Enigmatic warm-season behavior and ecology in Eurasian lynxes: pressing questions, hypotheses and results up-to-date

The behavior and ecology of the Eurasian lynx during the snowless season, particularly from the second half of April till the end of October (hereafter the warm season), is still searchless, and several important questions of study on the species in this seasonal period are seemingly even unknown. The main hassle is that the prevailing research method of GSM GPS telemetry  fails to investigate those questions. Basically this method only records coordinates and how active or passive the individual is. It looks like currently the single possible way to learn about the behavior and ecology during the warm season  goes through much routine habitat inspection, art skills to read activity signs of lynxes in snowless period and smart extensive camera-trapping.

This study approach is not cheaper than telemetry (intensive usage of off-roaders and many camera traps, which disappear and collapse all the time etc.) and it does not bring much reportable information. Therefore, it is almost impossible to apply this research approach within the project system that is mainly used in the academic zone, where a researcher’s life consists almost only of reporting, preparing scientific articles and applying for a next project. Respectively, many modern carnivore researchers have to be in their offices too much, instead of close to the species they investigate. In turn, such cabinet-based researcher can not read activity signs of lynxes, and smart camera-trapping of the species is not available in this case, too. Perhaps, all those are the main reasons why warm-season ecology and behavior of Eurasian lynx is still almost unknown.

What are the main pressing questions on the topic? First of all, there is the question regarding the denning in Eurasian lynxes in non-rocky regions (this is actually where most of the individuals of the species live in Eurasia). We (me, Irina Rotenko from the Naust Eco Station and Wild Naliboki team) have already addressed the question in the separate blog post and in our pilot book on the lynx behavior and ecology (Sidorovich et al., 2018). So, here I will not consider this question.

The second strikingly essential question is, do adult male lynxes take part somehow in raising of kittens, and if they do, how does the particular adult male lynx choose the mother lynx, for which he will serve? It is really curious, taking into account the fact that we revealed in our study that polygamous mating in Eurasian lynxes is not rare and was documented for both sexes. Adult male lynxes were found to commonly mate with two or even three females with some time lag in between mating, during the mating season in the second half of February till the middle of April (at least 8 precise registrations).  Females sometimes mated with two males, intersected with some time lag (2 precise registrations).

Coming back to the plausible aspect of adult males taking part in family life, I would like to state that in our gained data, the majority of the traced lynx mothers with litters were under at least some care of an adult male. Such an adult male was frequently registered in the close proximity to the mother lynx with kittens in May-October. Surely, that was not just an irregular interest of the adult males to the presence of mother with kittens in his home range, because males were registered too close to the females with kittens and too often. At least, we assume that adult males protected the family house areas by local intensive marking and territorial calls. Just in May and June we found the third well-marked increase in lynx territorial calls from trees. Remarkedly, that such adult male behaviour was registered mainly in the areas where lynx family groups stayed (5 such areas were traced for this behavior). There is another evident question. Does an adult male lynx bring food to a family or maybe he takes part in the hunting activities of the mother? Those questions are still entirely unknown. Also, perhaps sometimes an adult male lynx stays with the kittens and guards them (why not?) – that is still a searchless question, too.

At the left and center you see lynxes at the trees of their territorial calls in May (just after jumping down from the trees). At the right you see adult male lynx is calling from the declined tree in the early June.

Another relative question is, where do lynx kittens mostly stay after the early denning period, when their mother is gone for foraging. We numerically registered kittens staying at abandoned or nearly abandoned badger setts for a few days or even up to almost a month (17 registrations). We documented them in treefalls (3 registrations) or in thickets from fern-young spruce or willow-hop or just high grassstand on a small forest glade (altogether 7 registrations). But such documentations are seemingly not sufficiently frequent in relation to our high efforts to reveal this and the rather high density of lynxes (up to 6 inds per 100 km² in winter) and the many family groups in the study area in Naliboki Forest. I assume that in July-October, lynx families mainly (for 70-90%?) use another type of sheltered (from wolves, wild ungulates, mosquitos and flies) spots for stay (resting then may be combined with the mother’s ambush hunting). That is, trees with some kind of branch platform, in particular when one tree is inclined on another tree, preferably if the trees are spruces. Quite often there is like a real comfortable platform at the point, where the trees touch each other. There, a lynx family may couch.

Perhaps, sheltering of kittens on such a tree-based platform is the reason of their rather high survival, for instance, compared with wolf pups. Indeed, till winter usually approximately 40 to 60% and even up to 90% of wolf pups die (Sidorovich and Rotenko, 2019). Wolf pups were documented to be killed by lynxes and trampled by wild ungulates for a number of cases. At the same time, lynx kittens are rather good survivors. We are not ready to assess lynx kitten survivorship still, but we may already say that, for instance, in Naliboki Forest in Belarus, lynx kitten survival is not lower than 80% till winter and 60% till May. It means that the mortality in lynx kittens is usually 2-3 fold lower and even up to 5 fold lower than that in wolf pups. There should be a clear reason for that. It looks like staying a lot on a tree height is the reason, but that should be proved by plenty of registrations. We are still pressed for a sufficient amount of such registrations.

At the left mother lynx with kittens in treefall. At the right lynx kittens staying at abandoned log pile.

From telemetry on lynxes I know that during summer, both sexes of the species use several small house areas, where they stay the main part of their time, while the other parts of their home ranges are rather seldom visited by them (Sidorovich et al., 2018). Despite of the fact that we discovered many such lynx house areas that were used during the warm season, it could be too self-confident to point out the particular habitat types, which lynxes prefer, even by following the telemetry (including GPS GSM) data because of the great habitat heterogeneity of the forested terrain we investigated lynxes in Belarus. Such data in relation to the habitat usage by lynxes during the warm season were published from several studies. But even in the case of GPS GSM it’s hard to believe that the gained data is accurate enough to reveal relevant information on micro habitat usage, if the forested terrain is not too homogeneous. Under the data accuracy I mean a correspondence between the fixed coordinates and the particular spot lynx actually used. Having even top-quality expensive transmitters, we did not find such a sufficient accuracy in our very heterogenous terrain. So, we believe that the habitat types which lynxes (separately different lone individuals and family groups, at least) actually prefer during the warm season is still a much unknown question. We assume that it is correct to study on this topic only by means of extensive camera-trapping. From the preliminary data that were obtained on the question it looks like not only presence of some types of habitats in lynx house area plays an important role , but first of all the specific situations that provides sufficient availability of suitable prey (Sidorovich et al., 2018) and beneficial habitat package that favors easy foraging. However, in our case it is still more hypotheses than clear results, so, this demands a lot of further study.

Perhaps, during the warm season, lynxes provide in their diets easily by catching young prey (that is a question at the same time). Here the main pressing question is, how often in the warm season the staying of a lynx in a particular point is actually ambush hunting and how often that is just resting with sleeping. Our (still small) gained data on the question suggest that it is about three fourths ambush hunting, but anyway during warm season, lynxes sleep seemingly more than in the cold season.

A relative question is , how often is such a point situated on a tree height. By applying up to 70 camera traps and registering lynx footprints, hair and claw marks, we found staying of lynxes in many spots at the ground level such as treefall, burrows of wolves, badger and even beaver and tall grass stand. Also, lynxes tend to groom on open sand spots. Nevertheless, the too low frequency of lynx registrations in such spots compared to the rather high lynx population density in the main study area in Naliboki Forest (3-6 inds per 100 km²) suggested again that mainly they stay somehow on trees. That is very reasonable, because, by staying on a tree in a relevant point, lynxes combine ambush hunting with avoiding aggression of wolves and ungulates (it is rather important in the case of kittens) and avoiding of mosquitos and flies.

Ok, but that is a consistency merely. Such a hypothesis should be proved on large enough materials. We started gaining such a material by means of lynx claw mark registration on trunks as well as by camera-trapping. As to applying camera traps, there are problems on the way. Being at a marking point, normally lynxes do not react on a presence of camera trap, and there is not any problem to register all the lynx behavior at marking point. Quite opposite, we noticed that at a point where a lynx is staying it is rather sensible to the noise of camera working and even on the presence of camera trap itself. In effect, they often escape and even do not come back to the spot. Not all lynxes behave like that, but it is fairly often..

Coming back to the usage of trees as a spot of staying, I would like to notice that still our dataset is not large enough, but the registrations we made suggest that the tree-staying hypothesis seems to be right. Such a point of lynx staying on a tree height in the warm season seems to be characterized by a lot distinctive features compared to those of the trees applied by lynxes for territorial and mating calls. Respectively, the question is, what are the traits of such ambush hunting-resting trees and their adjoining habitats? In our case, we still have a too small sample size to analyze that in details. Two evident traits are surely known. Such spots on trees should have some kind of sitting platform and should be situated nearby the potential prey pathway or their foraging place. Concerning the other small questions, it is curious to know which factor actually drives the tree-related stay of lynxes in warm season: the easier hunting (detecting of prey on a relevant distance) or avoidance of mosquitos and fly attacks? Concerning the above we guess that lynx mother with kittens try to stay on tree height as much as possible (to save kittens), whereas adult males stay there, when there are too many mosquitos and flies.

Mother lynx with kittens and adult male lynx in the same spot on the declined tree

Lynxes are grooming on open sand spots

Also, one of the question is how often lynxes are actually outside of their small house areas during the warm season and for which needs are they there? Here it is important to explain why lynxes are generally reluctant to mark their home ranges, perhaps, with the exception of adult male marking of house areas of family groups.