Red Grouse
From Wikipedia, the free encyclopedia
[Photo] Red Grouse (Lagopus lagopus scoticus) in Peak District National Park. Source: Flickr (http://www.flickr.com/photos/roger/1943212/). Date December 5, 2004. Author Roger Butterfield (http://www.flickr.com/people/roger/) from Sheffield, UK.
The Red Grouse (Lagopus lagopus scoticus) is a medium sized bird of the grouse family which is found in heather moorland in Great Britain and Ireland. It is usually classified as a subspecies of the Willow Grouse but is sometimes considered to be a separate species Lagopus scoticus.
Description
The Red Grouse is differentiated from the Willow Grouse and Ptarmigan by its plumage being reddish brown and not having a white winter plumage. The tail is black and the legs are white. There are white stripes on the underwing and red combs over the eye. Females are less reddish than the males and have less conspicuous combs. Young birds are duller and lack the red combs.
Birds in Ireland are sometimes thought to belong to a separate subspecies L. l. hibernicus. They are slightly paler than those in Britain and the females have yellower plumage with more finely barred underparts. This may be an adaptation to camouflage them in moorland with higher grass and sedge content and less heather.
It is identified by its chut!chut!chut!chut!chut!chuttt.... call, or the 'Goback, goback, goback" vocalisation. The wings make a whirring sound when the bird is disturbed from a resting place.
Grouse populations display periodic cycling, where the population builds up to very high densities only to crash a few years later, and then recover. The main driver of this cyclic pattern is thought to be the parasitic nematode worm Trichostrongylus tenuis.
However, in his book, V. C. Wynne-Edwards suggests that the primary reason for mortality in grouse population is Homeostasis depending largely on food availability and that the 'Grouse disease', due to the parasitic worm Trichostrongylus tenuis is a mistaken diagnosis of the after effects of social exclusion.
Distribution and habitat
The Red Grouse is endemic to the British Isles; it has developed in isolation from other subspecies of the Willow Grouse which are widespread in northern parts of Eurasia and North America.
It is found across most parts of Scotland, including Orkney, Shetland and most of the Outer Hebrides. They are only absent from urban areas, such as the central belt, the flatter areas of the north-east and around Fife.
In Wales there are strong populations in places but their range has retracted. They are now largely absent from the far south, their main strongholds being Snowdonia, the Brecon Beacons and the Cambrian Mountains. There are reports of Welsh birds crossing the Bristol Channel to Exmoor.
In England it is mainly found in the north - places such as the Lake District, Northumberland, County Durham, much of Yorkshire, the Pennines and the Peak District, as far south as the Staffordshire Moorlands. There is an isolated introduced population on Dartmoor, and overspill Welsh birds visit the Shropshire Hills such as Long Mynd, where they breed. The Exmoor population would now appear to be extinct, with the last birds sighted as recently as 2005. An introduced population in Suffolk died out by the early 20th century, though a population on Cannock Chase in Staffordshire lasted longer.
In Ireland it is found locally in most parts of the country.
Its typical habitat is upland heather moors away from trees. It can also be found in some low-lying bogs and birds may visit farmland during hard weather.
The British population is estimated at about 250,000 pairs with around 1-5,000 pairs in Ireland. Numbers have declined in recent years and birds are now absent in areas where they were once common. Reasons for the decline include loss of heather due to overgrazing, creation of new conifer plantations and a decline in the number of upland gamekeepers. Some predators such as the Hen Harrier feed on grouse and there is ongoing controversy as to what effect these have on grouse numbers.
Red Grouse have been introduced to the Hautes Fagnes region of Belgium but the population there died out in the early 1970s.
Reproduction and diet
The birds begin to form pairs during the autumn and males become increasingly territorial as winter progresses. The nest is a shallow scrape up to 20cm across which is lined with vegetation. About six to nine eggs are laid, mainly during April and May. They are oval, glossy and pale yellow with dark brown blotches. The eggs are incubated for 19 to 25 days, the chicks can fly after 12 to 13 days after hatching and are fully grown after 30 to 35 days.
The Red Grouse is herbivorous and feeds mainly on the shoots, seeds and flowers of heather. It will also feed on berries, cereal crops and sometimes insects.
The Red Grouse and man
The Red Grouse is considered a game bird and is shot in large numbers during the shooting season which traditionally starts on the 12th of August, known as the Glorious Twelfth.
Shooting can take the form of 'walked up' (where shooters walk across the moor to flush grouse and take a shot) or 'driven' (where grouse are driven, often in large numbers by 'beaters' towards the guns who are hiding behind a line of 'butts'). Many moors are intensively managed to increase the density of grouse. Areas of heather are subjected to controlled burning, this allows fresh young shoots to regenerate which are favoured by the grouse. Extensive predator control is a feature of grouse moor management, foxes, stoats and crows are usually heavily controlled on grouse moors.
Rarely, protected species such as raptors can also fall foul of illegal control, however this is a controversial topic and the extent to which it occurs on grouse moors is hotly contested betwen conservation groups and shooting interests, it is never the less a topic that generates a lot of media attention in relation to grouse moors and shooting.
In recent decades the practice of using of medicated grit and direct dosing of birds against an endoparasite the strongyle worm or Threadworm (Thrichostrongylus tenius) has become part of the management regime on many moors.
Scientific study
Due to their economic and social importance and some interesting aspects of their biology, red grouse have been widely studied. They were the subject of some of the earliest syudies of population biology in birds, as detailed in The Grouse in Health and in Disease By Lord Lovat in 1911. Since the mid 20th century they have been subject to ongoing study by many organisations and indiviuals. Much work has been conducted by the Institute of Terrestrial Ecology in the eastern Cairngorms, and by the Game Conservancy Trust in the Central Highlands. There are a wide range of research activities still going on today and a wealth of published literature exists on all aspects of grouse biology.
The Red Grouse is widely known as the logo of The Famous Grouse whisky and an animated bird is a character in a series of its adverts. The Red Grouse is also the emblem of the journal British Birds.
Strongyle Worm or Threadworm (Thrichostrongylus tenius)
This endoparacite causes a condition often called strongylosis or ‘grouse disease’ and which can be the cause of regular crashes in grouse populations. When the adult worm burrows into the caeca walls it causes a lot of damage and internal bleeding which in itself is harmful to the grouse. The worms ultimately reduce the digestive efficiency thus affecting the condition of the grouse.
The eggs of the strongyle worm found in the caecal droppings of Red Grouse, hatch out into a microscopic larvae stage. Living within the dropping they feed off bacteria and organic matter they develop through two moults reaching their third larval stage, ‘L3’. The ‘L3’ larvae is now at its infective stage so it ‘swims’ up heather stalks, on a thin film of liquid, to the young shoots where it is most likely to be ingested by a host. Once in the body of a host they enter one of the two Caecum in the intestine of the host where the larvae develop into adult worms. The adults mate within the caeca and the female can lay over 100 eggs a day which are passed out in the caecal dropping.
The development of the parasite can vary greatly depending on the conditions, namely temperature and humidity. The eggs and larvae can both tolerate periods of low temperature but neither can survive in hot and dry weather. In perfect conditions with high humidity and temperatures exceeding 15 °C most eggs will hatch within 24 hours, compared with at 5 °C where the eggs may take several days to hatch out. The larvae can remain active above 6 °C with relative humidity but when it is colder they halt their development but stay alive. With the climate changing as it is the worms find tolerable conditions for much of the year but they are picked up by grouse at two main periods of the year. The grouse may ingest infective larvae from the heather tips in the summer and early spring. During autumn and winter not all ingested ‘L3’ larvae will develop in to adults, the larvae may begin to moult and temporarily halt their development and attach themselves to the caecum wall, they are said to be in an ‘arrested’ state. The larvae over-winter in the bird’s intestine and in March/April when conditions are more favourable they resume their development.
With some other parasites young birds play host to more of the parasites than adult as the adults develop immunity to the parasites but in the case of the strongyle worm. With age the worm burden in grouse generally increases as and each worm in the intestine of the grouse has to be individually ingested and the adult birds appear to have little resistance to the parasite. The burden of worms is obtained when the birds feed on heather and the young birds feed mainly on insects, for this reason this parasite has little direct bearing on chick survival but can badly affect adults and immature birds.
High worm burdens in grouse can lead to mortality and poor condition leading to easy predation and poor reproduction. The strongyle worm burrows into the caecal mucosa which affects the bird’s ability to control the scent it emits making them particularly susceptible to mammalian predators who hunt using scent. High burden leading to poor condition of the hen grouse may not affect the clutch size but can affect her ability to incubate the eggs or brood the chicks so this parasite may indirectly affect chick mortality.
http://en.wikipedia.org/wiki/Red_Grouse
| The text in this page is based on the copyrighted Wikipedia article shown in above URL. It is used under the GNU Free Documentation License. You may redistribute it, verbatim or modified, providing that you comply with the terms of the GFDL. |
|
