The brown rat is a common, widespread and distinctly unpopular Irish wild animal. They are not native.
The first ones arrived, as stowaways on sailing ships, around 1720 and by 1730 had become a serious pest in Dublin. Before then the only rats in Ireland were black rats.
They are also non-native but arrived much earlier — they were present in early Christian times and are illustrated in the Book of Kells. The Black rat caused the plagues that affected Europe in medieval times. It’s smaller than the brown rat and doesn’t compete well with it, as a result it is probably now extinct in Ireland. Both species originate in east Asia. Brown rats can breed all the year round, though most litters in Ireland are born between March and November.
The number of young varies between three and 10, depending on the size of the mother, and she can produce up to five litters a year. In the absence of predation or human control, populations can increase very rapidly.
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