Invasive mammals

Rats: a little rodent causing a big problem!

Black rats were introduced to the Chagos islands many years ago by passing ships and have had disastrous impacts on the islands. They breed like rabbits and will eat anything they can find - including bird eggs. On islands where rats are bountiful, the number of ground nesting birds have dropped dramatically. Birds are unlikely to return to these islands and the native hardwood trees struggle to grow as the rats also eat their seeds.

Rats as an invasive species

An invasive species is a plant or animal that isn’t native to a location and has spread, causing damage to the environment. After habitat destruction, invasive species are recognised as the second most severe threat to biodiversity. In Chagos, rats have been the biggest invaders.


35 of the Archipelago’s 55 islands are infested with rats, removing them from the islands should allow the ecosystem to begin to recover, increasing biodiversity and the number of naturally occurring species like seabirds, turtles and hardwood trees.

Rat eradication in Chagos

Removing rats from the islands is a tough job, as they are everywhere! However, that is just what scientists are trying to do, but where do you start?! First the island is mapped out and lines are laid out 25m apart, dividing the island into sections. Rat poison is placed along these lines to ensure the whole island is covered and no rats are missed! This task can be harder than it sounds as the centre of the island is covered in dense coconut palms, fallen trees and over-grown Scaevola bushes. There is no guarantee all the rats will take the poison, so this process must be repeated several times.