2 posts in the category

Invasive species

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Squirrels in Britain: the red v. the grey

Grey squirrel in the Royal Botanic Garden Edinburgh (25th of June 2008).

As you most likely already know, the red squirrel (Sciurus vulgaris) is Britain's native squirrel. But over the last century or so it has been largely superceded by the grey squirrel (Sciurus carolinensis), a native of North America. The greys outcompete the reds, which are then displaced from their territories. According to the Forestry Commission:

Greys can feed more efficiently [than reds] in broadleaved woodlands and can survive at densities of up to 8 per hectare. The density of reds is up to 1 per hectare in broadleaved woodland but can be as low as 0.1 per hectare in coniferous woodland.

The grey squirrel also hosts the ‘squirrel pox’ virus, by which it is rarely affected. But the disease can be passed on to reds to whom it is fatal. The range of red squirrels in Britain is therefore much smaller today than in the good old days before the greys were introduced.

From the point of view of British ecologists and conservationists the reds are the goodies and the greys are the baddies. Of course, individual grey squirrels don't know that they are invasive aliens causing the extinction of a fellow species. They are just doing what comes naturally. But the undesirability of the grey squirrel isn’t limited to its interactions with the reds; greys are predators of bird nests and strip the bark from trees, leading to poorer trees and poorer woodland owners.

Red squirrel at Cluny House Gardens, Aberfeldy (18th of November 2011).

So what is to be done? Land managers with a vested interest in reducing grey squirrel numbers (whether for the benefit of red squirrels, trees, or other wildlife) have a few options. Greys can be trapped, poisoned or shot. The Forestry Commission uses poisoned bait, but doesn’t advocate large-scale culls:

Eradication is not a feasible or desirable option given current methods. Worldwide, the record on eradicating small successful introduced mammals is very poor with research showing that low-level widespread culling has no impact on either grey squirrel numbers or upon damage to trees and priority species. As such it is ineffective and a waste of resources.

Even with new methods and unlimited resources, a successful eradication policy would require the total support of the public. Evidence suggests that a substantial proportion of the public would not support a grey squirrel eradication policy. This policy aims to create a balanced approach to wildlife conservation: controlling grey squirrel populations at a level which does not threaten our native woodlands and priority species.

So, member of the public… would you support a grey squirrel eradication policy? I would. The benefits are greater than one might first suspect: see these stories from the Guardian (quoted) and the BBC!

At Ridley's Fish and Game shop in Corbridge, Northumberland, the owner David Ridley says he has sold 1,000 [grey squirrels] - at £3.50 a squirrel - since he tested the market at the beginning of the year.


Simpson likens the taste to wild boar. Ridley thinks it is more a cross between duck and lamb. 'It's moist and sweet because, basically, its diet has been berries and nuts,' he said.

Both believe its new-found popularity is partly due to its green credentials. 'People like the fact it is wild meat, low in fat and local - so no food miles,' says Simpson. Ridley reckons that patriotism also plays a part: 'Eat a grey and save a red. That's the message.'


'A large squirrel would be enough for one-and-a-half people. The public really are being drawn to it. I think that it's because it is being perceived as a healthy meat. Southern fried squirrel is good. And tandoori style works. It is especially tasty fricasséed with Cornish cream and walnuts. But the one everyone seems to like is the Cornish squirrel pasty.'

Grey squirrel in the Royal Botanic Garden Edinburgh (25th of June 2008).

Posted in Invasive species + Pests and diseases

Rhododendron ponticum L. - enemy of the woodland

Rhododendron ponticum is a non-native evergreen shrub species existing in the British Isles as an alien. It is an extremely important species for two main reasons. Firstly, it is superbly adapted to thrive in many British habitats; particularly woodland, of both coniferous and broad-leaved varieties. R. ponticum is ‘thoroughly naturalised’ in many woodlands, particularly on sandy podzolic soils. This prolific invader is a substantial ecological menace to the natural woodland flora and fauna of the British woodland. Its foliage is so thick that it casts a dense shadow that prevents light reaching other woodland flowers. Further, R. ponticum contains poisonous chemicals, thus inhibiting predation, and deters competition allelopathically via the secretion of acids. Secondly, it is a host plant of Phytophthora ramorum, the pathogen behind Sudden Oak Death. For these reasons, R. ponticum must be managed in order to curb its negative effects upon the natural ecology of the British Isles. Unfortunately, R. ponticum is particularly difficult to eradicate; its waxy leaves render herbicides generally impotent, it produces vast quantities of seed, and it requires much labour to chop down or uproot, it being a large plant.

The above passage is an abridged version of the introduction to an essay I am writing as part of my degree in Ecological Science at the University of Edinburgh. I just hope that people realise, if they didn't already, the tremendous damage being done to our woodlands by rhododendrons.

R. ponticum inflorescence.

Posted in Invasive species + Pests and diseases

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