Watch out for alien species

AS I type, I’m keeping one eye on a cat lurking in the bushes near a bird feeder outside the window.

The white devil is waiting to pounce on unsuspecting prey.

And while this fine feline would undoubtedly claim Irish heritage, there are countless breeds of cats, both domestic and feral, of dubious pedigree and with origins in various parts of the world.

A killer of massive numbers of birds, the cat is probably our most lethal predator, and is among many creatures listed in up-to-date EU reports on invasive species. Threats posed by such species in Ireland, both animals and plants, have been highlighted for some time and now the European Environment Agency (EEA) says they pose greater risks than previously thought for other forms of life, human health and economies.

There are more than 10,000 alien species in Europe. The rate of new introductions has accelerated and is still increasing. At least 15% of these species are known to have negative effects though some, food crops for instance, can also have huge benefits. Others, however, cause havoc here, notably American mink imported for fur-farming in the 1950s; the American grey squirrel is seen as a risk to our own red squirrel, while pest plants such as Japanese knotweed and the rhododendron have long been with us.

The most common reason species are introduced is for gardening, while others may be brought in for farming, hunting and fishing, or as pets, one report notes. Transport is not always intentional: for example, zebra mussels have stowed away in the ballast water of ships and can end up in rivers and lakes.

Climate change may also play a role in their spread, according to the report, making some areas more favourable to plants and animals originally from elsewhere.

For humans, one of the most dangerous effects of invasive alien species is as a carrier of disease. The Asian tiger mosquito has arrived in Europe and has been linked to more than 20 diseases, including yellow fever.

Cats have been introduced to about 180,000 islands worldwide, and have a significant impact: in Britain alone where they kill an estimated 25m birds annually. Figures for Ireland are probably comparable.

Mink, which escaped or were set free from fur farms decades ago, have adapted well to Irish conditions and have proliferated, with devastating effects on local wildlife, particularly ground-nesting birds.

Hybridisation can also be a problem and Japanese knotweed is a particularly virulent hybrid of two species originating from Asia.