Fersiwn Gymraeg ar gael yma.

Wildlife face threats on a daily basis. One of the most pressing issues (and one of the hardest to control) are non-native invasive species. Today (24 May) marks the start of the Invasive Species Week, which gives us a chance to look at the effect non-native wildlife have on our environment.

What are invasive non-native species?

Invasive non-native species (INNS) is an animal or plant that’s not indigenous to a particular place. Many non-native species take advantage of a new environment and spread, therefore causing damage to the environment. Non-native wildlife, in particular rodents, pose a huge threat to seabird islands across the globe. Let’s take a look at some examples of invasive non-native species and their effects on wildlife in Wales.

New Zealand pygmyweed

New Zealand pygmyweed, which is usually known by its scientific name Crassula helmsii, is an aquatic plant that’s having a major impact on many habitats. It’s a problem on a number of RSPB sites, including our RSPB Conwy reserve in north Wales. The New Zealand pygmyweed smothers the bottom of pools where it’s found and deoxygenates the mud where wading birds like curlew and black tailed godwit feed.

Rhododendron ponticum

It may be pretty, but this invasive non-native plant has a significant impact on our native wildlife. Shrubs can grow up to eight metres tall with a base that spreads out, which causes it to block the sunlight from the woodland floor. This denies many woodland flowers with crucial sunlight and makes it harder for young trees to survive. This has a knock-on effect on the everything. For example, insects are less abundant, which ultimately affects birds such as pied flycatcher and redstart.

Seabird colonies

However, there is some good news. The Celtic Rainforests Wales project is working hard to get rid of rhododendron from some of our most precious areas of woodlands. This of course takes time and careful planning and some good old-fashioned manual labour.

It’s not only invasive non-native plants that are affecting our wildlife. There are some animals that pose a massive threat. One striking example is rodents on seabird colonies across the globe. When rats and mice manage to reach islands (often as stowaways from boats and ships) they cause havoc by predating on eggs and chicks. This has proved to be true on some of the islands off the coast of Wales. Important colonies of puffins on Ramsey Island and Ynys Seiriol (Puffin Island) suffered huge losses because of rat infestation. Both islands are now rat-free, which will hopefully give a chance for puffins to nest safely once again.

One project looking specifically at this issue here in the UK is Biosecurity for LIFE. It’s aim is to implement biosecurity measures for the UK’s seabird islands. The project works with a wide range of stakeholders to raise awareness of the threat invasive non-native predators have on seabird islands. Here in Wales, RSPB’s managed the Skerries off the coast of Anglesey and Grassholm Island in Pembrokeshire (both managed by RSPB Cymru) come under the project, as well Ynys Enlli, Ynys Seiriol, Skokholm and Skomer Islands.

This problem is not likely to go away, especially with climate change making it easier for non-native species to establish in new areas. But it can be dealt with. The best solution would be to prevent non-native wildlife from reaching, and when it does, act swiftly to ensure that our fragile habitats remain unthreatened. To find out more about this issue, follow this link.


Cover: Rhododendron ponticum 

Second: Removing rhododendron ponticum to protect native oak trees in the Celtic Rainforest project area

Third: On some islands, puffins have suffered from rat predation, but with successful eradication, we now hope for their return.