Author and bird guide Dominic Couzens
As the autumn takes shape and turns into winter in the next few months, spare a thought for the Capercaillie
asks us to spare a thought for the poor old Capercaillie during the cold winter months.
YOU AND I might feel gloomy at the prospect of short days and long, cold nights to come, but at least most of us can resort to the fireside and spend the evening watching TV when it’s freezing outside. The Capercaillie obviously has no such prospects and indeed, it has a severe trial ahead, a trial not just of chill and darkness but also of exceptional tedium. The only consolation, not that the big bird knows it, is that it doesn’t have to endure months of The X-factor.
To get an idea of the Capercaillie’s prospects of extraordinary dullness, take this standout quotation from the section on the grouse family in Handbook of Birds of the World, Volume 2: “It has long been known… that there are birds that spend almost all winter in a single pine tree, even though their browsing may leave the tree conspicuously damaged…” Seriously? A bird as big as a Capercaillie might spend months on end without coming down from a single tree? Apparently so. Think about this for a minute. A large bird spends October to March in a few cubic metres of pine tree canopy, without going anywhere else much. This is a bird that can run and fly and do all the things birds should be doing. And yet, at least in the middle months of winter, it stays put. It doesn’t hibernate, and as far as is known it doesn’t go into any kind of metabolic rate lowering and torpor. It just perches on the branches of a tree and does practically nothing, for hour after hour, day after day.
A six-month pine needle diet
One thing that the bird does not need to worry about, though, is nutrition. The quotation above mentions that Capercaillies browse in the tree and, indeed, that is what they do. Their diet, for as many as six months of the year, consists of nothing except for pine needles. Again, this is quite mind-boggling. Now pine needles are very low in nutritive value, but they are also super-abundant. So the bird doesn’t even experience the inherent stimulation of looking for food; it is there at the wing-tips, so to speak. A study in south-east Norway, on a latitude just a little to the north of Scotland, found that Capercaillies show extraordinarily low levels of activity. The average total daily activity between November and April was only three hours out of 24, and males only spent two hours being active in December and January. Females spent longer feeding on average, with 2.7 hours of activity during those same months, but they are smaller birds and liable to lose heat at a slightly higher rate than the males, the latter being twice the weight. There is a marked change in April, when females take advantage of snowmelt to feed on new growth on the ground, and may feed for four hours or more. It still isn’t much. Throughout the winter it seems that the birds always have an afternoon feeding peak. In the coldest months, they avoid activity in the chill of the morning.
Bacteria and grit
Grouse are very unusual in that they typically feed on leaves and other parts of plants that are known not to be particularly nutritious. They have very long guts, and within their alimentary canal, notably in the caecum, there is a rich bacterial flora: the bird equivalent of a ruminant’s stomach. These bacteria break down plant cellulose and release the nutrients and even generate a little extra internal heat. The grouse also ingest large quantities of small stones to help break down the needles in the crop, sometimes as many as a thousand. They do this mainly in the autumn. Apparently, some birds do die if they cannot obtain the grit they need. Another study in Norway compared some of the chemical properties of the needles of trees that were either browsed or ignored by Capercaillies. They found that favoured trees contained higher concentrations of nitrogen than un-browsed trees, and that the needles of ignored trees held high resin content. The ideal tree has a high nitrogen content and low resin, and perfect trees are presumably scarce. The birds also prefer old, taller trees with wide crowns and large branches under the canopy, and they make sure that there are flight escape routes away from the branches, especially when roosting. Yet another study found that trees positioned with one escape route down a forest aisle were less attractive than trees with two or more potential flyways. Females preferred more open forest than males. The birds usually roost halfway out along the branch. This means they are protected from above by the canopy and are likely to detect ground predators, such as martens, by swaying of the branch as the latter attempt to stalk along it. It seems that the microclimate of the roosting tree is not as important as the security it offers. Capercaillies sometimes share roosting trees, so the very best ones are evidently also at a premium. Unexpectedly, perhaps, they come down from the branches heavier and in better condition, having thrived on a ‘deprivation diet’. The Capercaillies descend to a timetable of good eating and breeding madness. At last, in snow-free patches, they eat flower-buds and catkins, and these must taste fantastic after the monotony of all those pine needles. As is well known, the males then begin to display against each other at leks every morning. Suddenly a bird that lived in a world of bleak tedium can revel in the challenge and novelty. The only problem is that males, at least, now find themselves displaying each dawn to a critical audience of rival males and choosy females. The watching panel can discard them at will, and often do. It’s cruel, and it’s a bit like a summer X-factor, everybody’s worst nightmare.
ÇTREE GROUSE Capercaillies are the most arboreal of our grouse
SIZE DIMORPHISM Male Capercaillies are much bigger than females, so lose less heat in the cold of winter
NEEDLED Capers may spend the whole winter feeding on pine needles of a single tree