Saturday, 13 October 2012

Galliformes 8: Red Grouse

Red Grouse (summer)
While many species of Galliform bird can be seen in zoos and private collections all over thw world, one group is conspicuous by their near total absence. These are the grouse, the various species of which are the most distinctive terrestrial birds of Arctic and Taiga regions of the northern hemisphere. Often classed as a separate family Tetraonidae, they have many unique dietary and behavioural specialisations, which is why they are much harder to maintain in captivity.

The key feature of grouse is the diet, especially in adults. While chicks feed heavily on insects as with pheasants and partridges, adult grouse are specialists in plant parts which often have a low energy content, such as leaves, catkins, buds and even heather and conifer needles, which practically nothing else can eat. To digest this, they have proportionally large guts and gizzards, and are often fairly large birds themselves. With a heavy “payload” they are not very good fliers for the most part, especially the large males, and tend to prefer to run for cover rather than fly.

In the UK we have four species currently resident. A fifth, the Hazel Hen Tetrastes bonasia, is known from subfossil remains but seems to have become extinct shortly after the end of the last glaciation. Of the surviving species, the largest is the Capercaillie Tetrao urogallus. Somewhat similar, except for the smaller size, is the Black Grouse Tetrao tetrix. Confined to a few mountains in Scotland is one of the most distinctive, the Rock Ptarmigan Lagopus muta, which changes colour to match the snow in the winter.

Hazel Hen
Finally, one of the most economically significant wild birds in Britain is the Red Grouse Lagopus lagopus scoticus. This is an endemic subspecies of the extremely widespread Willow Grouse, which has a circumpolar distribution in tundra with patches of birch and willow. As many as 20 different subspecies have been named, but they are all fairly similar (except for the UK form), and are not considered threatened.

Willow Grouse (Alaskan form)
The British Red Grouse has become a quite distinctive subspecies and in many respects its ecology and behaviour, as well as its appearance, differs from its relatives elsewhere. As far as appearance goes, the most distinctive feature is that it has lost the ability to turn white in winter, as its close relative the Rock Ptarmigan and its continental relatives still do. Another feature is a habitat change, from tundra and taiga woodland to more open, treeless areas.

At what point after the last glaciation (or possibly before) it acquired these distinctive differences is a matter for some debate, but it is now dependent on heather moorland in the north and west of the British Isles. This habitat however, is almost certainly largely, if not entirely, a result of human caused changes following overgrazing, poor land management, and increased rainfall during the Neolithic and Bronze Ages, as early farmers cleared forest over thin soils, resulting in the upland areas of Britain being mostly abandoned.

With a restricted habitat, it was more advantageous for the birds to stay close to where they were born rather than trying to disperse into hostile country, and studies have shown almost all Red Grouse breed within 1km of the nest they were hatched in. This means that the various populations on moorland and now reproductively isolated from each other, especially in England, which may be having an affect on breeding success and disease susceptibility. Red Grouse are prone to large variations in numbers from year to year, and tick-borne viral diseases and nematode worm infestations can cause heavy mortality, especially in chicks.

The other cause of mortality (aside from shooting) is predation, and this is where Red Grouse management can conflict quite seriously with other conservation priorities, especially birds of prey and in particular Hen Harriers. Moorland is favourite habitat for Hen Harriers as well as grouse, and the need for gamekeepers to ensure large grouse populations has led (and still does) to persecution, including shooting and poisoning. There is no doubt that Hen Harriers prey on grouse, as like all predators they take whatever is easiest to catch and no self-respecting bird of prey would ignore an easy to catch meal like a grouse, especially when it has been the beneficiary of land management designed to increase its numbers for shooting concerns. In some cases at least they can reduce grouse numbers to the point at which a shooting estate ceases to be viable, a concern that can have serious economic impacts in areas where there is not much other employment.
Land management for grouse takes the form of careful management of the heather moorland to ensure a plentiful supply of new, young heather growth. This is done by controlled burning, which has to be done at the right time of year and under correct weather conditions to be effective. There also needs to be control of tall trees which provide nesting sites for crows ( a major nest predator), and also other animals on the moor. Sheep carry the vial disease louping ill, which is pread to grouse by sheep ticks and causes up to 80% mortality in grouse chicks. Louping ill was probably introduced into the UK around 800 years ago, but probably did not much affect grouse until the spread of sheep farming in the 18th century. A vaccine exists, but sheep ticks also feed on red deer, another host for the virus, and deer numbers in the UK have greatly increased in recent decades.

As a result of all this, plus the decline in control of generalist predators such as foxes and crows since the 1940’s, grouse numbers shot each year in the UK have fallen by over 80%. Despite this, the population is still doing well as a whole, and any walk on moorland will enable you to see (or more often hear) their distinctive call.

Next week: the Red Grouses’ rarer relative, the Rock Ptarmigan

(images from wikipedia)

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