Coauthor Irina Rotenko
Warm-season and in particular summer behaviour and ecology in Eurasian lynxes is fairly unknown. During the last two warm seasons (April-October 2019 and 2020) in Naliboki Forest, central-western Belarus we advanced in investigating of this topic.
Concerning the additional information in relation to denning in lynxes, during the last two warm seasons there were found four denning plots with several lairs (recent ones and actual lair in one case) in each plot. One denning plot (May 2019) was situated in old broad-leaved deciduous forest in the valley of Biarezina medium-sized river. All three used lairs were in big hollows of fallen huge oaks and lime with rotten boons. Kitten chamber was situated 2-4 meters deep inside.
Denning of another female lynx in May 2019 took place on large island that was created by split of small river of Vol’ka. The denning spot was in old spruce forest with some fallen huge spruces that were semi-rotten already. All three recent lairs were placed in cavities under butts of fallen spruces at their root plates.
In the late May and early June 2020 two female lynxes denned similarly in treefalls of mixed spruce and small-leaved deciduous forest with some birches and spruces left. There were 3 and 4 recent lairs in each denning plots. All of them were placed in uprooted big trees (aspens and birches). The kitten chambers were under butts or in the spot where the broken root plate made like a cavity-den that had only small or no holes outside. Mother lynx dug small entrance into the cavity. These two mothers with kittens used the treefall areas of one to 2 square km during the whole summer and early autumn.
Additionally in May 2020 another heavily pregnant female lynx inspected former wolf burrow-dens and badger setts, perhaps, with the aim to den therein. Nevertheless, finally she gave birth in another unknown site.
As to the two breeding female lynxes we could trace, since late April till the mid-July adult male lynxes were tensely scratch marking in both denning areas. Mainly they made ground scratch marks. Also, the adult males were registered a lot by our camera traps in the close proximity to the mothers with kittens. For several times we registered calling by the adult males as well as voice-to-voice communication between the mother and adult male at the distance not larger than 30 meters. In our registrations there are much support that both of these adult males are the fathers of the kittens. However, still we did not document those adult males together with the mother and kittens.
Hypothetically we expected that kittens most of the time should stay alone, whereas their mothers hunt. Actually, we obtained quite opposite results. There were surprisingly many registrations that mother lynxes were most of the time with kittens and only once we registered that one mother was absent for several hours. That indirectly suggests that maybe the adult males help mothers with foraging for their kittens. However, besides of this speculation we still have no any proof for the idea.
Thus, for the moment according to out camera-trap registrations, we already got convinced that adult male (possibly father), at least, protects homesite of family by scratch marking, sound marking and just by his frequent presence nearby. Additionally to the filming by camera-traps, our registrations of lynx territorial calls (mainly by signs of climbing tall trees) are relatively often just since the late April till early July i.e. in the denning season of lynxes.
Concerning of raising of kittens during the two warm seasons we registered small lynx kittens in badger setts for five times: twice by camera-traps and for three times with tracks.
Another interesting question is rather high kitten survival during the warm season in connection with tree-related staying of kittens. At present, we gained sufficient amount of registrations that in the warm season since July lynx kittens stay really a lot on trees. Although such trees can be standing ones, but kittens prefer to stay on inclined trees and fully fallen ones. Even staying of kittens on fallen trees at the height of 1.5-2 meters saves them from attacks of red deer, elks, wolves and brown bears, taking into account great mobility of lynx kittens. Using tree-based platform, where one tree inclined on another one, plays a marked role in safety of kittens, too. Such behaviour of lynx family with sheltering kittens on trees (standing or inclined or fallen) is actually the reason of their rather high survivorship, 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 definitely say that, for instance, in Naliboki Forest in Belarus, lynx kitten survivorship 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 sometimes even up to 5 fold lower than that in wolf pups.
Another important finding deals with traits of warm-season homesites of lynxes, where they stay most of the time. From telemetry on lynxes in Paazierre Forest in northern Belarus we 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). Nevertheless, by basing on the telemetry data, we could not reveal such crucial habitat traits, because we were in doubt with the telemetry data accuracy in the conditions of highly heterogeneous landscape.
To investigate the question in the terrain of Naliboki Forest, we spent a lot of efforts with camera trapping, habitat inspection as well as we checked on which prey species lynxes rely actually during their warm-season staying in small homesites. All the studied cases suggest that among lynx warm-season habitat demands in Naliboki Forest there are three almost equally important traits. The first and second traits are simultaneous sufficient supply with two beneficial prey species such as roe deer and beaver. The third trait is presence of old forest with at least some treefall or many sporadically distributed fallen trees. In the terrain of Naliboki Forest the above three traits come into habitat reality basically as following. First, it is some ecologically rich part of river valleys (old forest with many fallen trees as well as abundance of roe deer and beavers). Also, it may be forest drainage system that densely occupied by beavers and roe deer and having treefalls. Another ecological situation is drained grassy opening with treefalls nearby (not further 2 km).
Still an important question of summer behaviour and ecology of lynxes is , how often they stay with ambush hunting 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.
During the two last warm seasons 2019 and 2020 we advanced in studying of the question quite a lot. But still we are pressed for initial data to do circumstantial analysis of this behaviour of lynxes.
Despite of our current dataset is not large enough still, but the registrations we made suggest that the hypothesis of tree-staying of lynxes during summer 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.
Lynxes are grooming on open sand spots, where there are fewer blood-sucking insects.