Removing rats on Ile aux Aigrettes: walking the lines

By Leanna Racine and Tara Imlay, Mauritian Wildlife Foundation

Day 1 – Setting the poison grid
Our alarms go off and we slip out of our bunks. Its 5:30 in the morning and we have 394 bait stations to place. With additional help from other staff from Mauritian Wildlife Foundation and the National Parks and Conservation Service, the reptile team sort everyone into eight groups. Each group is armed with small cardboard boxes, a stapler, permanent marker, notebook and poison. We set off with compass and map in hand to find bait stations. We are quick to discover that finding our stations is A LOT easier said than done even with each point made accessible. Most of the time was spent using a machete to further clear the paths through dense vegetation (usually with lots of thorns) and locate the pegs that indicate corners of the 12.5 x 12.5 m grid covering Ile aux Aigrettes. Poison was placed at every second grid peg, laying down a 25 x 25 m poison grid across the island.

Being the intimidating team that we are, we often felt that our presence was scaring off the grid pegs. However, once a grid peg was located we stopped to fold the box and staple in the flaps. We quickly discovered that our stapler was of substandard quality and had to be fixed after every staple. After placing 8 cubes of poison (40 grams) in each box and a yellow piece of flagging tape overhead, we set off to find the next station.

The island quickly heats up and by mid-morning we were hot, sweaty and dreaming of jumping into the sea. We had just used the machete to cut through the densest part of the island, known as The Hole-y Land. This area is full of thorns that hook into your skin, dense shrubs and deep holes in the ground from old coral. We left this area with more than a few battle scars. We still had about half our poison to place, but thought it was a good time for a rest.

After lunch we headed back out. We were feeling a little more energetic and decided to start with the hardest part. Back to The Hole-y Land. We seemed to get through it faster this time and we were soon comfortably walking through Ebony forest. Although more pleasant to walk through, ferns covering grid pegs made navigation difficult, often standing directly over them asking each other where it could be. Despite a little meandering, we found all our stations and we were finished up at 2 pm. In total our team set out 39 poison stations, a small part of the 394 poison stations that were set in total. Without the extra help from the extra staff it would have been a much longer and more difficult, if not impossible, day.

Day 2 – Checking bait stations
Alarms go off at 5:30, again, small groans and we roll out of bed. We have to check all the poison stations today and our team has been reduced to just the five reptile team members. We divided the island into sections, one for each of us. Equipped with a compass and a map for finding pegs and extra poison to replace any that has been taken we set off.

The first peg takes the most time to find, but the little bits of yellow flagging tape we set up yesterday help to direct our attention. Then walk east to the next one. We get into a groove pretty quickly. Find the peg, locate the box, count the number of poison cubes left, check for rat bite marks and any invertebrates eating the bait, replace missing poison and move on. Most stations are covered in ants, but we also see the occasional cockroach, crab or snail. The biggest offenders of bait loss are crabs and introduced giant African land snails. Although they can consume much of the bait they are not poisoned by it. Those found eating the bait are placed into a bag and removed from the island to try and limit the amount of poison entering the ecosystem and affecting non-target species, such as the endemic Telfair’s skinks that love to eat the invasive land snails.

Things seemed to be going well, but about an hour in it begins to drizzle….then light rain…then heavy rain. Our clothes are soaked, but we are more worried about getting our notebooks wet. Bushes, rucksacks and plastic bags were all used as shields to keep the books dry and when that stopped working we just found shelter and waited out the rain. It is meant to be the start of the driest period of the year and rain in such quantity is very unusual. The rain was creating other problems too as the boxes containing the poison are made of cardboard and may have to be replaced. Only two stations showed obvious signs of rats today, but we are hopeful that with time more rat signs will be apparent.

Day 3
5:30 am. It’s still raining. We found blue rat faeces today, indicating that rats have been eating the bait, which contains blue dye. Seeing blue faeces is very encouraging, because it means that the rats are being poisoned.

Day 4
5:30 am. Not surprising, it’s still raining. We pull on clothes still damp (and now quite smelly) from the last 2 days of rain. We found a lot more blue rat faeces today. Clearly the rats are really taking the bait! Most of our lovely cardboard boxes that were set up earlier in the week are now falling apart and being propped open with small sticks and rocks. They will have to be replaced soon.

Day 5
No rain this morning, but we have several large dark clouds hovering overhead and small showers throughout the day. We found more blue rat faeces today and we are beginning to have an idea of where the rats are distributed across the island. Once it stops raining we will replace the boxes at each bait station and place more bait stations in areas where we see signs of rats.