An integral part of the rewilding agenda is that of the release or encouragement of large predators back into environments where they have been absent for a long time. In the European scheme of things, this means Wolves, Lynx, Bears and Wolverines. The British rewilders are a little more modest in their ambitions and will settle for Wolves and Lynx.
Eurasian Lynx (Lynx lynx) (Source: Speakzeasy.Wordpress.com)
The theory behind this ambition is the concept of Keystone species – that is, those top-of-the-food-chain predators that are said to regulate the rest of the food chain by virtue of controlling the numbers of herbivores below them in the food chain. This has a knock-on effect on the vegetation in the habitat and so also regulates all the other species in the habitat, in what is known as a trophic cascade. The rewilders assert, with very little evidence, that the release of large carnivores into the British landscape will correct the many ecological wrongs they they believe have been perpetrated upon Britain since, say, the Middle Ages.
European wolf (Canis lupus) (Source: wolf-wisper305.tripod.com)
This article has been split into two separate blog posts. Part 1 (this post) will concentrate on the effects of historical acts of releasing species, both alien and formerly native, into the UK environment. Part 2 will deal specifically with Lynx and Wolves.
Introductions and re-introductions into the UK
Table 1 is a list of introductions of some of the plants and animals that have been introduced into Britain over the last 150 years or so. It is far from exhaustive – I have mentioned only five plants introduced, when in fact there are many hundreds. Plantsmen and gardeners have been the most prolific of rewilders since the 18th Century. The bulk of the list comprises mostly mammals and birds which have been deliberately or accidentally released into the British landscape. I have assessed whether each of these releases are harmful, benign or beneficial and given a starred rating to the degree to which they may be thought of as harmful. The purpose of the Comments column is self-evident. These are my assessments and could be disputed by enthusiasts for the particular species concerned. There is an official and much more comprehensive list of non-native and invasive species. This is a guide to identification, but little more. Most surprisingly, the Grey Squirrel is missing from this list. The official strategy for dealing with non-native invasive species is here.
Table 1 – List and assessments of principal uncontrolled alien releases into the UK.
|Species Introduced||Harmful or Benign?||Harm Assessment||Comments|
|Wild Boar Sus scrofa||Harmful, but can be considered beneficial in some cases. Technically not alien, as it was native to UK until Medieval times.||**||Damages crops, especially maize, digs up pastures, lawns and playing fields. Potentially dangerous to humans, but attacks are rare. Can cause serious accidents on roads. Thought to help woodland regeneration by disturbing ground, allowing tree seedlings to develop. Population is increasing in density and distribution.|
|Sika Deer Cervus nippon||Seriously Harmful||****||Breeds quickly and overwhelms habitat with very heavy browsing. Population in south Dorset is huge and troublesome to farmers and conservationists, but is being controlled by heavy culling. In Scotland, it interbreeds with native Red Deer and reduces sporting value.|
|Muntjac Muntiacus reevesi||Very Harmful||***||Can reach high densities in woodlands and clear all vegetation below their browse line, thus damaging flora and fauna in native woodlands. Can damage gardens and allotments. Spreading rapidly.|
|Chinese Water Deer Hydropotes inermis||Potentially harmful||*||Habitat of reeds and tall grasses in wet areas has restricted its range in the UK.|
|Fallow Deer Dama dama||Generally benign||Introduced by the Romans and possibly again by the Normans. Does not appear to be increasing as rapidly as many other deer species; and does not seem to be as damaging.|
|Edible Dormouse Glis glis||Benign||Currently limited in its range around Hertfordshire. Can damage orchards.|
|Coypu Myocastor coypus||Seriously harmful||****||Severely damages wetlands by extensive burrowing and feeding on surrounding vegetation including roots and rhizomes. Reedbeds are destroyed and converted to open water. Damage is intensified because they feed continuously throughout the winter and so vegetation is unable to recover. Eradicated from the UK by 1989 after an intensive trapping campaign.|
|Grey Squirrel Sciurus caroliensis||Seriously harmful||****||Has completely displaced the native Red Squirrel within its range and is increasing that range across the UK. Bark stripping habits are particularly damaging to native trees as well as commercial forestry.|
|American Mink Neovison vison||Seriously harmful||****||Responsible for elimination of Water Voles from many rivers and waterways. Moorhens, Coots, Kingfishers, ducklings, waders and all other waterside dwelling species are all subject to heavy predation by Mink. They can also cause considerable damage to poultry.|
|Signal Crayfish Pacifastacus leniusculus||Seriously harmful||****||Carrier of Crayfish Plague which wipes out all native Crayfish in the vicinity.|
|Rose-Ringed Parakeet Psittacula krameri||Nuisance||*||Confined to mostly urban areas in London and the south-east of England. Defra have designated them as pests and they can be shot without a licence.|
|Monk Parakeet Myiopssitta monachus||Nuisance||*||Mostly confined to urban areas in SE England. Can damage electricity substations and are potentially to native wildlife. Defra has instituted a cull to attempt to eradicate the wild population. Can be shot without a licence.|
|Eurasian Eagle Owl Bubo bubo||Potentially harmful||**||Whether it has been introduced or arrived naturally is unclear. UK population is small and scattered but appears to be naturalising and increasing. Occupies similar ecological niche to Buzzard, but is much bigger and more aggressive. Can take medium sized domestic animals.|
|Ruddy Duck Oxyura jamaicensis||Very harmful||***||North American close relative to European White-Headed Duck Oxyura leucocephala whose aggressive mating techniques meant it would rapidly hybridise with the European species. A Defra instituted cull has reduced the UK population down to less than 200 individuals. It is hoped to eradicate it completely.|
|Japanese Knotweed Fallopia japonica||Seriously harmful||****||Highly invasive and difficult to eradicate with herbicides. Creates dense stands which eliminate native species. Rhizomes can extend to 3 metres deep. Disposal of material from excavated Knotweed is classified as controlled waste. May cause difficulty in obtaining a mortgage to buy any property upon which Japanese Knotweed is present.|
|Himalayan Balsam Impatiens glandulifera||Very harmful||***||Invasive weed, naturalised in many parts of the UK. Aggressive seed dispersal and high nectar content allows it to create dense stands which out-compete native species.|
|Spanish Bluebell Hyacinthoides hispanica||Very harmful||***||Hybridises with the native Hyacinthoides non-scripta and also shades the native Bluebell out. Vigorous and spreading into many parts of Britain.|
|Giant Hogweed Heracleum mantegazzianum||Seriously harmful||****||The sap causes phototoxicity of the skin, inducing a serious rash, inflammation, blisters and black or purplish scars which can last many years. It should only be handled with protective clothing. Ecologically, it forms dense stands and thereby excludes and smothers native plants.|
|Rhododendron Rhododendron ponticum||Seriously harmful||****||Highly invasive and grows rapidly to an almost complete canopy, thereby shading out native species of plants and animals. Causes land abandonment in extreme cases.|
The above is just the more obvious species in terms of size and impact. It should be noted that very few are classified as “Benign”, and the rest are harmful to some degree. 63% are either “very harmful” or “seriously harmful”, None of them have been ecologically beneficial to the environment in which they live. All of the above have been introduced by humans without any thought that they may damage the natural or man-made environment. Some, like wild Boar or Mink, are escapes from farms or where they have been deliberately released by animal rights activists. So far, no large mammal carnivores have been released into the British countryside.
By contrast to the unofficial releases, there have been a number of releases which have been officially sanctioned and done under carefully controlled conditions by various NGOs such as the RSPB. Figure 2 below is a list and an assessment:
Table 2 – Recent controlled and officially approved re-introductions.
|Species Re-introduced||Harmful or Benign?||Comments|
|European Beaver Castor fiber||Benign? Said to be beneficial by beaver enthusiasts.||So far, only subject to small reintroductions in limited areas. Said to improve water retention on a landscape scale to help flood prevention, as well as improving biodiversity. But some are opposed to beavers because of potential adverse effects. So far, claims on both sides of the argument are unproven.|
|Reindeer Rangifer tarandus||Benign||Only one small herd in the Cairngorms.|
|Common Crane Grus grus||Benign||Returned naturally to Norfolk in 1978, but numbers have since been supplemented by hand rearing and reintroductions to the Somerset Levels and other places. Population now estimated to be about 160 birds (2016).|
|Great Bustard Otis tarda||Benign||Small population of 50+ hand reared birds plus some wild bred birds on Salisbury Plain.|
|Red Kite Milvus milvus||Whether benign or harmful is completely un-assessed.||Traditionally thought of as a carrion eater, but very wide range of prey means it is harmful to ground nesting birds. Competes with Kestrels Falco tinnunculus and Barn Owls Tyto alba for voles and small mammals. The very small Welsh population has been supplemented by releases of Spanish and German birds in the Midlands and the north of England. Now common in many counties.|
|White Tailed Eagle Halieetus albicilla||Probably harmful to sheep and fish farms.||Reintroduced to north-west Scotland using Norwegian birds. Now nest mostly on Mull and Skye. There is a big reintroduction programme for the east of Scotland, another in Ireland, where it is not at all popular. Estimated to be 106 pairs in Scotland (2015). Food is mainly fish, but also takes carrion, birds of all descriptions, occasional lambs and fish from fish farms.|
Here, the picture is a little better with most being classified as benign. However, Red Kite and White Tailed Eagle are both large raptors and so are also highly effective predators. With that ability also comes their potential capacity for doing harm to human activities such as farming. There is also the capacity for altering the balance of the ecosystem once numbers have increased.
Tables 1 and 2 above suggest that the damaging effects of many of these species have much to do with the interloper competing with native or local species.
Lessons from Kestrels and Buzzards.
The Bird Atlas 2007-11  says this about the Kestrel:
“The breeding range has contracted by 6% since the 1968-72 Breeding Atlas, with losses occurring in south-west and central Wales, in western Scotland and sparingly through the midlands and the north of Ireland. These relatively small losses [in range] conceal a larger population decline: numbers in the UK declined by 32% during 1995-2010…part of an overall decline of 44% since 1970. ….. The abundance change map shows that Kestrels have declined in abundance in many parts of Britain and Ireland…..
Causes of decline are unclear and possibly complex, although agricultural intensification, the impact of second generation rodenticides, damping of the vole cycles and competition have all been proposed. Petty et al (2013) gave good evidence that direct predation by Goshawks had contributed to the decline in Kielder Forest, Northumberland, and Shrubb (2004) considered this likely to be occurring also in Wales.”
The population of Kestrels has declined considerably since 1970. Although the causes are noted as being unclear, there seems to be recognition of competition as a possibility. One possible competitor for the Kestrel is the Buzzard. In contrast with the Kestrel, the Buzzard has increased its range and population density considerably .
The Kestrel is a predator of small mammals, birds and sometimes Dor beetles, depending upon the time of year and locality. In the UK, voles, Wood Mice and shrews form 60-85% of the diet . The Buzzard is a much larger generalist predator and consumes a very wide variety of prey, within certain size and weight limits. They will use different techniques, depending upon what is available within the habitat: perching to scan ground and then planing onto the prey; surprise flights using intervening cover; soaring over the territory; hanging in the wind; hovering; walking on the ground to pick up invertebrates and variants of all of these. Voles and rabbits are important parts of their diet; nidifugous chicks of pheasant, partridge, waders etc are all taken. The list of food items is long and varied .
Consider a Kestrel which has maintained a territory for voles and mice. The arrival of a Buzzard into that territory now puts pressure on the supply of voles. However, the Buzzard will also take many other items, such as rabbits which are outside the size range that can be taken by a Kestrel. The result is that the Kestrel now finds its food supply depleted by a much bigger neighbour. The Buzzard, having reduced the voles, can switch to other forms of prey much more easily than the Kestrel. So the Buzzard survives and the Kestrel either moves or cannot breed because the territory will not support a mate and young Kestrels to fledging. This kind of scenario is fairly typical of many situations where a generalist predator squeezes a specialist predator out of a habitat. This is particularly a problem where the generalist predator is both novel to the habitat and bigger than the specialist. Inevitably, the native specialists suffer the consequences.
The Red Kite is an example of a species which has now built up to sufficient numbers and population densities to act as an additional competitor for resources such as small mammals which have hitherto been the preserve of the Kestrel and Barn Owl. These two species have already come under a good deal of pressure from the Common Buzzard, which is exploiting parts of the same ecological niche. The effects of the addition of the Red Kite into the mix is unknown, principally because the work has not been done to find out. Additionally, changing agricultural methods mean that there are fewer small mammals such as voles, because there is less suitable habitat for them. So the supply of voles is far from being sufficiently elastic to supply the increased demand. In the absence of hard evidence, common sense has to be brought into play – where there is intense competition for limited resources, then it is most likely that the bigger generalist predators will win; and the smaller, more specialised ones will lose. This means that the Kestrels and Barn Owls will lose out to Buzzards and Red Kites.
We know enough about the changes in populations of Buzzards, Red Kites and Kestrels over the years because they are diurnal birds of prey and there are plenty of birders in the country to monitor their numbers. So we can see, at a very superficial level, changes in their respective populations to be able to speculate that there might be some inter-specific competition between them. But when species are more difficult to find or observe, it is often difficult to see what is going on until numbers have reached a point where changes can be seen from casual observation. This can be benign or even positive in some way, but in the instances in Table 1 above, the effects of the alien species are nearly all negative – either in an ecological or in an economic sense, or both.
Lessons from Alien Species already released into Britain.
From all of the above, we can draw several general lessons from releases of alien species into the British landscape. We can also draw lessons from what is known about the expansion or contraction of well known native species such as Buzzards and Kestrels. These can be listed:
- Ad hoc and illegal releases of both plants and animals into the UK have had a very unhappy history of ecological and economic damage. Much of that damage (or harm) has been considerable.
- The history of official re-introductions has been better, but large avian predators are either unknown in their effects (Red Kite), or are known to have some negative economic effects (White Tailed Eagle).
- The reintroductions of Red Kite and White Tailed Eagle are not known to have any beneficial effect upon the ecology of the ecosystems into which they have been released.
- The motivation for the release of large raptors has been based upon aesthetic, cultural and emotional/nostalgic reasons. Or, put another way: they have been released for their own sake and for the pleasure of those who wish to see them.
- Generalist predators are better able to compete with specialist predators, especially when the generalist is able to exploit the specialist niche – disadvantaging the specialist – and then swop prey to other species where the specialist is unable to do so. A bigger generalist may also prey directly upon smaller specialists.
- The effects of an apex predator (e.g. Buzzard or Lynx) often means either competition or direct predation upon meso-predators (e.g. Kestrel or Fox/Badger/Pine Marten/Wildcat). These interactions are often unknown and unpredictable until numbers of the introduced species have reached the point whereby their effects are obvious even to the most cursory examination.
- The ecological harm done by the uncontrolled releases has only become noticeable when numbers of the alien species have built up to a point where, for most of them, it becomes a huge and expensive task to remove them from the landscape. The effects are often only noticed after the situation has reached a point where it is already too late to do anything other than keep the situation under control and prevent further spread. In many cases, even preventing further spread is an uphill battle with serious risks of losing altogether. The Signal Crayfish and Grey Squirrel fall into this category.
In summary, the history of releases into the British landscape has been especially poor. In almost all cases above, the risks to the environment and to agriculture have not been assessed in any way by those who have made the releases. The results have been completely unpredictable and often extremely damaging to everyone.
If the rewilders wish to convince us of the benefits of releasing lynx and Wolves into Britain, then they need a lot of hard evidence to prove their case. So far, they have produced nothing but some poorly expressed ecological theory and a lot of aspirational statements with nothing to back it up.
 Balmer DE, Gillings S, Caffrey BJ, Swann RL, Downie IS and Fuller RJ (2013): Bird Atlas 2007-11: The breeding and wintering birds of Britain and Ireland. Kestrel pp. 316-317. BTO Books, Thetford.
 Cramp S and Simmons KEL (eds) (1979): The Birds of the Western Palearctic, Vol II. Oxford University Press, Oxford.
 Balmer DE, Gillings S, Caffrey BJ, Swann RL, Downie IS and Fuller RJ (2013): Bird Atlas 2007-11: The breeding and wintering birds of Britain and Ireland. Buzzard pp. 308-309. BTO Books, Thetford.