The brown rat (Rattus norvegicus) is an incredibly adaptable animal; it can be found almost anywhere in the UK, including our nature reserve. All it needs is shelter and food.
It has grey-brown fur, a pointed nose, large, bare ears and a long, scaly tail; it is much bigger than any mouse species. Water voles are similar in size and colour but are chubbier with a much rounder face, small ears that are buried in their fur, and a furry tail.
 brown rat (Rattus norvegicus)  water vole (Arvicola amphibius)
Brown rats are omnivorous, eating pretty much anything: fruit and seeds, insects, birds’ eggs, even small mammals, as well as the food we humans store for ourselves and our livestock and, of course, the enormous amount of food we throw away. As human populations have grown, brown rat populations have grown with us and while various estimates of the UK’s rat population run from 8 million to 80 million, nobody questions that they thrive best in our cities and towns where they are close to humans.
Despite their scientific name, which translates as Norwegian rat, the brown rat comes originally from central Asia. Today, they can be found in every country, on every continent of the world except Antarctica. Travelling along trade routes, particularly shipping routes, they had found their way to Eastern Europe by the early eighteenth century and to Britain by 1720; at the beginning of the 19th century, they had been identified in every European country.
 black rat (Rattus rattus)  brown rat raiding a bird table, an important source of food for urban rats.
The brown rat has almost entirely displaced and replaced the black rat (Rattus rattus), which was another alien species of Muridae imported into Britain along earlier trade routes , aboard Roman ships. The black rat is now classed as one of our rarest mammals with a population of little more than 1,500, while the brown rat is believed to be our most common mammalian species.
The few species that are able to exploit the modern human environment are clever, adaptable omnivores that frequently earn our displeasure. Rather than treat them as pests, we should admire them; they may well outlast us.