Climbing trees by Eurasian lynxes to emit territorial and mating calls in Belarus: pressing questions, knowledge up-to-date and difficulties to investigate this phenomenon

During the winter of 2017-2018 in Naliboki Forest we (Naust Eco Station and Wild Naliboki) have found that Eurasian lynxes climbed rather high pine trees to emit mating calls during the species mating season (Sidorovich et al., 2018). In total, during February and March 2018, we registered four such trees of the Scotch pine, on which adult male lynxes climbed for about 17-26  meters high. The density of the  local lynx population was about 4-5 inds per 100 km2 i.e. about 80 per  almost 2000 km2.  We have evaluated that phenomenon of calling by lynxes from a tall tree top as a mating call, also taking into account that it was registered in the lynx mating season in Belarus (mid-February-early April).

Below you will see the photo-material we have got in February-March of 2018.

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However as to these findings of February-March of 2018, there is the strange fact that earlier during the long period of 1998-2012 by doing more than 2000 km of snowtracking of lynxes, when  the species population density was lower than 3 inds per 100 km2 (usually between 1 and 2 inds per 100 km2),  we have never faced with climbing so tall trees by lynxes. The situation was really strange, and that suggested us about phenomenon of a territorial calling by  lynxes, when the species population density is rather high.

Then in Naliboki Forest in July 2018 we faced with fresh climbing a tall pine presumably by adult female lynx (that was mother with two kittens), because the tree was in the core area, where this mother lynx with two kittens were staying most of the time. That was badger sett area and kittens used a lot badger burrows (mostly outliers) to hide from mosquitos.

Then in Naliboki Forest again in November we registered at least two, maybe even three recent climbing of tall pine trees by lynxes in different lynx territories, and when in the late December 2018 there was discovered that a male lynx climbed tall aspen tree, we have started thinking about territorial calling by lynxes in the conditions of high population density. Having so many lynxes in Naliboki Forest, it appeared already too hard to do a precise census of lynxes. Camera trap registrations (60-80 camera traps were applied), track survey (twice per a month), snowtracking (about 260 km) suggested that during the winter 2018-2019 in the whole Naliboki Forest there were more than 80 lynxes, perhaps, about on average 6 inds per 100 km2. The local range of the species density was between 2 inds per 100 km2 in sand dune massifs and 14 inds per 100 km2 around the Biarezina medium-sized river valley with broadleaf deciduous forest.

These lynx climbing marks were made by lynx in February of 2018, and now in March of 2019 they are not light red, but alredy dark brown.
These climbing marks were made by lynx in February of 2018, and now in March of 2019 they are not light red, but already dark brown.

In January-March 2019 in Naliboki Forest we (Naust ecostation, Wild Naliboki and Maximilian Hetzer)  registered 42 new trees, which were climbed by lynxes (see the tree distribution maps). In total in this period we registered 60 recent climbing of trees by lynxes, 41 of them were  climbed during late February and March (mating season in lynxes), which is evidently more often (68%).  The facts of climbing tree by lynxes were mainly registered by fresh (still light red in the case of pine trees) claw marks on the bark, recent broken dead branches on a height, a lot of small bark remains on snow surface around the tree as well as in three cases by stepping on camera traps on the height of 2-5 meters and  fragments of lynx fur taken by the cameras in these cases.

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Lynx climbed this aspen tree for a territorial call in the end of December of 2018. Photos by Siege Van Ballaert and Reinhardt Strubbe.

 

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The trees which were climbed by lynxes in  Naliboki Forest in 2019; lynx claw marks on the tree bark and pieces of lynx bodies that were photographed by cameras fixed on the tree trunk.

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In the case of trunk without branches there should be thick and outstanding  bark segments about on average 5 cm wide by 15 cm long, which can be grabbed by climbing lynxes. Such a tree should have a rather broad stem.  In the case of climbing by grabbing thick bark segments of broad trees, lynx leaves really few small claw marks.
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Lynxes usually do not climb on broad stem tree with relevant  branches, suitably located, but without thick outstanding bark segments like this one.
F59A3538WEbIf there are solid branches on the upper half of trunk, a lynx, while climbing, uses them to jump from branch to branch.

Lynxes may climb trees without branches having a relatively narrow trunk of 30-40 cm  in diameter and no thick bark segments. In this case lynx  encircles the trunk with its fore paws, while the claws of hind paws are stuck in the bark. In the case of such a climbing usually there are markedly more lynx claw marks on the tree.
P1020744WebTo register lynx climbing of a tree, we put camera traps on the neighboring tree on a distance of 4-6 meters. The camera trap is placed in vertical position and it has  in the frame 4-6 meters of the trunk of the tree, on which we guess a lynx will climb.

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Not a high pine trees, which were climbing by lynxes, while jumping from one branch to another one (alive one or only dry broken one, but solid enough); the same it jumped down using the branches.

Lynxes like to climb a tall tree by walking there along another tree that was inclined on that targeted  tree.

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Oaks that were climbed by lynxes for territorial calls. See the only marks on moss and something negligible  on solid bark.

Still we have not got a good photo or video of Eurasian lynxes climbing a tree, because as we learnt for the moment that (in the majority of cases), a lynx runs towards the stem (or tree trunk) and jumps on the tree that it decided to climb. In this case a lynx can jump 3-4 meters high on the stem. Climbing down trees, a lynx mainly jumps down from the height of 4-6 meters. So, on camera traps you see photos of the trunk, but already  without the lynx, because in the majority of cases camera-traps are not fast enough to capture a climbing lynx. In February-March we got three such failures. However, we still hope to take photos of a lynx that is  climbing a tree, because claw marks on the tree bark suggest that sometimes before climbing, a lynx smells the tree stem and begins climbing without jumping. When a lynx is climbing down, it may sometimes also reach the ground level without jumping down.  To register lynx climbing of a tree, we put camera traps on the neighboring tree on a distance of 4-6 meters. The camera trap is placed in vertical position and it has  in the frame 4-6 meters of the trunk of the tree, on which we guess a lynx will climb. Other possible ways of taking such a photo are rather time and labour-consuming and need more quite large equipment (e.g. ladder), and in our system of working they are still not possible. Perhaps, we will undertake other approaches to take photos of lynx climbing trees, if we finally failed with the method we use for the moment.

It’s worthwhile to return to the question of why we did not find out this behaviour before, having so much lynx snowtracking experience. We assume that lynxes did such climbing and calling from a tall tree before too, but not so often. The key point is: what is much lynx snowtracking? In 2018-2019 in Naliboki Forest, when lynx climbing trees was registered more or less often by us, we did about 260 km of snowtracking and during just this kind of study we have registered merely one climbing of a tree top. So before, by doing 2000 km of snowtracking, we could potentially reveal about 8 such climbings of trees by lynxes. But in the conditions of the lower population density of  lynxes, in which the study were carried out,  undoubtedly lynxes emitted  territorial calls and did other marking of the territory markedly less frequently (as all other vertebrate animals). Additionally, the main aim of the lynx snowtracking we did before was to reveal the home range of lynxes by multi-tracking of the same individual. We were in a hurry to do as many as possible km of snowtracking and did not pay much attention on details. Also, a marked part of that snowtracking was done by my assistants, who might have been less focused on lynx behaviour. So, from the above we see that that 2000 km of snowtracking, when the lynx density was lower, is not a good enough argument that lynx did not climb trees during that time. Possibly they did, but less frequently than nowadays.

So, currently we state that lynxes emit territorial calls almost year-round,  particularly when the species population density is high (4 and more inds per 100 km2). Perhaps, in non-mountainous forested areas  lynxes emit territorial calls from an elevated position, mainly by climbing a tall tree. Just before and during mating season, such a call of adult males plays a double role, and indicates both occupation of the territory for other possible adult males in the surrounding area, and attracts females in heat.

Now it should be addressed, on which trees lynxes prefer to climb. First, I will state that such an information, while you search for such a tree by inspecting a number of trees, will be more or less biased, because mainly pine trees are relatively easy  to find during such an inspection due to visible lynx claw marks on the soft bark. However, while snowtracking and just checking trees with a snow cover, we also found lynx climbing on aspen, spruce and oak, and in these cases there were almost no claw marks on the stems with the exception of three oak trees. So, only pines that were climbed by lynxes were more or less easily found and they prevail among the 51 lynx trees that were registered by us in Naliboki Forest in 2018-2019: 2 aspen, 6 oaks, one spruce and 42 pines. 22 (43%) out of 51 lynx trees were situated on small hills (in Naliboki Forest there are no high hills, it is a flat terrain); 12 of lynx trees (24%) were situated on recent clearcuts without any tree stand around.  Only 6 (15%) out of 39 lynx trees that were situated in a tree stand were slightly lower than the forest canopy level, whereas others (8 or 21%) were on the level of the forest canopy  or even higher than the forest canopy (15 or 64%). At the top of lynx trees there should be at least one suitable branch to sit and emit calls. In two cases such a suitable place was formed by raven and buzzard nests.

Lynxes chose trees either almost without branches on the  stem below the sitting branch, or trees having a row of stable and solid branches. In the case of trunk without branches there should be thick and outstanding  bark segments about on average 5 cm wide by 15 cm long, which can be grabbed by climbing lynxes. Such a tree should have a rather broad stem.  In the case of climbing by grabbing thick bark segments of broad trees, lynx leaves really few small claw marks. Alternatively, lynx may climb trees without branches having a relatively narrow trunk of 30-40 cm  in diameter and no thick bark segments. In this case lynx  encircles the trunk with its fore paws, while the claws of hind paws are stuck in the bark. In the case of such a climbing usually there are markedly more lynx claw marks on the tree. If there are solid branches on the upper half of trunk, a lynx, while climbing, uses them to jump from branch to branch. Also, lynx like to climb inclined trees. In this case it can just walk up along the inclined stem.

Interestingly to emphasize that at the Biarezina valley with  old deciduous broadleaved forest, there is the highest local number of lynxes (20 inds in the winter 2018-2019) on not a large area of about 140 km2. In this area, we found 26 lynx trees (a half of the lynx trees discovered or about 19 lynx trees per 100 km2 ), while in the rest of the about 660 km2 of model area in Naliboki Forest we found only 25 lynx trees (about 4 lynx trees per 100 km2).

Also, it should be described  some information available on lynx calling itself. First, while working with carnivores  and other vertebrate  predators  during almost 35 years in the wild and sleeping in the wild perhaps about two years (approximately about 700 nights) in different seasons, I definitely heard lynx calling only for three times. That was mostly when the lynx population density was not high (mainly about 0.5-1, sometimes about 2 inds per 100 km2), and I had no idea that they may call from a tree top. Two lynx callings were heard at night and one was registered during dense twilights also when it was almost dark.  I would say that the callings were rather long-lasting. In one case lynx was calling for about three hours; sometime there were 5-15 calls per a minute and sometimes there was a brake in calling for 3-10 minutes. In nights, when sound travels relatively faraway, the lynx calls I could hear at a distance of about 2 km maximally. Nowadays, trying to remember and analyse my memories of those lynx calls, I realize that, at least, two of the lynx callings were emitted from a tree top, because the lynx positioning was not changed for about one hour in one case and about three hours in another case.

Interestingly to notice that in Belarus among the nature-related people (like hunters etc) everybody knows that wolves howl, but with the exception of one life-long hunting warden, nobody knows about calling by lynxes.

Generally, for the moment there are more pressing questions than complete knowledge in relation to climbing of trees by Eurasian lynxes to emit territorial and mating calls. Possible questions are as follows. How often do lynxes call in non-mating and mating seasons? As to non-mating i.e. territorial calls, how are they seasonally or monthly distributed? Is lynx calling weather-related? How long is lynx calling going on? Other characteristics of the Eurasian lynx calling are poorly known as well. Do only adult male lynxes emit territorial and mating calls or do adult females call too? How often do lynxes use the main and secondary calling trees? What is the real tree species proportion between the lynx trees? How much is calling by lynxes density-related?  What is the proportion of calling by lynxes from trees and ground surface  in forested areas with a more or less flat relief? No doubt, there is a lot unknown in relation to the climbing techniques by Eurasian lynxes; it should differ from that of Canadian lynxes, which are markedly lighter.

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