Defra's own research shows that countless caged pheasants and partridges suffer from painful open sores on their feet caused by the wire mesh floor, as well as wounds caused by aggressive pecking from cage-mates - a direct result of the overcrowding.
As the pheasant shooting season begins today, spare a thought for the 35 million pheasants and red-legged partridges, both non-native species in the UK, that are released onto UK country estates each year .
These are not wild birds who roam freely until killed quickly by a competent shooter. No. They are factory farmed in much the same way as intensively reared chickens.
Yet they are not protected by humane slaughter laws - and many of them will never even be end up on anyone's plate. Most are shot purely for sport, with many wounded and left to suffer.
According to the Department for Food, Environment and Rural Affairs (Defra), virtually all of the red-legged partridges released on UK shooting estates come from breeding birds confined in barren wire mesh cages with less space per bird than an A4 piece of paper, often for their entire life .
An increasing majority of breeding pheasants are now also confined in wire mesh cages for at least three months a year .
EU has banned barren cages - but not for pheasants
European law lays down minimum standards for the protection of animals bred or kept for farming. However, it does not apply to "animals intended for use in competitions, shows, cultural or sporting events or activities." This denies birds farmed for shooting the same welfare protection as birds farmed for food, despite the similar rearing conditions .
In fact, since January 2012 barren cages for egg-laying hens are illegal in the EU. Most caged hens are now kept in colony cages housing 60 to 80 birds, with the space per hen approximately 20% larger than an A4 piece of paper. Nest boxes, litter, perch space and claw-shortening devices must be also provided .
Most people would think this falls short of 'barely adequate', yet game birds fare worse. There are no minimum legal space requirements for caged pheasants and partridges, and enrichment is given only a cursory mention in Defra's voluntary Code of Practice for the Welfare of Gamebirds.
Moreover, these are still semi-wild birds, unlike domesticated chickens, who find confinement highly stressful as evidenced by repeated jump escape behaviour .
Defra's own research shows that countless caged pheasants and partridges suffer from painful open sores on their feet caused by the wire mesh floor, as well as wounds caused by aggressive pecking from cage-mates  - a direct result of the overcrowded conditions.
To reduce the injuries caused by pecking, breeding pheasants have various devices forced into their nostrils which either prevent the beak from closing fully (called 'bits') or block their forward vision (called 'spectacles') .
Rearing for slaughter
Many of the 35 million birds released on UK shooting estates actually start their lives on intensive farms in continental Europe - at least 50% according to Defra . These young birds can spend 20 hours or more crammed inside a crate stacked in the back of a lorry travelling from farm to shoot .
Shooting estates buy young birds from breeding farms and rear them in crowded sheds and pens, releasing them just a few weeks before shooting season begins.
Once released, the birds are encouraged into areas where shooting will take place by the distribution of large grain feeders which are attractive to these captive reared birds.
Millions die on the roads surrounding shooting estates , causing damage to vehicles and distress to motorists.
In addition to providing food for these alien birds, gamekeepers on shooting estates wage a war on native predators such as foxes, magpies, crows and birds of prey to ensure the maximum number of birds are available for paying shooters.
Millions of foxes are shot and snared  - an incredibly cruel and indiscriminate practice that is already outlawed in most of Europe. Countless magpies and crows are lured into cage traps using live decoy birds. Protected birds of prey continue to be shot and poisoned illegally.
Pheasants naturally occur in Asia and red-legged partridges are natives of southern Europe, yet for economic reasons they are exempt from laws governing the release of non-native species. There is widespread concern amongst conservationists that this vast number of alien birds has an adverse impact on native wildlife.
Multiple studies suggest releasing game birds at this density reduces food available for native bird species and damages habitats vital for nesting birds.
Endangered butterfly species, such as the Adonis blue  and pearl-bordered fritillary , are also negatively affected when game birds are released in large numbers as the birds eat their caterpillars and the plants which the caterpillars feed on.
What happens on the day of a shoot is little different to 'canned' hunting - where animals such as lions are tamed and confined in an enclosed area to make killing them easier.
Pheasants and partridges which have been farmed, fed and 'protected' from predators are driven towards paying shooters by employees called beaters. They stomp noisily through woods and shrubs until the scared birds fly out in the direction of the guns. Dozens of birds fly overhead simultaneously while the shooters fire.
Many of the birds, up to 40% according to a former training officer at the British Association for Shooting and Conservation , are wounded not killed. Some are left to die slowly where they fall .
More than 500 birds can be shot on one estate in one day. This is not one for the pot. Most birds are dumped in makeshift pits along with the spent shotgun cartridges. The 'natural', 'free-range' image the shooting industry promotes is simply not true in the great maority of cases.
The Netherlands recognised this in 2002 when it banned the farming and release of birds to be shot. The UK should do the same. The League is calling on the government to ban breeding cages for game birds as they are totally unsuitable for semi-wild species.
We are also demanding an independent inquiry into the commercial shooting industry to examine the welfare and ecological impacts of farming millions of non-native birds simply to be shot for sport.
Dr Toni Shephard is Head of Policy and Research at the League Against Cruel Sports.
- 'Whitewashed - the short and miserable life of game birds' by Toni Shephard.
- View the League's new exposé of the short, unpleasant lives of pheasants.
1. British Association for Shooting and Conservation (2015): 'BASC statement on game bird release numbers'.
2 . Defra (2015): 'Evidence Project Final Report AW1303'.
4 . Farm Animal Welfare Council (2008): 'Opinion on the Welfare of Farmed Gamebirds'.
5 .Compassion In World Farming: 'Welfare of laying hens'.
6. League Against Cruel Sports (2015): 'Cruel Game: the truth behind pheasant shooting'.
7 . Defra (2015) Evidence Project Final Report AW1303.
8 . Game & Wildlife Conservation Trust: 'Effects of spectacles on pheasants'.
9. Defra (2015) Evidence Project Final Report AW1303. Ibid.
10. League Against Cruel Sports (2015): 'Cruel Game: the truth behind pheasant shooting'.
11. Bicknell J., Smart J., Hoccom D., Amar A., Evans A., Walton P., Knott J. (2010) Impacts of non-native gamebird release in the UK: a review. RSPB Research Report Number 40. ISBN: 978-1-905601-26-4.
12. Defra (2012): 'Determining the extent of use and humaneness of snares in England and Wales'.
13. Geoffrey Underwood (2007), former Training and Development Officer for the British Association for Shooting and Conservation, giving evidence at employment tribunal.
14. League Against Cruel Sports (2015): 'Cruel Game: the truth behind pheasant shooting'. Ibid.
15. Callegari S.E., Bonham E., Hoodless A.N., Sage R.B. and Holloway G.J. (2014) Impact of game bird release on the Adonis blue butterfly Polyommatus bellargus (Lepidoptera Lycaenidae) on chalk grassland. European Journal of Wildlife Research 60:781-787.
16. Corke D. (1989) Of pheasants and fritillaries: is predation by pheasants (Phasianus colchicus) a cause of decline in some British butterfly species? British Journal of Entomology and Natural History 2:1-14.