The other week I attended a conference in Peterborough on non-native birds; species that had become established within Britain, not through natural colonisation but as a direct result of our own actions. Typically, these were birds that had either escaped from captivity and established feral populations, or been deliberately released by those who thought that they would make a good addition to our native fauna. I was presenting a paper on Eagle Owls, looking at the potential impacts of this large predator on other species now that it had established a small breeding population in the north of England.
Some of the introduced species are obvious, notably many of the exotic ducks and geese that have become established over many decades. Species like Canada Goose and Egyptian Goose are now well established and, while seemingly innocuous, bring with them their own problems. Then there are other species, like Ruddy Duck and Ring-necked Parakeet, which give greater cause for concern. Introduced from North America, Ruddy Ducks now breeding in Britain turn up in Spain where they interbreed with the endangered (and native) White-headed Duck, threatening its very survival. Ring-necked Parakeets now have a population numbering many thousands of birds, centred on London and threatening native species which rely on the same types of nest site. Additionally, the parakeets damage the economically valuable horticultural industry with its heartland in Kent.
As well as such obvious and high profile additions to our fauna (and flora – think of Rhododendron, Japanese Knotweed and Buddleia) there are many hundreds of other species that have become established, many of which we think of as native simply because they were introduced such a long time ago. Included within these are creatures like Fallow Deer, Little Owl and Brown Hare, the latter seemingly an Iron Age introduction from Denmark or the Netherlands. Because we tend to think of these species as being native this clouds the issue of what to do about other introduced species. Is it right to wish to eradicate one particular introduction but tolerate another? Purists might argue that any species that has been introduced to a new area by Man should be removed, but what if the species in question has been here for many hundreds of years without any negative impact on our native wildlife? Others might argue that we should accept that such species are here, would be difficult to remove and so we should just learn to live with them.
There are clear cases, however, where an introduced species is a real threat and should be controlled. For example, the eradication of introduced cats, goats, pigs and rats from British Overseas Territories is essential if we are to prevent the extinction of several endemic bird species.