Nietoperek Revisited

This post was written by Andrew Harrington

You might remember last year Denise wrote an article on this blog about the Nietoperek bat reserve in Poland, which is one of the largest bat hibernation sites in Europe. At the time, she was writing about a trip we went along on to take part in a survey of the underground tunnel system at Nietoperek for signs of pine and stone martens which go underground looking for easy pickings among the thousands of bats which hibernate here, usually ones which have neglected to perch high up enough on the walls of the tunnels to avoid becoming dinner.

Brown long-eared bat with its ears curled up under its wings in hibernation.

Brown long-eared bat with its ears curled up under its wings in hibernation.

More recently, I was kindly invited back to Nietoperek bat reserve by Henry Schofield of the Vincent Wildlife Trust in the UK and Tomasz Kokurevicz of Wroclaw University to take part in the annual count of the hibernating bats, so I found myself driving in a car in early January 2013 on the icy road from Berlin with a group of “pine marten people” from Waterford Institute of Technology who were returning to carry out a repeat survey of the tunnels to look for marten scats. So, I thought you might be interested to know how exactly do you figure out that you have 40,000 bats in the basement and decided to write this blog on my experiences over that weekend.

We arrived in Swiebodzin about 2 hours after leaving Berlin and decided to stop off to get supplies before heading to our base camp for the weekend’s surveying. We dropped by the local Tesco, which was easy enough to find because it’s on the ring road right next to the biggest statue of Jesus Christ in the entire world- yep, it’s even bigger than the one in Rio de Janeiro (seriously). Or at least that’s the locals say, and they’re understandably very proud of it despite the somewhat incongruous place they put it in.

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The largest statue of Jesus Christ in the world!

We then continued onto the tiny village of Wysoka about 10 kilometres north of Swiebodzin, hidden in the middle of the expansive, flat, forested landscape of western Poland. When we arrived at our little hotel, our hostess Yola complained about all the rain they’d been getting this winter and how abnormal it was (try living in Ireland, I thought). However, the rain was turning to snow just as we arrived and rapidly the whole village had a covering of several inches of it. As our small group had arrived early, we headed out into the surrounding countryside to enjoy the snow and to explore some of the nearby forests.

 

One of the unexpected joys of this was that we got to try something you can rarely do in Ireland- snow tracking. We were ostensibly searching for marten scats (droppings) and footprints in one of the forests around an outlying bunker in the Nietoperek tunnel system. But the forest seemed to be alive with all kinds of wildlife, their tracks and signs everywhere, even though it had only been snowing for a few hours and was still broad daylight. We came across tracks of martens and squirrels under the canopy of the woodlands, hare and fox footprints crossing one of the open fields, myriads of roe deer tracks and even wild boar hoof prints, which I was particularly excited about. Continuing through the forest, we even came across a boar “wallow” and scratching post, where they were coming for a mud bath and a good scratch of the back against an old pine tree.

Boar footprint in the mud, with coin for scale.

Boar footprint and possible marten scat in the mud, with coin for scale.

Not long after, we were crossing another large open field next to the forest when we saw what looked like a large, black dog plodding away from us over the ploughed earth. It quickly dawned on us (to my delight) that this was a wild boar, and we quickly followed it to get a better look. It disappeared into a dense thicket of bushes and long grass and we promptly followed it, because thrashing around blind in the bushes where you might come across an angry boar you’ve cornered is of course the most obvious thing to do when you spot one. Somehow we avoided getting gored but lost track of the boar, so we continued on through the forest. There are reports that wolves have recently made their way back to this very corner of Poland after having been hunted to extinction in past decades, but we weren’t lucky enough to see one that day, sadly.

 

Everywhere in this place you get reminders of the past, both hidden deep in the forest and in the heart of the village. This entire area of what is now western Poland for hundreds of miles around has swung repeatedly between the control of Germany and Poland for centuries, with waves of settlement from both directions. Although this area formed the heartland of the first Kingdom of Poland in the Middle Ages, German settlers were over time gradually drifting into many areas of Poland from across the River Oder to the west. This was followed by the chipping away of Poland’s territory by a series of land-grabs by German states, so that by the late 18th Century the area was known as South Prussia, part of the formidable Kingdom of Prussia. Although Poland rallied and took it back for a time, by the end of the 19th Century this was firmly part of Prussia, the leading state in the new German Empire.

 

You can see this when you arrive in Wysoka, which was then known as Hochwalde. The village looks German. The houses look German. The headstones in the churchyard are engraved in German. You can imagine German peasants leading their plough-horses along the neat cobble-stoned roads, many of which still exist unchanged, out into the fields to till the sandy soil to grow their crops.

Memorial to the former German citizens of Hochwalde (now Wysoka).

Memorial to the former German citizens of Hochwalde (now Wysoka).

In a roundabout way this all explains how the bats got here, because in 1939 instead of German peasants walking to their fields, German soldiers were marching along these roads eastwards to invade Poland and the Soviet Union during the Second World War. Well before the declaration of the war, in 1934, a network of enormous fortified lines began to be built across the eastern border of Germany on the orders of Hitler, as a last line of defence should an enemy appear from the east (i.e. the Russians). Hitler took a personal interest in the project, and the present structure (then known as the “Ostwall”, although another “Ostwall” was later built further east) was completed by 1938, but further planned works were postponed by the war.  In this area the engineers of the German Army sank shafts 40 – 50 m deep into the sandy soil, and from there began to burrow a series of connected tunnels, reinforced with concrete, stretching for over 32 km underground. These tunnels contained enough space to house an army, including barracks, magazines, warehouses, guardrooms, machine-gun posts and even an underground electric railway, complete with train stations.

 

Above ground, the tunnels were connected to a fearsome array of bunkers, machine-gun nests and gun turrets housing massive field artillery. These were further protected by mine fields, long ranks of “dragon’s teeth” which were concrete obstacles designed to stop tanks and armoured vehicles in their tracks, water channels connecting lakes and streams and areas which could be flooded if necessary, all of which were designed to lead enemy soldiers and tanks into “killing fields” where they could be shot or blown to pieces and held back on Germany’s border. The entire landscape was turned into an enormous fortress.

Concrete "Dragon's teeth"- anti-tank barrier.

Concrete “Dragon’s teeth”- anti-tank barrier.

However, it all proved to be in vain. When the Red Army approached the Ostwall in February 1945, the advance of its front line was so fast that it surprised the defenders before they realised what was happening. The Soviets rapidly smashed their way through it and continued marching on to Berlin, leaving the last hold-outs to be mopped up afterwards. Germany was totally defeated; not long after the end of the war the entire German population (those who had not fled for their lives or been killed in the fighting) were uprooted and deported west, their land becoming part of Poland once again and their homes given to Polish refugees from the east, where the Soviet Union had also moved its border westwards. The Ostwall had been completely useless and was abandoned, its tunnels and bunkers either blown up or left to moulder away in the depths of the forests or as eerie reminders of the war on the edges of the villages.

 

After a short period of use for storage by the Polish Army, the fortress was largely forgotten about and many of the tunnels were blocked to prevent people entering them. However, over time the tunnels began to be slowly colonised by bats, which love the very dark, damp conditions with constant temperature of about 10 degrees Celsius, as they are perfect for bats to hibernate in. Around the 1980s it was recognised that the tunnels had become a very important bat hibernation site and part of the site gained protection as a reserve as a result. More recently, the entire site and some nearby wetlands are now protected as a Natura 2000 site as there are somewhere in the region of 35,000 to 40,000 bats of several species which hibernate here, making it one of the biggest congregations of hibernating bats in Europe.

Abandoned bunker in the woods near the village of Boryszyn, part of the former Ostwall.

Abandoned bunker in the woods near the village of Boryszyn, part of the former Ostwall.

So how does this actually get figured out? Well, here we’ll pick up where I left you in the forest. The day after, more people begin to arrive throughout the day, until about 100 people have gathered by late in the evening in this small hotel with maybe 10 rooms, people are crammed about 9 or 10 to a room and even overflow into Yola’s house, and some have to stay in hostels scattered through the village. This is a big gathering of bat researchers (and just plain bat nutters) from across Europe: our small Irish group (although I’m the only person here for the bats), large groups from the UK, Belgium, the Netherlands, Germany and of course Poland, as well as smaller numbers from other countries including the Czech Republic and France, as far as I can remember.

 

We pile into the restaurant for dinner and afterwards we get the mandatory safety talk and explanation of the survey method, our survey teams and leaders, as well as an update on how last year’s count went (35,183 bats counted in 2012) and a brief talk about the ongoing pine marten work- cue sharp intake of breath when the crowd of bat people hears that the pine martens are eating their bats. The whole tunnel system of approximately 32 km, plus bunkers, will be divided into 9 sections, each of which will be surveyed by a team of about 8-10 bat people, plus 1 marten person. Towards the end of the talks, the drinking begins- well, actually it began well before dinner, but I have to pretend we were being responsible during the talks. However, around 11 or 12 pm people drift away to pack and get some sleep as we have an early start in the morning.

 

The alarm wakes me at about 3:30am, and as soon as I get up it’s action stations. Get up, get clothes on, check gear. Need boots, warm clothes, waterproof gear, head torch plus spare, hand torch plus spare, a rake of batteries. March downstairs into the dining room where there is pandemonium. Over a hundred people queuing up for their lunch for the day, breakfast, and most importantly, coffee! Wolf down breakfast and suck down a few cups of coffee then head out into the yard to meet my team. This includes our leader Henry, Kate and Kirsty from the UK, Ben from Belgium and Pete, who’s over with me from Waterford, who is our team pine marten surveyor. It is about 4:15 am, dark, snowing and bloody freezing. We need to be heading down into the tunnels by 5am, so we head away straight away, navigating our way through the traffic jam outside the hotel.

 

We drive out of the village, trying not to skid on the ice and hoping no drunk-drivers will come our way, before turning off for the forest near the neighbouring village of Boryszyn where we meet Tomasz (or Tomek), who will be our guide for the day, sucking down several ciggies before he goes underground as he won’t be able to smoke for the day to avoid disturbing the bats. When he is ready, we walk through the forest to the remains of an old bunker (“Panzerwerk”), the above ground part of which has been largely obliterated by high explosives. In the middle of the flat concrete surface is a shaft with a narrow metal staircase leading down to a locked steel gate, one of a small number of accessible entrances to the fortress. Tomek unlocks the gate, and we head underground.

Guard post inside abandoned bunker, Nietoperek.

Guard post inside abandoned bunker, Nietoperek.

The first thing we see is the guard post for the former bunker, several rooms complete with bunk beds and the commander’s desk. We are still only 4 or 5 m underground. We must pass through several reinforced steel gates, inserted to prevent the entry of the bunkermen (of which more later), and then descend a long flight of concrete stairs to the bowels of the tunnel system. We are now about 50 m below ground, and must walk about 1 km to get the section we are surveying.

 

Bahnhof Nord- old train station in Nietoperek tunnel system.

Bahnhof Nord- old train station in Nietoperek tunnel system.

The first landmark we pass is Bahnhof Nord, one of the train stations which the electric railway used to stop at. We need to keep our bearings, as much of the system just consists of endless tunnels vanishing away into the dark or shafts leading up to the bunkers and gun batteries which have collapsed, are too dangerous to climb or just blocked up. There are only four exits out of the whole system, so we don’t want to get lost- it has happened before.

 

As well as the risk of getting lost, we have to get accustomed to the other dangers and precautions. The golden rule is don’t walk backwards! People do this by stepping back to get a better look at a bat on the ceiling, forgetting that there are numerous uncovered manholes on the floor. There are also even deeper shafts leading to god-knows-where that you can’t see the bottom of, mostly filled up with dirty water. There are collapsed or half-collapsed tunnels and shafts, where the sandy earth has burst through the concrete walls and claimed back the tunnel, and where more collapses are possible. There are rusty and collapsing staircases 50 m high, metal floors over deep cavities which are held together by rust, uneven floors and piles of unstable rubble, partially-flooded tunnel sections where the holes in the floor could be treacherously hidden. People have died or been seriously injured down here, so there’s no room for losing concentration.

 

One of the dangers- a wide-open manhole in the Nietoperek tunnel system.

One of the dangers- a wide-open manhole in the Nietoperek tunnel system.

We arrive at our section and then we get our survey team organised. We will have two lead bat counters, one on either side of the tunnel, who will be followed by two sweepers who will follow behind to make sure that no bats have been missed or misidentified. We also have a recorder and map reader to count the bats we are identifying and calling out, and two floaters to check particularly awkward spots in more detail and to triple-check everything has been counted properly, trailed by the pine marten surveyor at the back. Although I am used to surveying for bats at home with a bat detector or ferreting out roosts by looking for their droppings, I have only seen a bat up close on a few occasions and in any case many of the species here are new to me. I have to admit to feeling overwhelmed at how much I have to take in and be aware of, but Henry helps me by pointing out the salient features of species after species as I follow as his sweeper and slowly I get the hang of things.

 

There are bats absolutely everywhere in these tunnels. They are hanging off the ceiling, on the walls, in holes and crevices in the walls, tucked behind metal brackets, wires and pipes, wedged inside pipes. There are tiers of narrow ducts or pipes drilled into the walls at intervals which once contained dynamite designed to explode and block up the tunnel in case of invasion, and we find bats wedged a foot or more inside them. They are inside the hollow metal handrails of staircases. We have to be careful not to kick or step on old beer cans as some bats like to sleep inside them, especially Natterer’s bats for some reason. Others sometimes crawl into the cracks in piles of rubble on the ground, so we also have to be careful there. They are hidden in almost every space imaginable.

 

Large cluster of greater mouse-eared bats hanging on a tunnel wall in the Nietoperek system. Try to count how many bats are in the group!

Large cluster of greater mouse-eared bats hanging on a tunnel wall in the Nietoperek system. Try to count how many bats are in the group!

We are in one of the least populated sections of the tunnel system, but even so they seem to be very densely spread. Some places have more bats, other places have very few; they seem to like the damper areas, probably because they get less dehydrated there while they’re hibernating. We have to be careful not to disturb them too much either, because if they wake up they burn up a lot of fat very quickly just by doing this- they risk not having enough fat left to last them through the winter and they could starve to death in their sleep. So we have to count them quickly and move on, a military operation marching unrelentingly through the tunnels.

 

Ben counting barbastelle bats hibernating in clusters on the tunnels walls, Nietoperek.

Ben counting barbastelle bats hibernating in clusters on the tunnels walls, Nietoperek.

There is a nice variety of bat species here. Some of them I am familiar with, or least know something about, even though I have rarely seen them up close. Daubenton’s bats (Myotis daubentonii) are very common here, probably the second most common in numbers. Brown long-eared bats (Plecotus auritus) and Natterer’s bats (Myotis nattereri) are also reasonably numerous. All of these I know of from Ireland. However, the tunnels are dominated by a rather exotic species for me, the greater mouse-eared bat (Myotis myotis), which is by far the most numerous bat species in these tunnels. They are much bigger than the other bats, one of the biggest bat species in Europe. I would put them at about the size of blackbird, which is large enough, compared to the wren size or smaller of the others I just mentioned.  These are present in big clusters of hundreds of bats together, and in some places we simply take a photograph for the individual bats to be counted later. Also present are barbastelle bats (Barbastella barbastellus), which are unfamiliar to me as they are absent from Ireland- they are crammed into small cavities on the walls at regular intervals, ten or so squeezed in tightly together, with flat faces like little black pugs, big ears and velvety black fur. These were fairly common in one particular area of our section. We came across a handful of whiskered/Brandt’s bats (Myotis mystacinus and M. brandtii), which are very difficult to tell apart, and a I remember seeing a single serotine bat (Eptesicus serotinus) tightly wedged inside an explosives pipe. There were other species I would have liked to seen that are present in other parts of the tunnels but not in very large numbers, including pond bats and Bechstein’s bats (M. dasycneme and M. bechsteinii). That adds up to ten bat species that I know are present in these tunnels, although there may be small number of additional species present which I can’t recall. The bulk of the total number of bats in the tunnels is dominated by greater mouse-eared and Daubenton’s bats.

Cluster of barbastelle bats in a tight cluster in a hole in the concrete tunnel wall.

Cluster of barbastelle bats in a tight cluster in a hole in the concrete tunnel wall.

As we continued through the tunnels we saw signs of the presence of other people. The entire length of the tunnels is plastered with graffiti. Just like graffiti everywhere, most of it is bad, some of it is good and some of it is downright creepy. People have obviously been coming down here for years, in spite of efforts to stop them from doing so. Apart from the blocked entrances at ground level, there are massive reinforced steel gates at intervals along the tunnels, designed to stop people from getting far into the system. They still keep coming in- sometimes explosives are used to blow up the gates. The people who come down here, the bunkermen, seem to be a strange breed. In some places you find signs that they have been around, sometimes even campsites. They apparently come down here and stay for quite some time, doing god knows what. There are usually a lot of beer cans strewn around the place so that explains a lot, but I’ve heard strange stories of groups of men being seen marching through the tunnels dressed in full German Army battle gear, frog-marching in the dark. Many of these people are probably harmless enough and just being nosy, but you get the impression that there could be some very strange and frightening people down here at times.

 

Close-up of smaller group of greater mouse-eared bats.

Close-up of smaller group of greater mouse-eared bats.

Halfway through our survey, we saw lights far ahead of us in the dark and we knew they could not be another survey team as there was supposed to be no-one else in the area but us. Tomek, our guide, went ahead to find out who they were and caught sight of two men disappearing ahead of him into a side-tunnel and when he turned the corner he saw no more sign of them, but they were evidently bunkermen who had broken into the tunnels somehow. Something about all of this creates a rather oppressive atmosphere which is unnoticeable at first but gradually builds while you are down in the tunnels. I have been down here before in small groups of two or three people and there is a palpable sense of something eerie or menacing about the place, and the hairs are nearly standing up on the back of my neck now thinking about it again. It is worse in some places than others- some of the bunkers in particular, especially you see that a group of bunkermen could have been here five minutes ago, or when you find some of the weird little candle shrines people have set up in odd corners. In one place we encountered a cross and flowers on the spot where a girl fell to her death down an uncovered shaft when she came exploring from above ground in the dark without a torch. It’s not so bad with this large group though, when you are marching through the tunnels and counting the bats is keeping you occupied.

 

At one point we climb up one of the shafts towards a blocked up bunker to see a summer bat roost site. The air becomes noticeably colder again as we climb up the concrete stairs. Along the way we find many marten scats and some footprints, so they are evidently coming in this way. Towards the top, the concrete stairs are completely encased in ice, so we have to be extremely careful- although there is a low wall around the edge of the staircase, the landing at the top of the shaft is completely open so a simple slip could end in disaster. We come to another reinforced steel gate at the top of the stairs and peer through. On the other side is a derelict bunker lit by sunlight filtering through another gate leading outside; the small amount of light and a breath of wind is welcome, as we have been underground for about six hours by this stage, although it is easy to lose track of time while underground. In the far corner of the bunker away from the gate is the site of a summer maternity colony of greater mouse-eared bats, where several hundred of the greater mouse-eared bats now sleeping below come in summer to give birth and raise their young. There is a sort of chimney rising out of the bunker which heats up nicely in the summer sunshine, which is what the bats love about it. Below the roost site is a massive pile of bat guano, about five feet high. Although some of the bats stay here in summer, most of them migrate here for the winter from hundreds of kilometres around, some of them having been found to come from beyond Berlin and some possibly even farther.

 

Interior of an abandoned above-ground bunker in the Nietoperek tunnel system. This is the same bunker as in the photo above. The site of the greater mouse-eared bat summer colony is just to the right of this photo.

Interior of an abandoned above-ground bunker in the Nietoperek tunnel system. This is the same bunker as in the photo above. The site of the greater mouse-eared bat summer colony is just to the right of this photo.

Back below ground we continue with the survey, which rarely stops: you just get into a flow of searching, finding, identifying, counting, calling out, moving on. Although we take a few short breaks mostly we just keep ploughing on, as although we have one of the least populated sections we still need to keep moving if we want to be finished by the end of the day. We have only one day to do this as repeated entry into the tunnels would cause too much disturbance to the bats. Eventually though, after about 8 or 9 hours we finally finish up our count. After a long march back through our section we make it to the exit shaft, climb the concrete stairs and pass through the three gates guarding the entrance.

 

It is an interesting feeling emerging back into the sunlight after a prolonged period underground, like emerging back into the land of the living. All your senses seem to be heightened as you have in effect experienced a full day of sensory deprivation underground. Obviously there is no light other than your own torches, and if you switch them off for a few minutes the darkness is total. There are very few smells underground apart from the odd whiff of stagnant water or very rarely the reek of a dead animal- mostly the very dry dust and sand clog your nostrils, and make your skin and tongue feel dry. And apart from the noise you make yourself, the clump of your boots on the concrete, your voices, the echoes you make, and your own breath, or the occasional chittering of a bat or plink of water, there is no sound at all. There is no breeze underground, except a slight one near the shafts to the surface. But when you re-emerge, all of this sensory information floods back to you in an instant. The light is blinding and colours seem brighter, all of the background noise that you usually take for granted such as birdsong or the wind in the trees seems odd. Strongest of all are the smells- the crisp winter air with a bit of pine-scent here. Another one that I can’t explain fully is a sort of strong earthy smell, a bit like damp woodland soil or the smell after rain- it’s like the smell of life returning after you have been stuck in the dry, dusty tomb underground all day.

 

For a time after we emerge we stand around in the forest enjoying the snow, and then we make our way back to the hotel. We arrive around 2pm, and we seem to be the first team back. We relax with a few beers, and I count up the number of bats in our section- about 1,200 as I remember, so it’s an increase on last year’s count. As I have to leave early, I pack and take a last look around Wysoka before I have to get a lift to catch a train back to Berlin from Swiebodzin later in the evening. As I am leaving the hotel, more of the bat people are arriving and the dining room is becoming crammed again as people gather in anticipation of that evening’s celebratory meal and final talks to find out the final tally of this year’s survey (I later find out it was around 37,000, an increase on last year). Unfortunately I have to miss out on the celebrations, but I am told that, true to tradition, the amount of drinking was epic later that night…

 

And so that ends the weekend I had taking part in the bat survey of Nieteoperek. Taking part in the bat survey was an intense experience and the underground tunnel system is in many ways a very strange and interesting place, but overall I count myself very lucky to have experienced all of this.

Wysoka Lake, January 2013

Wysoka Lake, January 2013

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