The third and last of the bat detector workshops in 2001, organised within the frame work of the Eurobats transboundary program "bat expert training and data collection in south east Europe" took place between September 18th and 24th in Yugoslavia. Six participants from Serbia and Montenegro participated. It was made possible through financial support by the German Federal Agency of nature Conservation and the NGO ‘Milieu Kontakt Oosteuropa’. Milan Paunovi? had organised the whole event to be concentrated on the magnificent surroundings of the Obedska bara. These Obedska marshes are in fact a giant old oxbow of the river Sava near the villages Kupinovo and Obrez, about 60 kilometres west/south-west of Belgrade. An area where Milan’s colleague Branko Karapandza already had collected a lot of data using mist nets. We were housed in Obrez in a motel overlooking the scenery of the marches, which was run by the state forestry department, and where the personnel was very friendly and very patient regarding our unusual activity pattern. Ideal, because all we had to do was to step outside to be in our research area. And I will not even start to talk about the general beauty and species richness of the area, and all the birds, butterflies, amphibians and reptiles et cetera which were just everywhere.

Milan and myself went to Obrez in the afternoon of the 18th of September to check out the place and have a first look at the bats, the timing of dusk and emergence et cetera, to be prepared. Unfortunately it poured with rain all day and night. We couldn’t do much. Luckily it was the last rainy day of an unusual wet and cold ten day period.

On the next day all participants arrived and theory sessions commenced. For the evening, we decided to just start watching bats and practice working the detector just outside the motel. At about 18.30 hours, at the beginning or dusk, we waited for the bats, overlooking the marshes and with a beautiful view on the old floodplain forest on the ‘island’ between the oxbow and the current Sava. The first to be expected and the first to appear were Noctule bats. Suddenly they were there, high up in the air above the marches in straight fast flight and with long QCF sounds going down to as low as 17 kHz. For a moment I stood wondering whether they could be Greater Noctules (N. lasiopterus). But, although big, they were too small and in listening and watching for a longer time, the lower longer QCF pulse was on 21 to 19 kHz like it should be. The lower readings were a result of bats flying high and straight away from us, where the bat goes down to its lower limit in the QCF frequency, and the downward Doppler shift adds just another bit. We were at quite a distant to the forest in front of us, but still they seemed to be coming from there. Running against the stream was impossible, we had to organise some boats for the next evening. Some passing Serotines (Eptesicus serotinus) confused those listening to the Noctules and in fact working with detectors for the first time. But that was exactly what we needed: similar species, to practice tuning the detector and figuring out which of them it is.

A few Pipistrelle bats (Pipistrellus pipistrellus) added a new dimension. Focusing on the ‘lower’ species, on the 25 to 20kHz bandwidth, will have you miss those on higher frequencies, you have to scan all relevant frequencies. And this immediately made us tune even higher. Because small bats were flying there around and under the trees and we didn’t pick them up at the 45 kHz where we received the Pipistrelles. Bingo: expected and hoped for to be there, but not recorded yet in Yugoslavia: Pygmy pipistrelles (Pipistrellus pygmaeus). Excitement amongst the bat workers about a new species added to Yugoslavia’s extremely high biodiversity. Of course time expansion recordings were made for analysis and every body practised to differentiate between pipistrellus and pygmaeus using a heterodyning detector. Already thinking about the possible occurrence of pygmaeus in their ‘home territory’.

We headed for a forest with large old trees on our side of the marshes. Since it had been raining heavily for the last ten days this was quite a slippery and muddy experience. Besides the different species of owls we heard, the forest appeared to be rather silent on the part of the bats. But then we entered a territory of a calling Pygmy pipistrelle male. Here we just stood for a while listening, studying, recording, discussing frequencies, wondering why in calling males the normal echolocation sounds are not heard at all, or only very weak, and just enjoying the power and dedication that such a small bat puts into his display song. Every now and then a Noctule was heard above the forest.

Our route sampled just a little bit of the forest of course, but there didn’t seem to more of them calling anywhere. On our way out we encountered just one silent gleaning bat, which very probably was a Natterer’s bat (Myotis nattereri), but was heard and seen to short to be sure.

In the meanwhile the night got unusually cold and foggy for a Yugoslavian September night and we wondered whether this accounted for the low activity in the forest. But we wouldn’t give up and headed for Obrez and some old fish ponds where open water and something like Daubenton’s bats might be expected. Again a very wet and slippery exercise, but we made it to the fish ponds, only to find them almost completely overgrown. No Daubenton’s on the little bit of open water, but again and again a Noctule passing somewhere high above us. On our way back to the village we encountered a Nathusius pipistrelle (P. nathusii). Another species, but unfortunately an observation too short to really explain anything at this moment. In the village, activity was a little bit higher. Here and on our way back to the motel we again and again encountered Pygmy pipistrelles. They were occasionally using social calls, but no clear display behaviour was shown at this stage of the night.

After a break some of us went to the Sava by car. At about ten kilometres from Obrez at the little ferry between the village of Kupinovo and Skela the only possibility to easily get to the Sava was located. There is hardly any roads or tracks close to the river, and since the floodplain forest alongside the river was flooded at the time, the Sava was virtually inaccessible, especially during the night. Standing on the ferry helped us having a good view over the water. And almost immediately after setting up our gear, we observed what we had hoped for: Pond bats (Myotis dasycneme). Not very often, but regularly some of these ’oversized Daubenton’s bats’ passed at high speed with clear tonal quality at about 33 to 38 kHz. Of course, along with the recordings of the Pygmy bats, these were the first to be analysed and demonstrated the next morning. And here on the open water, patrolling along the vegetation on the river bank we again found Nathusius pipistrelles. This time they gave us all the possibility to work on imprinting their rhythm and frequencies. A very good first night!

On the second workshop night, September 20th, Branko Karapandza and Ceda Ivanovic stayed at the motel premises and put up a net on a place where Branko had have good success in catching bats before. We all were very interested to try and catch some Pygmy pipistrelles.

The rest of us Milan, Srdjan Stamenkovic, Marija Stojic, Andrej Conti and myself, set of to be the amusement of the local people. We had borrowed some of the narrow wooden boats, which the local fishermen use to ship through the narrow channels through the reed. We, at first, had a lot of problems staying out of the reed. But finally we managed.

Our goal was the old floodplain forest on the island between the oxbow and the Sava. A wonderful trip through the reed and willow vegetation, and numerous wonderful water and wetland plants, which are conquering ground in the old riverbed. A paradise for wetland birds e.g. So no wonder these marshes have the international status of an IBA (important bird area).

Since the time the Sava has moved its main channel, the oxbow is slowly being filled with clay sediments. Every time the river floods the area its water brings new sediment. At this time the water in the river was relatively high and the marshes were filled with water, but even now only the middle strip in the oxbow still was open water. The island ahead of us in fact was a series of channels and elevations through which the Sava in older times has been flowing during high water, and which in extreme high water situations might still be flooded now. Huge old oaks and ash trees on the higher and dryer parts and willows and elder in the lower wetter parts. The complex is grazed with a mixture of domestic and wild pigs, but very extensively, leaving a well developed undergrowth. Now in the beginning autumn there was a wealth of mushrooms.

Already when we had just passed the open water corridor in the middle of the oxbow, and still were in the reed zone on the island side, the first Noctules and Pygmy pipistrelles appeared over our heads. Just before landing a small Myotid bat, probably Daubenton’s, flew low over our boats towards the open water. But we didn’t have time for them right now, because from the edge of the island I could hear the loud social sounds from a ‘Noctule tree’ at the time of emergence, and I wanted to be there before all bats had left. Before my boat had properly landed, I already jumped over via a few other boats to get to the land and headed for the sound. Luckily it took just a few minutes to make out the tree: an old dead oak. At a height of maybe 10 meters it had three different holes. Here several Noctules were swarming and circling and screaming around the tree and others kept coming out. A hectic situation, with a lot of noise, and several Pygmy pipistrelles flying through the scene. A rough estimate on the Noctules would be about 25 to 40 animals.

We started walking the island, several hundreds of hectares in size, keeping close to the edge to not loose our way and to eventually get back to the boats. This also would allow us to possibly see silhouettes of bats hunting just on the outside of the forest edge. But while the night grew darker it was remarkably silent. Until, at about one hour after sunset, the males of the Pygmy bat seemed to start their display flights. After finding the first one, they suddenly were everywhere. In about two hours, we, of course, only sampled a very small route on the whole of the complex, which was concentrated on the edge of the island. But on this route there was a calling Pygmy bat on about every 50 meters. If this is a representative sample, there must be a couple of hundred of them calling there. We recorded and observed them. Like in the Common pipistrelle bat, they were always flying around calling in their territory, which would have a diameter of about 50 to75 meters. We regularly got them chasing each other with an intensified rate of calling. Only very occasionally we heard a hunting or calling Common pipistrelle. When we were heading back to the boats, just one Myotid bat passed. Probably a Daubenton’s bat, but too short an observation to be sure.

We took the boats out on the open water between the reed to wait for Daubenton’s and maybe even pond bats. Floating amidst this wonderful moonlit scenery, with the reed and the forest on the background, different owls calling at a distant, and just a little fog starting to rise, we even forgot about the unstable boats, and just were ready for them. At a closer look, however, there was a lot of floating vegetation on the ‘open’ water and none of those trawling species appeared. But here, outside the forest, hunting activity was high. Numerous Noctules were hunting high above us, occasionally coming down. Quit a few Pygmy pipistrelles were observed hunting and calling above the open water and the reed. Would this be territories too? And every now and then a Common pipistrelle and a Nathusius’ pipistrelle passed by to give us possibilities to practice their rhythm and frequencies in the open environment, and to demonstrate their different social calls as compared to the Pygmy bats. At last we had to go back to the mainland.

The team at the net had not been lucky. They had had a lot of passing Pygmy bats, and Noctules, Serotines and even a Nathusius male calling from a tree, but nothing in the net.

After a break we decided to go to the Sava again. On our way there we stopped at several points where the road was just between the forest and the swamps. Many territorial Pygmy bat males again, and hunting Pygmy’s and Common pipistrelles. On our way trough Kupinovo we stopped at some streetlights. We hoped for Serotines, but got treated on a Pygmy and a Common pipistrelle hunting under one streetlight together. A beautiful chance to study the difference in size and flight style, and in where exactly in tuning up and down the one species occurred and the other disappeared. Occasionally a Kuhl’s pipistrelle would add to the puzzle. Our next stop was at the bridge of the channel connecting the marches to the Sava, just behind Kupinovo. Here we immediately found Daubenton’s hunting over the water, calling males of Pygmy bats – they were everywhere – and two trees with calling Nathusius’ bats. For those working with bat detectors for the first time, a good occasion to experience the fast and dry rhythm of many Myotid bats, the Daubenton’s in this case, and to study the specifics of this species. The night grew colder and on the Sava a dense fog was developing. Hunting activity wasn’t very high, but still Noctules were almost constantly above us, and an occasional Nathusius came by following the bank of the river. Again a few pond bats could be recorded. Bigger than the Daubenton’s we just had, flying faster and more straight and with tonal quality on 35 to 38 kHz. A good ending for this nights work.

On the third night of the workshop, Milan and Ceda were going to attend the nets, in a second attempt to catch the Pygmy bats. The rest of us went by car, back to the Sava near Kupinovo. We wanted to be earlier now, to see whether the activity of the pond bat would be higher. On the muddy road from the village to the river, and well before sundown, about ten or more Serotines were hunting along the road and forest edge. They were flying very low, at about 3 to 4 meters. So we stopped to watch them hunt, and listen to them for a while. An excellent opportunity, because it was still very light. The Serotines would be on the road and along the banks of the Sava all the rest of the evening, to be seen and heard hunting in different situations. Coming to the Sava, still under very light conditions, I headed for the place where the channel to the marshes connected to the Sava. If Kupinovo would be the place with a pond bat roost, this channel would be a good place to look for the flight path. At the time when I got to the connection, Daubenton’s bats were already flying out towards the river. In just a couple of minutes I counted another 60 to pass. So it was a flight path, but a Daubenton’s flight path. They all turned to one side keeping close to the bank. Sometimes it looked as if a larger bat was among them, but it was really very difficult to be sure. After this phase with the flight path was over, Daubenton’s would also be hunting in, and flying in and out of the opening of the channel to the river, and repeatedly passed by close to the bank.

Only after it was quite dark already, the first pond bat was spotted, further away from the bank. They must be coming from some more distant place. Our attention shifted to the Serotines, Noctules, Pygmy and Nathusius’ bats that were passing all the time. Just when we were focussing on a Nathusius’ bat on about 35 to 37 kHz, a ‘funny Nathusius’ came by, as Branko Karapandza commented. I was delighted, because this funny Nathusius, was a Barbastelle (Barbastella barbastellus) using only its 35 kHz qcf-FM pulse. It lacked the unmistakable castagnette rhythm, but was still clearly a Barbastelle bat. It passed us a couple of times so recordings could be made.

We went back to our home base, stopping at the channel and the street lights in Kupinovo again. Especially in the village, near the street lights, this revealed a very good learning situation. Four pipistrelle species were flying above the well lit streets. The Common pipistrelle and the Pygmy bat mostly circling the lamps and their direct vicinity, sometimes hopping to the next lamp, and Kuhl’s and Nathusius’ pipistrelles flying long stretches along the street lamps in a row. The first two were comparatively easy to identify, on their size, flight behaviour and frequencies. The second were definitely more difficult. But Kuhl’s pipistrelle keeping to a slow but steady rhythm with QCF on 41 tot 39, could be recognised as different to the Nathusius’ pipistrelle, with a much more variable rhythm and QCF down to 34 kHz. Regularly the social sounds helped in putting the name and rhythm together.

The team at the net had again not been successful. So, for now, our positive identification of this new species to Yugoslavia, based on the time expanded recordings of the Pygmy bat’s ultrasound, its social sounds, and the visual observation of the flying bats, cannot yet be backed up by identification of animals in the hand. But, since everybody is very motivated to get them, this will only be a matter of time.

After the break we tried a high observation hut, on about tree crown level, from which in daylight we would overlook the beautiful marshes. From this spot the constant activity of Noctules over the forest and the marshes was even more obvious then from the forest floor. In a kind or orchard, between the observation hut and the hotel, again mating calls of Pygmy bats were ‘all over the place’. A ‘gleaning bat’, however, a Geoffroy’s bat, which was only heard a couple of times, and which sounds were difficult to distinguish between the noisy Pygmy’s, was to be our last treat on the official workshop program.

On the next morning we had a final discussion in the official workshop program, with last questions and remarks, and after that everybody started travelling back home. Probably a little confused, with all these new impressions and information, and hopefully motivated to start working on this puzzle in their home regions, and to build experience from that.

I was to go back to Belgrade to look around in Belgrade and its surroundings on the next two nights. Most urging questions: will we find pond bats on the Sava and Danube? And, will there also be Pygmy pipistrelles in the Belgrade area? The first night in Belgrade. Branko and Marija took me to the south east banks of the Sava and Danube directly in the city. Quite early Kuhl’s pipistrelles were already flying in the build up area of this big city. On the banks of the Sava we found more of them, along with Noctules and an occasional Nathusius’ pipistrelle. No sign of any pond bat on the Sava and Danube, nor of any other Myotis, for that matter. In the parks of Belgrade, of which we only visited a couple, activity was highest. Here we observed territorial Noctules, Kuhl’s bats, again an occasional Nathusius’ and at least some Myotid bats, which were only heard and not seen and therefore unfortunately could not really be identified. The recordings showed that they have to be something like Daubenton’s or Whiskered/Brand’s bats. Remarkable – to me – was the relatively high activity of Kuhl’s bats even in the most central parts in the city. They were not only in the parks, but also in the middle of the shopping centre and above streets with quite heavy traffic. Pygmaeus was not picked up anywhere.

On the second evening Milan, Branko and myself went a little to east of Belgrade where the river Tamiš flows into the Danube. Very early in the evening, we already observed a large number of Noctules flying high, coming from approximately the direction of Belgrade and heading towards the Danube plain. They seemed to be ‘struggling’ against the wind, on something between 50 and 100 meter high. Sometimes they seemed to stay a one point in the wind without moving much. Sudden dives, forward or the side, with fast accelerations of their flight speed, gave the impression that they were just ‘hanging’ there to wait for insects to be blown in their direction. Their acceleration showed that it was not really a problem to be flying in this strong wind. When it got darker different Pipistrelle species appeared at the banks of the Danube. Again mostly Kuhl’s bats, some Nathusius’ and Common pipistrelle, but no Pygmy bats. Then when it got even darker, and after our patience was tested quite a bit, Myotid bats appeared over the water surface. Clear tonal quality on 35 kHz. No doubt, pond bats. Great! Like on the Sava near Kupinovo they were seen and heard regularly but in low numbers. We changed to a spot at the Danube inside the Belgrade build up area again, but now on the north west of the Sava and Danube. Here the river was flanked by trees and a large island with old floodplain forest was in front of us. Noctules were hunting in large numbers higher up on the river bank, and near the buildings and street lamps. We tried for the water at several spots. Directly on the edge of the water, it was Pipistrelle species again, and, in one site, Daubenton’s bats. No pond bats or Pygmy bats here. But...... who would complain about that, when a successful week of ‘batting in Yugoslavia’ ends with a beer on a boat just of the shore on the Danube. All you got to do is hold out your detector.......

Herman Limpens