The grouse in health and in disease : being the popular edition of the report of the committee of inquiry on grouse disease / edited by A.S. Leslie ; assited by A.E. Shipley.

  • Great Britain. Committee of Inquiry on Grouse Disease.
Date:
1912
    ment of thirty-six eggs as 45'56 by 31'8 mm., and the average weight of eight eggs as 1'845 g. There is no truth in the belief that disease will follow if the eggs are not well coloured. Very often the uncolouied part of the egg whitens at the same time as the coloured part fades or is washed off, thus making an egg of bad coloui. It is interesting to note that a bird of five years old lays fewer eggs and of a smaller size than a bird of one or two years old. The net yield of the nesting season greatly depends upon the weather in spring ; frost before sitting, snow after hatching, heavy rain following a drought when the birds have nested in low-lying ground liable to submersion, are some of the principal dangers to which early broods are exposed. The eggs also may be lost by a long spell of wet weather, even up to the point of hatching. This is probably not a matter of common occurrence, but in the spring of 1906 the Committee’s field observer saw nest after nest deserted owing to rain. The nests on the low ground fared worst; in some the eggs did not hatch at all, in others only one half, or even fewer, were productive. The parent birds seem to defy the elements at all times, and during the period of incubation the hen will continue to sit upon her eggs apparently oblivious of the fact that a snow- storm is raging which has driven every other living creature off the moor. During such a storm hens are sometimes com- pletely covered with snow as they sit upon the nest, for in hard weather instinct teaches them not to desert the post of duty. Observation of the bird at these times is difficult, for even the most enthusiastic naturalist is not often tempted to explore the higher ranges of the ground in the face of a blinding blizzard. We must to some extent form our conclusions by observation of after-results, and certainly there is little doubt that the effect 1 Dresser’s “ Eggs of the Birds of Europe,” p. 623, PI. lxvii., Fig. 1. London: published for the author at the Office of the Royal Society for the Protection of Birds, 3 Hanover Square, 1905-1910. Nesting in snow.
    Effects of wet. Effects of frost. of a heavy snowfall while the birds are sitting does not appear to produce the number of unhatched clutches of weather- bleached eggs which might be expected. Sometimes, no doubt, matters reach the limit of endurance when, urged by the pangs of hunger, the hen is forced to wander away in search of food and grit, and on her return finds all trace of her nest buried beneath a smooth, white drift. Even in this case all is not lost; the snow fortunately does not lie long in the months of April and May, and in due time she recovers her nest and resumes her domestic duties. It is recorded that in 1908, on a Midlothian moor, a heavy snowfall during laying-time covered the nests to a depth of 9 inches for a period of ten days ; many eggs were lost, some even being laid on the top of the snow ; in many cases the hen bird returned to her nest after the snow had gone and laid more eggs beside those which had been covered—some of these birds hatched out every egg. Other cases have been reported where the eggs were covered with snow for so long that their colouring matter had dis- appeared, and yet they produced a healthy brood. From observations made upon Grouse in captivity it appears that during the period of incubation the hen will often leave her nest for several days at a time, for no apparent reason, and will return again and hatch out the whole clutch—this power of absenting herself without disaster to her eggs must under natural conditions stand her in good stead when the severity of the weather makes the task of incubation unendur- able ; but it is only in the earlier part of the sitting season that her absence is unattended with risk, for once circulation has commenced in the embryo chick the eggs must not be allowed to become cold. Only when the hen is forced to leave the nest on account of heavy rain is there a danger of her deserting the nest permanently—three days of incessant wet will suffice for this. Another danger to which the eggs of Grouse are liable is that of being destroyed by frost while the hen bird is off the nest. This danger is greatest during the period before the
    full clutch has been laid, for after incubation has commenced the hen will not readily leave her nest during frosty weather for any length of time. Before the hen commences to sit she will often cover up the eggs in the nest with twigs of heather, grass and bracken, and this must save many of them from the effects of frost. The Committee has had an exceptionally good opportunity of studying the effects of frost upon the eggs in the spring of 1908, when an extremely severe frost was reported from every district of England, Scotland and Wales. For three days in the third week of April the thermometer registered from 10 to 27 degrees Fahrenheit. The Committee requested its local correspondents to make careful observations on the resulting damage, and the replies received brought to light several interest- ing facts. In general it was stated that the effects of the frost had been disastrous ; but when the evidence came to be analysed the proof seemed strangely incomplete for very few reporters were able to state from personal observations that eggs laid before the frost had failed to hatch. On the other hand, several accurate observers reported that they had marked down eggs so frozen into the materials of the nest that it was not possible to lift them out or to separate them from each other, yet it was afterwards found that these eggs hatched out healthy chicks. On April 13th six Grouse eggs were found in a nest amongst heather when the temperature was 25 degrees of frost—and all six hatched out. On another occasion, when it happened that some Pheasant’s eggs had been laid in a Grouse’s nest, the Pheasant’s eggs were the eggs which failed, while the Grouse’s eggs were successfully hatched. Many observers went so far as to say that unless the frost was sufficiently severe to split the egg there was no danger of their fertility being affected, and of all the gamekeepers to whom the question was put very few could state that they had actually seen a Grouse’s egg split by frost. Actual splitting of the eggs by frost does occur, but it is exceedingly rare when the nest is in its customary position
    in heather. When placed in the open probably the eggs are liable to suffer just as Plover’s eggs did in 1908, and an extra hard frost will sometimes split them. Even very scanty heather-growth retains the warmer air, and so shelters the nest and eggs from frost and winds. Moreover, if sitting has not begun the eggs are generally more or less buried in the material of the nest, so that they are to a great extent protected. The effect of frost upon the eggs of Grouse has been fully discussed in the Committee’s Report, and an analysis is given of the Reports of nearly 200 observers in different parts of the country.1 The deductions to be drawn from this analysis, though negative, are nevertheless of considerable interest. They may be summarised as follows :— 1. Frost in the breeding season does not cause universal destruction to eggs. 2. In some cases it seems to do little or no harm, even though severe. 3. In other cases it seems to do more harm even though relatively less severe. 4. The effects of a hard frost in the breeding season are apt to be exaggerated especially if from any other less obvious cause there happens to be a shortage of young birds in the shooting season. How it happens that eggs in one district seem to be better able to withstand frost than those in other districts must remain a subject for conjecture. Acclimatisation appears a more probable solution than any other, for it is clearly brought out by the Reports that in the more rigorous climates of the north and east the eggs were less effected by frost than in the milder climate of the west. Possibly it may be that in the colder districts instinct teaches the parent birds to take greater pre- cautions, e.g., to nest under the shelter of long heather rather than in open situations. Many cases are recorded of Grouse protecting their eggs from frost by covering them with loose twigs of heather. 1 Vide “The Grouse in Health and in Disease,” First Edition, vol. ii., pp. 132-136.
    Enough has been said to emphasise the statement that the eggs of the Grouse are wonderfully tolerant of adverse weather conditions ; the fact is not sufficiently well recognised, and because occasional losses occur there is a tendency among gamekeepers to put down every failure of stock to some sharp frost or heavy snowfall in the months of April or May. They often do not inquire whether as a matter of fact any eggs were laid at the date when the frost occurred, they seldom support their statement by pointing out nests deserted by the hen after being buried in the snow, they keep the plausible explana- tion ready for use if required, and if the stock after all proves to be up to the average, they feel secretly rather surprised, but say nothing about the adverse conditions in the breeding season, for the excuse may be required the following spring. Thus much valuable evidence is lost owing to the very natural desire of the gamekeeper to prove himself the innocent victim of circumstances. Obviously, if the occasional snowstorms and moderate frosts of a normal April were really responsible for the damage so often attributed to them, it would follow that in a really inclement nesting season, such as occurred in 1908, the effects would have been disastrous throughout the length and breadth of the country. As a matter of fact, the bags in the autumn of that year, though unequal, were well up to, and in some places far above the average ; and even where a shortage of birds was reported the failure could often be traced to other causes than the unfavourable weather-conditions in the spring. While the evidence collected does not confirm the view that snow and frost in the nesting season are extensively destruc- tive to the eggs of Grouse, there is some reason to believe that unfavourable weather, occurring immediately before the date of laying, has an injurious effect upon the breeding powers of the parent birds. In the spring of 1908, for example, it was observed that on many moors birds which had paired, and were about to nest, became packed again on the arrival of frost and snow, and postponed their breeding operations until some