Removing rats on Ile aux Aigrettes: setting the grid

By Rouben Mootoocurpen, Mauritian Wildlife Foundation

Rats have got onto the island of Ile aux Aigrettes, which lies just off the coast of Mauritius. This small island has been restored by MWF as a nature sanctuary and icon of what biodiversity in Mauritius used to be like. But for fragile islands such as this, the introduction of rats can be devastating to native species. In the last post we saw how once the evidence of rats was first seen, the eradication process was started.

As soon as the Giant tortoises where penned we started to clear paths across the island to create a 25x25m grid across the 26ha island. These paths would allow us to place bait stations at 25m intervals so that all the rats on the island are likely to find the bait and eat the poison.

Straight lines were cut along permanent labelled markers/pegs in the ground spaced 12.5m apart. These pegs, which make their own smaller grid across the island are normally used by island staff to record the locations of the animals and plants they work on. Many of these pegs are not accessible or not visible because the vegetation has grown over them since they were first placed. Therefore, the reptile team joined by volunteers and labourers armed with compasses and machetes created narrow paths through areas where the vegetation was too thick to walk through. The team worked from day break to dusk on 12th October and also the following morning to ensure that all lines could be walked or at least scrambled through. This was really hard work, as summer has started, it is the driest part of the year and it gets very hot.

A large area of the island in the east and south has been named the “hole-y land”, because of numerous deep holes that penetrate the sharp and ragged coralline rock, many of which are over 2m deep. Once you are in the hole-y land you need to watch every single step, especially in areas where ferns cover the ground and the holes. This area is also covered in dense patches of thorny and barbed plants. The native Scutia myrtina proved to be the worst with its backward hook shaped thorns that entangle and tear clothes and skin. It is also very springy, so when chopped with a machete it bounces rather than getting cut and entangles your hands and arms.

In most places the paths were not cut as it would have meant cutting endangered plants. In these cases we need to find the best route through by squeezing beneath low branches and over coral rocks, or simply push through the scrub, picking up some thorns on the way. All 394 positions/pegs were located and access to each one was possible, at least with a compass and maybe a little more pruning with a machete through some of the thorny patches.

The next stage was to clearly label each point with a big yellow tag to make them visible from a distance for the team that will lay the poison and then monitor these bait stations.