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

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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

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