Most Unwanted: Brown rat
Rattus norvegicus
Habitat: Terrestrial
Threat: Threatens protected species
Status: Established
This species is very common throughout Ireland. It is recognised as a devastating invasive species throughout most of its global introduced range due to the impact on agriculture and on native species, sometimes causing or contributing to the extinction of species.
What is it?
The brown rat has brown fur on its back and grey fur on its belly. It is only one of two rat species in Ireland. It can be distinguished from the black rat by relatively smaller eyes and ears which are finely furred compared with the almost hairless ears of the black rat.
Impact
Both species of rats present in Ireland are known to impact on native flora and fauna. The effects these animals have maybe greater on island habitats. These species have been observed to attack and kill chicks, and adult birds, and take eggs from nest sites. Globally, these two species of rats have lead to the decline, local extinction and/or total extinction of bird and other species through predation and competition. The black rat has been described to attack and kill at least 39 bird species, while the brown rat has been recorded predating on at least 53 species. Evidence of predation of predation of small birds on islands is difficult to obtain, therefore this number is likely to be much greater. Arthropods, snails, amphibians and reptiles are generally not as well studied as bird species, and few data is available on the impacts of rats on these organisms, but again there is little doubt that the number of impacted species is very large.
Invasive rats have impacts on plant communities too. These impacts on isolated island ecosystems are extremely important and of concern to conservation managers and enthusiasts alike. Rats are omnivorous, and as well as animal species they are known to eat leaves, seeds, flowers, bark and stems of many species, some of which are endanger of extinction due to their isolation on island ecosystems and lack of adaptations to the new predator. Rats are also known to prevent the regeneration of woodlands by damaging young saplings and adult trees.
The brown rat has out-competed the invasive black rat species on mainland Ireland.
Where is it from?
With a possible origin of North East China, this species has benefited greatly by allying itself closely to man. This species is now present in most parts of the world.
Where are they in Ireland?
Brown rats are widespread on the mainland and are present on an unknown number of offshore islands. There they reduce the reproductive success of ground nesting birds. There is still the risk of spread to other unimpacted islands.
How did it get here?
This species can stow away on freight containers and ships.
How are they spreading in Ireland
Self propelled. They are a highly mobile species and can swim.
Stow away on both large and small vessels.
What you can do
Prevent further spread to offshore islands by keeping boats free of rats.
Use rat guards on mooring lines, where appropriate.Report all sightings.
