Sunday 18th July was due to be busy. As part of the Bourn Free project to restore native wildlife to the Bourn Brook, I was scheduled to work on a long stretch of the upper reaches with the Cambridge Conservation Volunteers (CCV). The forecast was for another really hot day. I thought I had better get started early loading up the waders and equipment for the volunteers, and first thing in the morning is always important to check trap alarms from our network of mink rafts as most often mink go into a trap during the night. Co-ordinating the volunteers is an important part of the mink eradication program.

There had been no overnight alarms so preparations for the balsam task were underway when a trap alarm went off on the River Nene near Peterborough. This trap has been silent since we put it in place at the end of May, so this was the first test of the local volunteer network response. Fortunately, Emily Coleman was able to co-ordinate this one while I loaded up – we have four or five local volunteers for this trap, and it is important that only one attends to avoid wasting effort, but of course we must also ensure that someone attends promptly. With it being hot we ideally wanted it checking quickly, it’s not good to leave a trapped animal for long. Who’s up, who has spare time and who can get there first? On this occasion, help was there within 2 hours. The trap was closed but empty; perhaps a passing canoeist or angler had interfered with it, perhaps something small enough to get in and out of the trap had triggered it (we know weasels can do that!) or perhaps it had been jolted by a boat wake or a larger animal jumping on the raft – otter, swan or dog for example. We will never know.

I got all the volunteers into the right pairs of waders and into the right parts of the Bourn Brook when the alarm network went off again, just after 11am. This was in a country park, where again we know kayaks can get to. The raft is well hidden from the public on foot. Once again Emily co-ordinated magnificently, and the site ranger was able to get there within the hour and confirm another closed, empty trap. We are starting to fear the hot summer weather with school holidays approaching! Fortunately, these events are generally scarce but getting two on the same morning was a bit annoying.

The balsam project is starting to take effect in the upper reaches, where we have put in the most concerted efforts. By focussing on the upper reaches we should get to a point where seeds no longer wash down to the lower reaches round Lark Rise Farm. Until we have got to that point, the efforts in the lower reaches will always be compromised by further spread. Keeping the numbers of Himalayan balsam down on the CRT stretch will benefit the native vegetation, but we can’t expect to completely remove it until the upper reaches are free. Our strategy in the upper zone is to go to each section twice, with visits early and late in the season. We work in pairs, for safety, and my role is to ensure that each stretch is completely covered. When we started this part of the brook 1km would take a dozen people all day to clear, but now the number of plants is so low that ten of us cleared over 1km in the morning. Plants were generally in small numbers, one or two per 100m of bank. The hardest part of the task is finding the final one – they can hide in nettle beds, on the top of the bank or in little side channels and the terrain is very difficult to search thoroughly. Hence two visits are so important. Ones that germinate early in good growing conditions will be big and obvious in early summer, but those that are later or in less favourable spots might be only 10cm high on the first visit. Going back in a month’s time they will be over 1m and in flower so we have a second chance to find them before they start to produce seed. Any that we miss will produce hundreds of seeds, with the first ripe seed possible in early August, so it is important to try and find them all. Unfortunately, some seed will survive for two years before it germinates so it can take several years to completely eradicate it, but in the furthest upstream area we are at that point. The map shows how we plan for different pairs to work; when pair 2 and pair 4 meet up, we know that the stretch between them has all been checked.

After lunch, with it being so hot, several of the group decided it was enough for one day, but half of us stayed on for another hour. Much of this area has dense tree cover over it and the water is quite deep in places, so working in waders is not too bad, you can cool off in the deep sections. But walking back to the parking place in full chest waders in the sun is also known as the ‘boil in the bag’ moment!

After we finished, I took the waders back to their storage place and parked the land rover up before going to the allotment to get some food for dinner. While digging my new potatoes the trap alarm system pinged again, this one was on the Bourn Brook, and I was the closest available responder so back to the land rover and down to the brook once more! This time there was something clattering about in the trap though I couldn’t see it clearly at first. I hauled the mink raft onto the bank and took the trap out to find a half-grown mallard duckling! This was the first time I’ve had a duck in one of these traps, and it was a good sign that there have not been any active mink on the brook this summer as duckling is one of their favourite foods. The raft also had a scattering of water vole droppings on the corner so that was further proof of the success of this eradication attempt. Trap reset, I headed home for that meal.

Just after I finished my main course an alarm went off again! This time one in deepest fenland, a lovely nature reserve. It was getting a bit late, just after 8pm, and it would take anyone a good while to get there. We gave the volunteer network a call but no-one had replied by the time I finished my pudding, so I decided it was best to get there before nightfall and set off, it’s a 40 minute drive but the roads were all clear so I got there just after 9pm. It’s a bit of a walk to the raft, then a hack through head-high reeds and nettles trying to avoid walking into the drain itself before getting to the raft which is well and truly hidden from the public! All this exertion against the clock got me into a bit of a sweat. Despite two varieties of insect repellent, I was certainly attracting a great deal of attention from the local mosquito population! Once again, the trap was occupied and this time it was a juvenile Water Rail – a rare waterbird like a small brown moorhen with a long bill. I was very relieved to release it safely back into the wild now rather than having been left in the trap overnight. I took a more leisurely stroll back through the reserve as night fell, with some magical experiences seeing a Long-eared Owl and hearing their young begging calls, also Tawny Owl adult and young were calling, a Grasshopper Warbler was rattling out its distinctive song and a Hobby was catching insects high overhead in the last few rays of light.

I got home tired but satisfied with a good day’s work only to find another trap had pinged off while I was driving home! This one would have to wait for the morning. And fortunately, our local responder was there first thing to release a water vole. We don’t get alarms every day, so to get five in one day was exceptional. The fact that none of them were mink shows that we are getting closer to the point where mink are a thing of the past, and we can finally close up all the traps and let our water voles, water rails and mallards go about their business uninterrupted by our efforts to protect them! But a few days later another trap in the county picked up a mink so we can’t yet let our guard down. It’s not over till the last one has been caught. This is the crucial difference between eradication and managing or controlling numbers; eradication is intensive but has an end point; controlling numbers on a site while there are others at large is an endless task though it may feel like less effort at the time!