Heavy rain and thunder overnight leaves the air dense with humidity. Mandy, Ross and I are to trek north through the old, overgrown logging trails. We dress and pack accordingly but as we set off, I decide that today I would let them trek with the guides and I would go alone to explore the trails around the camp looking for different species of butterfly to record; butterflies tend to prefer the sunnier glades.

 The camp at Sicundur is situated close to the village and is just on the national park boundary outside the buffer zone, so people are never far away. Even so being so close to the forest has a very unique feeling. The thing I like the most is the sweet fresh smell of earth and vegetation. The air has a cleanliness about it that makes you want to breathe it in slowly and deeply. Every now and then you come across a rich heavy scent, sometimes like Jasmine; sometimes like garlic. I walk and walk enjoying the solitude.

It is amazing how much more you see when you walk alone slowly and quietly aboriginal. I take the Slow Loris trail and then the Elephant Trail and watch how more and more butterflies emerge as the heat from the sun increases. It is surprisingly difficult to photograph butterflies; they are deft and amazingly quick: darts of kingfisher blue, emerald greens and vibrant yellow light up the foliage. When they do settle they tease with their wings shut tight hiding their technicolour coats. Sometimes they unfold and it is time to get that shot. A small black mammal crosses the path in front of me; too quick to identify. A chestnut-bellied Malkoha and a Bronzed Drongo are slightly more obliging but still only fleeting glances to behold: maybe that is the charm of wildlife.

As I walk, I think about the forest and the sounds I can hear from the nearby village. Even in the primary rain forest you get a feeling that man is not far away, the fingers of humanity have an incredibly long reach.

Primary rainforest tends to be determined by a greater abundance of large, thick trees which have been beyond the reach of the loggers. Each large tree is a whole ecosystem in its own right and therefore it is not just a tree that dies when man comes to claim it. The sun is now high and the light is strong.  Happy with my morning’s photography, I head back to camp to greet the others. There is lunch to be enjoyed.

Whilst we are enjoying the tucker the research assistants explain that researchers have found an orangutan. We grab our kit and make our way through the undergrowth to where a mother and her baby sit high in the canopy (unlike the orangutans at Bukit Lawang, truly wild ones like to keep more hidden and much prefer the sanctuary of the highest trees). It is totally different seeing unhabituated animals: these ones are right at the top of a tree on a high cliff over the river; a really beautiful place made more special today by the dark skies, angry sunlight and rumbling distant thunder. It feels wild and magical.

The rainforest is made up of every shade of green, light beams, water droplets, backlit vegetation and a symphony of soundbites. Together it makes a complex orchestra with every creature having its own place and time: as the day rolls on species come and go, morning, lunchtime, afternoon, evening, night time and dawn has its own actors. Mandy and I slowly make our way back to camp. With the thunder getting closer, the forest takes on a primeval feel of humidity, stillness and expectation. The downdraft winds caused by the immense cumulous nimbus above us make the canopies sway. Birds and primates get restless and are on the move; a whiskered tree swift, a serpent eagle, a woodpecker all make their way to safety. A fire snake crosses our path into the undergrowth and an ancient, hollow sound reverberates around us. Inside an enormous palm, another orangutan is cracking open and eating the fruit. We smile as the hollow sound breaks his cover.

The river calls us as soon as our feet are back in camp. I stay in the cool water until my skin starts to shrivel and goose bumps cover my surface. I enjoy feeling cold. With the sun going down, it is time for tea and for getting ready for our 8am departure the next morning. Tomorrow we drive six hours back to Medan and then fly to Banda Aceh for the official part of this Sumatran project.

We take our last night-time exploration into the forest once again armed with our spot lights, head torches and cameras: a night activity is full of surprises and we are hopeful and expectant as this is our last evening. Ross and I take the Slow Loris trail. We actually see very little until we encounter an enormous, ancient tree, saved from the loggers only because of the fact that it leans heavily to one side. Here we discover a blue and black gecko, a spider the size of my hand, and the largest ants I have ever seen. Mandy joins us with a night light which instantly reveals sleeping butterflies and a Sumatran pit viper curled up over our heads. Satiated by these finds we head off back to our bed to be ready for our journey tomorrow.

I reflect on all that I have learned here about the forest and about us. Ross and I love the forest but its challenges affect our moods, Mandy, however, is very different. I have never seen anyone so at home in a jungle as Mandy; she seems to be utterly prepared and is totally at one with it. The students who will follow us will hopefully learn to be the same as they will be here for months rather than weeks.