aliens?

thoughts on the spread of non-native species

 

 

 

rabbit in a summer meadow

Take a walk in Epping forest and the surrounding meadows, and you are likely to see two species of mammal : rabbits ( the European rabbit Oryctolagus cuniculus ), and squirrels ( the eastern grey squirrel Sciurus carolinensis ). Occasionally you will see fox and deer. But the rabbit and squirrel are super-abundant, and these two are not native to Britain. The grey squirrel is native to the eastern Unites States, and was introduced as a pet in the19th century. The European rabbit is native to Spain and Portugal, and came to Britain much earlier. It was brought here by the Romans, although the present population may descend from rabbits Normans cultivated after the invasion of 1066.

This week the the grey squirrel has been in the headlines, after Prince Charles said he would like to see the British population completely exterminated.  There are several charges made against the grey squirrel. One is that the native red squirrel ( the Eurasian red squirrel Sciurus vulgaris ) is dying out because of competition from greys. Certainly there are no reds left in Epping Forest. There is a small pocket of reds in the reserve at Formby which I visited last year, on the Isle of Wight, and on the island of Anglesey. But the red squirrel has largely disappeared from England and Wales, and the battle-front between the species is now in Scotland where the reds are still the majority. A cull of grey squirrels is already underway in Scotland, to create a sanctuary for reds.

I quite like the idea of a red squirrel sanctuary. It might be possible to hold the line for the reds by shooting only a small number of competitors, in areas where reds are still the majority. I hope to able to see red squirrels again when I visit Scotland. The picture below was taken in 2008 in Abernethy Forest, an area of ancient Caledonian pine forest. Photographing red squirrels in this magnificent environment was one of the highlights of the year.

hanging on : a red squirrel in Scotland

I am uncomfortable though about a campaign to remove grey squirrels from areas where they are well established, and where reds no longer live. It may be that our native species struggle not just because of other introduced species, but because their natural habitat is being destroyed by humans. Britain was once covered by forests, almost all of which have been felled. There are still a lot of trees but they are mostly in small woods separated by roads and by cultivated land. This mixed environment may suit the adaptable grey squirrel better. We don't seriously intend to restore Britain's natural forest habitat, which could only be done if the human population is massively reduced. So having transformed our environment we will now have to accept that the resident wildlife species will change as well, according to how well they can adapt to the man-made landscape. Some will thrive and others will not.

It is also possible, however, that the grey squirrel will displace the red in all environments. If this is the case, the introduction of the grey is the root cause of the decline of reds, and the case for controlling it is stronger. There is evidence from the United States to throw some light on this. However before talking about the US, it's important to realise that the American red squirrel ( Tamiasciurus hudsonicus ) is a different species from the Eurasian red. The American red ( inset, photographed in Canada ) is a specialist eater of pine cones, whereas the Eurasian red is an omnivore. In the US its range overlaps with that of the eastern grey but there is no evidence that it is being displaced from the northern pine forests, to which is seems to be supremely well adapted.

In the western US, the western grey squirrel (Sciurus griseus) has declined drastically in numbers over the past century. A report by the state of Washington says that habitat destruction has forced the native squirrel into small areas where the population suffers from inbreeding, and numbers may not be sufficient for long term survival. The introduced eastern grey squirrel puts further pressure on the western grey, but there is no suggestion that the eastern grey should be culled. The Americans seem to regard the eastern grey as a species that does well in parks and gardens, but are clear that loss of habitat is the main cause of the decline of the native species. The experience in Washington highlights that we can't just destroy most of a habitat and suppose that squirrels will continue as before with proportionally reduced numbers. The situation is much more complex and sensitive than that.

 

a thriving grey squirrel

So could the Eurasian red squirrel be in danger of extinction? It seems it isn't, according to the IUCN the Eurasian red squirrel is not endangered, being ranked as LC ( least concern ), and the population is spread widely across northern Europe and Russia. However there are some differences in appearance between the British and continental squirrels, ours being a particularly rich red color, so the British are justified in being proud of it.  I hope that calls for extermination of greys are rejected though. We could destroy grey squirrels and then find that the reds can't thrive in the broken woodland that remains here, and that would be a great shame, because all the squirrel species are delightful and deserve our protection.

rabbit's tales

Rabbits have been in Britain for a long time. Rabbit bones were found along with Roman remains at a site in Lynford, Norfolk in 2004. We know that rabbits were highly valued by the Romans, who bred them in an enclosure called a leporarium, so it seems likely they would have brought them to Britain after the invasion of AD43. It's not clear whether these early rabbits survived in the wild. The Norman invaders also brought rabbits ( known as coneys ) and employed warreners to care for them, providing winter feed and protecting them from poachers. They did not multiply in the wild until more recently. It may be that modern patterns of farming have helped by reducing the numbers of predators and clearing forests for crops. I suspect also that some adaptation was needed, since the European rabbit is native to the warmer, drier conditions of southern Europe. Once established though, its ability to multiply rapidly in the wild can soon make it the enemy of farmers.

Australians have become especially hostile to rabbits. A small population released in Victoria in 1859 bred so fast that within 10 years, two million rabbits were being trapped annually. Through the 20th century Australia has waged chemical and biological warfare on the population, culminating in the release of the myxomatosis virus in 1950. The disease spread accidentally to Britain killing 95% of our rabbits. Rabbits have now developed some immunity to myxomatosis. In 1995 the Australian government released a new virus causing Rabbit Haemorrhagic Disease (RHD) which has devastated the rabbit population again. The Australian government says rabbit damage costs $600m annually, which is certainly a lot of money, but this is only about 3% of the total agricultural income of $20bn. It's the nature of farming that a percentage of your crops will be eaten by wild animals, birds and insects. It's estimated that 10% of crops are being eaten by kangaroos in some areas. I suspect that rabbits are a particular focus of anger because they are not a native species. While farmers have a right to protect their crops, I don't like to see indiscriminate killing of the sort produced by myxomatosis, which will destroy animals that are not damaging crops, and even those living in other countries that might be profitably farmed.

The debate over the treatment of a non-native species is particularly one-sided since conservation groups, hoping to return nature to its pre-industrial state, often side against the introduced wildlife. Only the animal welfare campaigners are prepared to help, and I'm coming round to their way of thinking.

 

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