Rodent like the brown rat would be the most common of the rodent species found in Ireland, they are variable in both size and colour depending on the habitat in which they live. Adult can grow up-to 28cm in length, females weighing up-to 400 grams while there male counter parts are slightly heavier weighing in at around 500 grams, breeding females can produce up-to 5 litters per annum, and each litter can produce between 1 and 10 pups.
Pregnancy lasts for just over three weeks with pups born naked and blind generally not weighing more than 6 grams. Weaning begins almost immediately after birth and lasts for three weeks with parental care given by the female only. Female brown rats can become pregnant again before the first litter is fully weaned. Typically the smaller the litter size than the faster the pups will grow.
Young brown rats reach full sexual maturity after only three months allowing for rapid increases in population numbers if suitable conditions are provided, however the mortality rate of some rural populations can reach as high as 90% in their first year.
This species of rat can be found living in commercial and industrial buildings, on landfills, in sewer systems, along inland waterways such as urban canals, on rural farms and along Ireland's coasts. Brown rats occupying urban habitats usually nest in cellars, attics or on the ground floor.