Brown rat

Rattus norvegicus


Common Names: Brown rat, common rat, Norway rat


Description: 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.


Origin and Distribution: 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.


Impacts: 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.


How did it get here? This species can stow away on freight containers and ships


Where is it found 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.


See the National Invasive Species Database for more information on the distribution of this species in Ireland.


Prevent Spread

Invasive Species Ireland

Invasive Species Ireland