls of reproduction, would be still more disastrously insufficient if preceded by an early moult.
At the present time the cock undoubtedly breeds in the winter plumage, without any further acquisition of new feathers, and, as has recently been pointed out by Mr Ogilvie-Grant, what have been regarded by Mr Millais as new "spring feathers" on the neck are in fact the old autumn feathers, which on that part of the body do not become worn and faded.
That any feather of the Grouse, either in the cock or in the hen, was ever altered as to its pigment either in pattern, or in tone, or in Change in
improbable. any other character, when once it had completed growth and had been cut off from the circulation, is at present an assumption which is not well supported by the physiology of feather growth.
Metchnikoff's observation upon the migration of leucocytes into hair and their action in removing pigment cannot for one moment be adduced as conclusive proof that the same thing may happen in the case of a full-grown feather. While the circulation is active in the feather shaft, and for as long and in so far as it continues, pigmentation may be altered, but once the circulation has ceased beyond the entrance to the base of the shaft, and once that the feather, although still attached to the epidermis, is cut oft' from the circulation in the deeper living layer of the skin, then the feather is no more likely or able to change the pigment which is responsible for its pattern or its colour than would be the same feather had it been plucked out and kept entirely separate from the bird.
Once the feather is full grown, and the circulation in it stopped, there is no reason to believe that any thing can alter it save sunlight and water, and oil supplied as an external unguent from the oil gland. That appearances are most deceptive in this respect must be allowed. Feathers may be collected from the flanks of hen Grouse which show every possible graduation Pigmentation between the almost vermiculate flank feather indicating the perfect winter plumage, and the broad-barred breeding-season flank feather of the summer hen. But it is very much more probable that the growing period of these ambiguous or intermediate feathers is one of great susceptibility to outside conditions, as we know to be the case in respect of the metabolic processes which are taking place within the hen bird at the time. Pigment is indisputably a product of tissue metabolism. It is often probably a mere waste product, but it appears at times to serve a special function notwithstanding. It is also certain that pigment is a production whose appearance, or failure to appear, is open to considerable vicissitudes in consequence of small recognised changes in physiological condition, and of some less easily recognised changes in the general metabolism of the body.
In the hen Grouse during the breeding season we know that pigment production is very actively at work, for we know that a very large amount is being produced for excretion in the pigment glands of the lower part of the oviduct. This pigment, moreover, is precisely of the shade and colour which is characteristic, not of the breeding plumage, but of the winter dress of the hen and the cock Red Grouse. It is normally deposited in abundance on every egg, but on the other hand it may abnormally fail to be deposited or even produced at all, not only in the eggs in the oviduct, but in the circulating blood of the bird's whole system. Thus the feathers, instead of becoming buff or brown, reddish or even black as they proceed in growth, may be any intermediate paler shade of buff, or even white, a character which is due generally to the complete absence of all pigment granules. The place of the pigment in such feathers is probably taken by shining air globules, as it is in the hair and feathers of the majority of white animals and birds. It is thus easier to believe that a sudden check, either by a change of temperature, or by wet and cold, or by want of sunshine, or by change in food, has for the time so far affected the tissue metabolism of the bird that a feather which began to grow upon a circulation lacking pigment particles, and which was therefore originally planned for the paler plumage, may, by a sudden increase in the metabolism of the bird, and so in the output of waste products to the blood, be completed as a feather of the more deeply pigmented plumage, thus producing a feather with the characters of both.
This is a plausible explanation, but is still open to some doubt, for the difference between the broad - banded buff and black flankfeather of the nesting hen, and the dark red-brown finely cross-lined feather of the same bird in winter, is obviously greater as regards pigment distribution than as regards the actual quantity of pigment deposited in the feathers.
If there are, as has been held, distinct pigments, such, for example, as buff, black, and orange-red, in the various colour-tones of the Red Grouse, it becomes easier to see that the loss of the red pigment, which is utilised for the eggs, leaves the buff and the black in greater quantity for the nesting season plumage. In the winter all three would once more be available.
The fat of the nesting hen is distinctly rich in colour, but in no case that we have seen has it amounted to the orange-coloured fat which is often seen in overfed Pheasants, and quite commonly in Gulls and Terns which have been feeding on red crustaceans. In these birds the orange-red fat or oil, tints not merely the fat beneath the skin, but even the white feathers of the breast and body often present a very beautiful rosy flush.
The whole question of pigment production and pigment distribution, intimately connected as it is with the question of the excretion of waste products and the deposition of fat, both in health and in disease, has not reached a stage which admits of dogmatic statement upon the subject of pattern change in feathers without moult.
One recognised method of changing a colour-pattern in feathers without moult is to be seen in the male of the familiar House Sparrow, which produces a handsome jet-black cravat in the breeding season, where before was a nondescript greyish throat; and this it does by the simple process of shedding the grey ends of the feathers, leaving the blacker parts exposed. This method is common among birds, but the Red Grouse has been credited with changing in situ the colour and pattern of the flank feathers. Now, with still less reason as it seems, the cock bird has been credited by Mr Millais with achieving his summer or breeding plumage "for the most part by repigmentation and pattern change of most of the winter feathers below the neck."
This view cannot be upheld physiologically, and there is much to support the contention that the feathers which are believed to effect this change of pattern without moult are actually new growing feathers. This can readily be shown by the demonstration of their unshed sheaths. The misleading birds are again in this case the cocks which have been too sick to shed the previous "autumn plumage," and so are still struggling, with increasing success as the food improves, to produce a "winter plumage," which they should, and would in health, have achieved in October.
That the cock bird should moult the feathers of the legs and feet between March 30th and June 17th is no longer difficult to understand when the prevalence of Strongylosis is fully grasped. No bird is safe from the nematode infestment, and we are led to think that the majority of cock birds are so badly infested that they are forced to defer the autumn moult which should precede that of the previous winter. It is therefore obvious that between March and June there will be every stage of good or bad leg and foot-feathering between the newly acquired thick, white winter stocking of the sick cock, and the naked featherless clean moulted leg and foot of the really healthy male bird in June. In July, again, the healthy cock bird will be found beginning to produce white feather tips over the legs and feet.
In July the general appearance of the healthy cock is much lighter in colour-tone, and much more broken and mottled in pattern-character than July. that of the same bird in the winter. The claws are in many cases now ready to be shed, and the primaries, secondaries, and tail feathers are in moult. Some six or eight new clean-grown primaries are often to be found in July, and the long tail coverts are broad-barred buff and black.
In August the cock Grouse has, of course, the appearance of full summer August. or autumn plumage, but it requires very little examination to see that he has already begun to put on feathers of the winter plumage. He now rapidly sheds the old feathers of the last winter's plumage which remained throughout the summer upon his breast and abdomen, and replaces them with the exceedingly handsome narrow cross-barred red or brown or blackish feathers of the coming winter plumage. There is no second moult or replacement of these feathers of the breast and abdomen in the cock. Once in the year is enough for this special area, and the feathers that "carry through" are wholly of the winter plumage. They are often broadly tipped with white. The chin feathers which survived with those of the breast and abdomen are now also replaced by new ones. It is noticeable that in the Ptarmigan it is also the white feathering of the chin and of the breast and belly, as well as of the wings and tail, which is changed once only in the year, exactly as with the winter plumage of the Grouse. It suggests that these two plumages are analogous in each species.
The plumage changes in the Ptarmigan are, strange to say, quite different to the chancres in the Grouse. The Ptarmigan has three distinct moults and plumages in the year. The Red Grouse has but two.
In August, as has been said, the cock Red Grouse has begun to put on his winter plumage. The feathers of the breast and abdomen are full of sheaths and sheath-scurf, the growth of these feathers being very rapid and often scarcely noticeable. On the rump, back, and to a less extent on the shoulders, new rich red-brown feathers finely marked with black lines are showing here and there. Primaries, secondaries, tail feathers, and coverts are now replaced by new and blackish feathers with perfect and unbroken outlines. Even a few new rich copper-coloured feathers are appearing as isolated touches of bright colour amongst the faded broad-barred autumn feathers of the upper breast. The feet and legs are bare, save where new white feather tips are just appearing through the skin, and the claws of all the healthy birds are being shed (Pl. xiii., Figs. 3, 4, 5, 6).
In September the chin and throat of the cock Grouse are a mixture of many pale autumn feathers much worn and faded, and a few new September. copper-red ones. Most of the frayed "autumn plumage" feathers are now falling out. The breast and abdomen, wings and tails, are clothed with altogether new feathers, while the head and neck, back, shoulders, rump, and coverts of the tail are in a transition state, the "autumn" feathers frayed and bleached at the tips, contrasting with the new rich chestnut and darker brownish winter feathers with their fine black transverse markings. The feathers of the legs and feet of healthy birds are rapidly growing to form thick, white stockings for the winter. Bare legs in September are a sign of belated moult or, in other words, a sign of sickness.
In October, for the first time since the preceding winter, the red and black varieties of Red Grouse become once more conspicuously distinct. This October result is due to the new growth of fully pigmented feathers, either red or black, upon the under surface of the body. The upper neck is rapidly becoming copper-red. The chin and throat still show a proportion of the faded buff "autumn" feathers among the red, the former looking spotty and pale. On the back the new chestnut and black feathers are rapidly replacing the faded autumn feathers. Some perfectly healthy cocks still look as if in "autumn plumage," while others, on the contrary, have nearly completed their winter dress. The legs and feet are thickly covered with white feathers, and the nails are uniformly small, as the old claws have all been shed. Their growth, however, is extremely rapid.
In November and December the cock Grouse drops most of the remaining "autumn plumage." By the end of the latter month his moult is complete, November
December but on the neck and back a greater or lesser number of these autumn feathers are retained till the following summer.
The most striking characteristics of the winter plumage are the rich copper-coloured neck and throat, and, in the darker varieties which are common in the Scottish Highlands, the contrasting blackness of the upper breast and abdomen often broadly flecked with pure white tips.
Amongst the cocks there are several well-defined and easily recognised varieties, which seem to have a certain regularity of distribution geographically. These will be considered below.
It must not be forgotten that, owing to innumerable efforts, which have been more or less successfully made from time to time, to transfer Red Grouse from one part of the country to another, the distinction of local variations has become a thing of the past, and is now impossible except upon a very limited scale. The attempt, however, can be made, and the number of specimens in the Committee's collection of Red Grouse skins makes it possible to arrive at some conclusions.
- Reprinted from the Proceedings of the Zoological Society of London, 1910.
- (1)"Annals and Magazine of Natural History" (6), xii., July 1893, pp. 62–65; (2) "Catalogue of the Birds in the British Museum," vol. xxii. November 1893, pp. 36–38; (3) "Annals of Scottish Natural History," July 1894, pp. 129–140, Pl. v. and vi.
- "Handbook to the Game Birds," p. 28. (Allen's Naturalists' Library). London: W. H. Allen & Co., Ltd., 1895.
- In lit., "British Birds," for April 1910, vol. iii. p. 352. London: Witherly & Co.
- The whole chapter deals with the Red Grouse (Lagopus scoticus Lath.). The terms "blak Red Grouse" and "buff-spotted or white-spotted Red Grouse" must not be confused with similar terms for other species of Grouse.
- "Natural History of British Game Birds," p. 40.