No birds in the nets this morning and in the afternoon we would be heading to basecamp but we had the morning free so, over breakfast, we had to think of a plan. One of our assignments for the field trip was to make a video relating to the rainforest. We decided to do ours on the importance of beetles to the tropical ecosystem which is such a fascinating subject as beetles fill so many different roles! You have the ones which pollinate the flowers to help the forest grow; beetles that eat rotting wood and vegetable matter, eat animal dung and the beetles which eat dead animals all help release nutrients into the soil adding to the vitally important fertile topsoil (Day 2); beetles that are food for many other animals including the forest people; and finally beetles that bring in money from ecotourism such as fireflies! Inordinately important.

On the table in front of me sat the incredible violin beetle from last night in its handmade palace full of food and places to hide. This gave me an idea. On our first night walk we wandered past a large log which was hollow all the way through and I could sort of remember where it was. Grabbing my camera and the beetle, my group and I set off up the steep valley side slipping on mud and hauling ourselves up with vines. After about 15 minutes of scrambling, some group members were beginning to question the very existence of this log and my encouraging shouts were beginning to fall on deaf ears. As only two of us (David and I) had actually seen this log and its potential, other members of the group quite soon gave up hope and took the safe option of heading back to camp (probably quite sensibly). Cameraman David and I soldiered on and miraculously came across some other members of camp hornbill who had gone on a walk. Persuading one of the guides to come with us instead and lead us to the log, we split off and carried on through the jungle. After another 15 minutes of walking (but with more direction this time) we arrived.

Inspired by George McGavin’s wonderful presenting in Lost Land of the Volcano (absolutely one of my favourite programmes ever as the living in the jungle finding new animals and plants is what I have always wanted to do) we decided that I should crawl through the log to see what I would find.

Suitably drenched in sweat I got in front of the camera and did a quick intro piece before, to our guides incredulity, I proceeded to dive into the log. The rotting wood had created a 5cm thick sludge at the bottom of the tube and on this walked a lot of giant wood ants Camponotus gigas. I did know that these ants are very docile but the sight of their big mandibles right against my nose was a little disconcerting. But then to see them exploring the log was very interesting. They feed almost exclusively on honeydew and so I presume they were just exploring. Luckily they were quite happy to get out of the way of the great lumbering creature that had decided to invade the log.

Further into the log however, I looked at the roof and came face to face with a truly huge female swimming huntsman spider Heteropoda natans guarding her large white egg sac. If I attempted to worm past her I would have certainly knocked her off, something I didn’t want to do. The spiders put so much energy into caring for their young having an idiotic human disturb her would be the last thing she would want! However, I did get the chance to get a good look at her. What is really interesting is that the only other time I saw these spiders was when we were on a river walk and they were hunting. This log was right at the top of a hill meaning this female would have had to migrate up from the river, find the log and form her egg sac a long distance away from her normal riverside habitat. The log must provide a safe environment for her to live in while her spiderlings develop safe from predators. The spider must be quite inhibited by the large egg sac and I don’t think she will feed while she is caring for her children and so finding a good place to sit is vital. What was most exciting was that I consistently observed this behaviour from this species of huntsman over the coming days – any female with eggs was always found in a rotten log near the top of a hill!

Squirming backwards out of the log (carefully shooing any remaining ants out of the way) I emerged incredibly muddy. There was one more shot we wanted to get though and that was of our temporary pet: the violin beetle. Crawling into the log from the top I looked about me and ‘found’ the beetle! Very excitedly we filmed a brief section on the beetle’s life history before letting it go on its way.

Squelching back down the track into camp it was very nearly time to walk to Base Camp. Shouldering our heavy packs, we tramped along the path in a long winding trail. Arriving still completely caked in mud I attempted to wash the worst of it off in the river.

We very briefly met some of the other groups and had two minutes of excited conversations abut what we had all seen before we went off to different camps again. We set up our mosquito nets in the true luxury of a building before heading back to the river's beach to learn about how Borneo’s geography affects the diversity of freshwater fish.

 

Intriguingly the fish species in rivers on the eastern side of Borneo’s mountain range shows much higher endemism (the amount of species present found nowhere else in the world) than the rivers on the western side.

10,000 years ago during the last ice age a land bridge was present between western Borneo, Java and Sumatra forming a landmass called Sundaland. A large river system ran through the centre of this land and rivers from the western side of Borneo’s mountain range flowed into it. This allowed fish living in these rivers to move freely through the freshwater of the large river and up any other tributary they wished. On the eastern side of the mountains it is a very different story however. Off the coast of eastern Borneo is a very deep oceanic feature called the Makassar trench. This separates the Eurasian tectonic plate from the Australasian one and is vital in explaining Alfred Russel Wallace’s Wallace line. Because of this trench all rivers from the eastern side of the mountains ran into the sea and so any freshwater fish in the rivers were truly isolated from each other and have been for many millions of years. This isolation has led to many new endemic species occurring, some with super narrow home ranges of just a single river in some species with poor dispersal capabilities.

All of this makes this area of Borneo an incredibly exciting place to be interested in fish. My fish knowledge is very poor but luckily we had Prof. Frank who knows a huge amount about the local fish species and has found multiple new species from this very river!

First, however, we needed to know how to catch them. With a weighted throw net, we all stood on the water’s edge and attempted to spin the net in such a way that it opened just above the surface with the opening as wide as possible which was a lot harder than it looked when it was being demonstrated. By some fluke I managed it on my first go and even caught a fish! Knowing that things wouldn’t get much better I quickly passed it on to the next person and retreated smugly.

As night fell we headed up river in very heavy rainfall. We were armed with torches and hand nets to catch fish. We were all of course hoping to catch a massive catfish or eel but some of the smaller fish were equally as impressive. There is one called Nematobramis everetti which I think is my favourite. Its dorsal and anal fin (the fin near its bottom (of course)) are very close to the tail and this gives it a large surface area allowing the fish to propel itself out of the water to catch insects!! The fish also has large pectoral fins to help it with this. It spends a lot of its time looking up from the surface of the water and so cannot keep watch for predators below. To get round this problem the fish has two long barbels (string like strands emerging from around its mouth packed with sensory organs) to detect and movement from below. Another fish in the same family (Cyprinidae) has a very different life history. It is called Garra borneensis and will sit at the bottom of fast flowing sections stuck to rocks with a suction pad on its modified lower lip. It spends its time rasping off algae, eyes looking up for any predators.

I of course got distracted somewhat from the fish by all the other life about. A truly beautiful Dolomedes sp. raft spider was sat on the surface on the hunt for small insects and maybe fish (and frogs as we found out in Sungai Wain forest). Excitingly I think this is an undescribed species as I haven’t been able to find any names online and it looks quite different to other Dolomedes I have seen so far. On the river’s edge was a wonderful white orb of a flower, seemingly glowing in the darkness. This flower is especially adapted to bloom at night to attract nocturnal pollinators such as moths and bats (and the nocturnal bee Xylocopa myops – see day 3).

Wading further up river we heard tell that previous day’s groups had seen a pit viper just round the corner and so Ted and I moved forward with purpose. We were hopeful as pit vipers generally stay in one place for multiple days at a time. Heartbreakingly the snake had pushed off tonight so we turned and splashed sadly back down river, listening to the unobtainable horned frogs honking far up the banks. Although we cheered up very quickly when we found a Malayan bent-toed gecko on a mossy log, a very sleepy young Bornean anglehead lizard on a rock in the centre of the stream, a wolf spider carrying all of her children on her back and a crab carrying all of hers underneath!

Back in camp we went through the fish we caught and discussed all their different life history adaptations. Very tired I was getting into bed before noticing some of the incredible moths that had gathered around the lights!

A shout from Ted outside as he had caught a very large purple frog with yellow speckles! A very beautiful animal and we were sure it must be a new species for the trip. However, it turned out to be the rare female morph of the brown tree toad! Interestingly this morph is the most common where we are potentially meaning that this population is fairly isolated in the valley.

We only have one night at basecamp before we head to camp waterfall tomorrow so up early to make the most of it.

Wandering through the jungle

Catharsius sp. of dung beetle

Crawling through the log, camera in hand

Big female swimming huntsman Heteropoda natans

Emerging from the log and being pleased about the Violin beetle

Sketch of the original Sundaland land mass and the Wallace line.

Frank demonstrating how to throw the fish net.

Rough sketch of the Nematobramis everetti fish.

Dolomedes sp. of spider

Nocturnal floweer

Bornean anglehead lizard

Malayan Bent-toed gecko

Wolf spider with young 

Crab with young

Amazing moth

Brown tree toad female

Day 5: Log crawling, back to Base Camp and endemic fish.

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