Continuing with the Scotland theme, today’s blog update is about grouse, the wildest group of British gamebirds (not in the party sense, unfortunately – they just typically shun human contact). This one’s pretty long, so grab yourself a cuppa while there’s still time.
There are four species of grouse native to the UK: red and black grouse (which are found throughout Scotland, Wales and northern England in upland areas), and ptarmigan and capercaillie (both restricted to limited areas of Scotland). Like the majority of organisms, these birds face a number of threats to their continued persistence. I’ve included the RSPB’s latest population estimates with each grouse, so that when I say ‘rare’ you know just how rare I mean.
Red grouse [230,000 pairs]
When Scotland’s landscape is mentioned, the most common image that springs to mind is a sweeping vista of open heather moorland, flush with purple flowers at the height of summer. The most characteristic bird of this landscape is, without doubt, the red grouse, Lagopus lagopus scotica. A distinct subspecies (or perhaps sister-species, depending on which taxonomy you trust) of the willow ptarmigan found across the rest of Europe, this pretty russet gamebird is unmistakeable given good views, and synonymous with heather moorland. The main reason for this, of course, is the historical and current popularity of driven grouse shooting, for which red grouse is practically the only target. To ensure profitability, and an enjoyable day for hunters, grouse moor owners (or more often, the gamekeepers they employ) use various methods to make the moorland highly suitable for the birds, unnaturally increasing their population densities.
The most typical form this management takes is heather burning. Red grouse feed primarily on the tender, young shoots of heather (mostly Calluna vulgaris, but also some Erica species), but require older, shrubbier heather to nest beneath. A cycle of burning heather, then leaving it to regrow for several years, ensures a mixture of ages on a grouse moor, improving the habitat for the birds. Across Scotland, the bare, black and grey scars of burnt heather litter the hillsides. While this is great news for the grouse, allowing their populations to boom, it’s generally pretty bad for other creatures. Compared to the surrounding, unburnt heather, recently-burnt areas have greatly reduced invertebrate diversity, which has knock-on impacts for the organisms that feed on them, like wheatears and many other passerines.
Grouse management has one other, major impact: the persecution of other animals. Hares are trapped and disposed of, to prevent them competing with the grouse for food. Deer are shot to reduce the chances of ticks and other ectoparasites spreading to the grouse and reducing their fitness. Corvids, mustelids and foxes are all trapped to reduce their depredations. But the most obvious, and by far the largest impact, has been on birds of prey. All raptors are legally protected in the UK, but illegal persecution is still widespread, and the vast majority is concentrated on grouse moors, where many satellite-tagged birds mysteriously vanish. The birds are usually baited with poisoned carcasses, although more inhumane methods are used out of the public eye, which often cause hours or days of suffering. Golden eagle, peregrine falcon, buzzard, sparrowhawk and hen harrier have all suffered severe population declines and range contractions; red kite and goshawk have been driven to extinction in Scotland . But that’s a whole other can of worms, and a subject for another blog post.
Black grouse [<5,100 males]
Though similar in size and shape to red grouse, and utilising similar habitats, the black grouse (Tetrao tetrix) is very different in a number of ways. While red grouse show very little sexual dimorphism (the red eye wattles of the male being the only difference visible to non-experts), the male black grouse is a lustrous blue-black with white underwings and tail coverts, while the female is barred brown (though still with white underwings, the most reliable ID characteristic in the field). In terms of behaviour, the two grouse are very different. Black grouse prefer to dwell in mid-altitude birch and rowan woodlands with a fairly open canopy, where they feed and roost; they only make their way onto open moors to ingest grit (which helps break down the plant matter in their gizzards), and in spring, to lek. Similar to peacocks, this involves a group of males assembling in an open area and displaying alongside each other. Females easily locate the group and weigh up the benefits of potential partners, before quickly mating and leaving, with males remaining to mate again.
Unfortunately for black grouse, this dependence on two habitats has made them particularly vulnerable to poor habitat management. On the one hand, heather burning for red grouse does maintain the availability of open areas for the birds to lek in, but it also prevents saplings from growing into the adult trees which black grouse also require. Sheep grazing, the other major use for moorlands in the UK, also reduces tree recruitment. Meanwhile, established woodlands go unmanaged, and as the trees age and the canopy closes, the habitat becomes unsuitable for black grouse. These pressures have contributed to the black grouse’s disappearance from upland areas of southern England, such as Exmoor. They are now mostly restricted to high-elevation areas far from human disturbance, where the cold and windy weather keeps birch stands from becoming too thick.
Ptarmigan [2,000-15,000 pairs]
The ptarmigan (or rock ptarmigan as it’s known in continental Europe), Lagopus muta, is one of Britain’s most unique birds. I touched on it in last week’s update, but I’ll recap anyway. The ptarmigan is the only British bird to change colour throughout the year, trading its stone-like grey summer plumage for a thick, pure-white winter coat. The only similar changes are found in mountain hare and stoat, both of which share the extreme upland habitats favoured by the ptarmigan. And ice age relic, this dumpy little grouse is the hardiest of the UK’s species.
Because of its preference for colder areas, where its unique adaptations allow it to outcompete other birds, the ptarmigan is nowadays found only in extreme upland Scotland, where it patrols the windswept heathland on the tops of plateaus and high peaks. As always, evolving such a degree of niche specialisation is a knife that cuts both ways. While the ptarmigan escapes competition from the more generalist red grouse, which is restricted to lower altitudes, it is also placed at high risk from climate change. Increasing annual temperatures push the ptarmigan further upwards through a number of factors, including the uphill range expansion of unfavourable habitats (heather moorlands and birch woodlands), possible competitors (i.e. red grouse), and extra predators (mostly red foxes, but also weasels and other mustelids). Additionally, a pure-white ptarmigan on a snow-free mountain top is something of a target for aerial predators, like peregrine falcons, so the reduction in snowfall also presents something of a problem. Although the ptarmigan is found across northern Europe, Siberia, Canada, and some more southern mountain ranges (namely the Pyrenees, Alps, and Himalayas), it would be a shame to lose such a beautiful bird, and the glacial legacy it represents.
Capercaillie [800-1,900 birds]
The capercaillie, Tetrao urogallus, is the rarest grouse species in the UK, and perhaps the most enigmatic. A huge grouse, the capercaillie shows extreme sexual dimorphism, with the black males up to twice the size of the brown females, easily reaching five kilos. Similar to black grouse, capercaillies have a lek system of mating, with the males fanning out their tails and producing a ‘song’ composed of a series of popping clicks. The capercaillie used to be hunted for trophies and meat, though never on the scale of red grouse – however, having a naturally low population, this drove the species to extinction in the UK in the late 1700s. While this may have been a unique subspecies, no data exists to verify this; the capercaillies currently resident in Scotland were introduced from Swedish stock in 1837. By the 1970s the population was estimated at 20,000 – but has since crashed dramatically, with fewer than 10% that number of birds remaining, and the species again seems to be on track for extinction.
There are a number of reasons behind this, but similar to ptarmigan, the primary cause of the capercaillie’s decline is its specialisation. This large grouse lives exclusively in Caledonian pine woodlands, eating bilberry shoots and other vegetation, where it receives no competition from other birds. However, large populations of sheep and deer can easily reduce its food sources. Additionally, the pine forests it inhabits are now one of the most severely fragmented habitats in the UK, with only a fraction of the original extent remaining, and large gaps between fragments. Unable to fly far, or for a long time, capercaillies have been split into numerous, tiny subpopulations where they still remain, with maybe a few dozen in the largest patches. Attempts to link up forest patches are being undertaken, and may go some way to slowing this incredible bird’s decline.
So far, we’ve discussed the problems particular to each grouse. However, if one issue stretches across all four species, it is that of fence collisions. All grouse have fairly stubby wings, meaning that they have poor manoeuvrability in the air, flying fast and close to the ground to avoid aerial predators. However, this puts them directly in the path of the wire-link deer and livestock fences that crisscross almost all habitats, except the high-altitude plateaus which the ptarmigan inhabits in summer. Collisions with fences are usually fatal, or result in damage to the wings, breast and head which quickly proves deadly, either through internal haemorrhaging, infection, or inability to escape predators or adverse weather. This is such a common occurrence that counting the number of carcasses along fences is a technique sometimes used to quantify grouse populations, with easily more than 50% of capercaillies dying in fence collisions, and similar numbers of the other species.
Fortunately, in this case, there is an obvious and easy solution – making the fences visible to the grouse, which has a similar effect to the practice of tying bright ribbons to long fishing lines, allowing diving seabirds to avoid entanglement. If the grouse can see the fence coming, they can adjust their flight course to take them over and back down, reducing mortality significantly. Some landowners do this by wrapping wire fences in luminous orange plastic mesh, which certainly does the job, but is visible from afar and quickly degrades when exposed to cold, wet, and sunny conditions. A less intrusive, more long-lived approach, is to slot hazel splints vertically into the fence every fifty centimetres or so. The pale wood does the same job of alerting the grouse, but blends into the environment far better, and biodegrades more slowly. Hopefully, we can encourage such effective solutions to the other problems facing our four grouse species.
Until next time, when I’ll be diving into the sticky subject of raptor persecution,
Cover image credit to Charlie Hedley.