Trends in the denning behaviour of the wolf and lynx in connection with the changes in the vertebrate community in Naliboki Forest (north-western Belarus)

By investigating the denning behaviour and ecology of wolves (Sidorovich and Rotenko, 2018) and lynxes in Naliboki Forest, we faced with several evident trends during the last years (2016-2018) that we connect with the changes in the local vertebrate community or  more specifically with the pronounced changes in the population densities of those species  that may affect the denning conditions for wolves and  lynxes.

Under “we” I mean me and my collaborators, who helped me in this study, first of all, Irina Rotenko from Naust Eco station and Jan Gouwy from Wild Naliboki team as well as other collaborators from this team  (Maximillian Hezter and Sanne Ruyts), who assisted markedly, too.

The first change in the vertebrate community was a significant increase in the number of bison, elk and red deer. These animals are usually aggressive towards wolf pups and wolf denning in general (Sidorovich and Rotenko, 2019). Usually they trample wolf pups, when they faced with them. In the spring of 2018, there were no fewer than 100 bison in Naliboki Forest, and approximately 200-900 red deer including 20-50 big aggressive stags per 100 km² and 40-80 elks per 100 km². During May-July these wild ungulates use treefalls and other thickets a lot for either giving birth or keeping small calves or sheltering from attacks of abundance of blood-sucking insects. Thus, wolf breeders nearly lost treefalls and other thickets as a quiet and safe place for denning and raising pups. Concerning lynx denning in treefalls, mother lynx still could keep kittens on a height of inclined trees there, and danger from wild ungulates is not so important in this case. The most essential situation for denning by lynxes is to have wolves rare in occurrence in the proximity to kittens.

Second, in Naliboki Forest in 2018 the population density of lynxes greatly increased up to almost five individuals per 100 km². This rather high density of lynxes was plausibly determined by very favourable habitat conditions in Naliboki Forest. There are still many old forest patches and simultaneously many clearcuts, whereas most of the numerous drainage canals are blocked by beaver dams. All such habitats are densely inhabited by suitable prey for lynxes (e.g. roe deer, red deer, beavers, hares, grouses and ducks).

Photo by Vintses' Sidorovich
Lynx male at marking point. Recent photo by Vintses’ Sidorovich


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Also, during the last decade, up to ten brown bears appeared in Naliboki Forest, and that plausibly has a negative impact on wolf denning as well.

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Also, adult lynxes tend to deliberately hunt wolf pups and kill heavily pregnant female wolves. In effect of the strong negative impact of wild ungulates and lynxes on wolf reproduction, wolves began denning in burrow exclusively. While denning, they enlarged red fox earths and badger outliers as well as dug burrows themselves, whereas denning on an open couches in treefalls got rare in occurrence. Anyway, the reproduction in wolves almost stopped in Naliboki Forest because of too high mortality of pups, and the number of wolves decreased markedly. In this period with unfavourable conditions for wolf reproduction in Naliboki Forest, the mortality in wolf pups before their first winter increased to over 90% (Sidorovich and Rotenko, 2019). As a consequence of Naliboki Forest being so densely populated by animals that pose a threat to wolf denning, a part of breeding wolves even emigrated outside of the forest massive for denning, in order to save their pups. In 2018 we traced two such wolf breeders, which emigrated from the forest to its edge with vast maize field, and they denned and raised pups there. So, the decline in wolves and their leaving of treefalls in breeding time liberated these sheltered habitats for denning of lynxes.





In Naliboki Forest we have already noticed this trend (i.e. emigration of breeding units of wolves before denning) in 2016 and 2017 (Sidorovich and Rotenko, 2018). However, in May 2016 and 2017 it was not so pronounced as in May 2018, when only one (maximum four) breeding group of wolves out of more than 20 wolf breeding units registered in late March and early April remained in the forest massive for denning.


We are sure of these results. From two to five of us worked for 40 days since the end of April until the 8th of June, and we discovered only 9 dens from one wolf breeding group consisting of two breeding females and one male. Before the -unfavourable situation for wolf denning described above, we (one to three of us) worked for 25-30 days and found several hundreds of wolf dens including 2 to 5 actual ones i.e. with pups. At that time there were usually only 8-13 wolf breeding groups in mid-April.

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Several trends were noticed in the denning behaviour of wolves in the new unfavourable situation in Naliboki Forest. The first one is the new unfavourable situation in Naliboki Forest is emigration of breeders out of Naliboki Forest to den in the forest-agriculture mosaic surrounding the forest massive. There the majority of residential wolves are killed each winter during the species population control actions. Intensive camera-trapping in Naliboki Forest in 2015-2017 suggests that, at least, a part of such emigrated breeders comes back to their previous territories in the next autumn, but still it is hard to say what the reproductive efficiency of such breeders is. Actually, we documented only two, maybe three such cases (wolves are not easily recognisable by camera-trapping), and in one of the cases the returned pack of nine wolves had 3 or 4 pups of the biological year.

Some breeding sites of such emigrated wolf breeders were outstandingly interesting. For instance, in July-August 2019 a wolf family with pups stayed in the large maize field on the distance about one kilometer from the forest edge and not faraway from petrol station.

The second trend in the denning by wolves in Naliboki Forest is the increasing use of pine stands as a main denning habitat type. During the first decade of the 2000’s and early 2010’s only about  6%  of the wolf dens, which were found by us (mostly without pups, recent ones, n=736 dens), were situated in pine stands. Quite opposite, in the new unfavourable situation for wolf denning in Naliboki Forest since 2016,  about 52% of the wolf dens, which were registered by us (n= 104, again mostly without pups, recent ones), were found in pine stands. This switch in the used denning habitats by wolves may be explained merely by potentially less disturbance of breeding wolves by lynxes and wild ungulates in pine stands, because these habitats are poor in food and poorly structured and thus markedly less frequently used by species that are hazardous to denning wolves.

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Another evident trend in the wolf denning behaviour in Naliboki Forest is the increasing use of burrows to place pups during their first days, perhaps, as an attempt to save the pups from attacks of the above-mentioned inimical animals,  first of all, the lynx.  Before the new situation in Naliboki Forest breeding wolves mostly used open couch-dens. These dens were not so easily noticeable for the inimical animals, and when too many mosquitos or too much smell accumulated at such a couch-den, the parent wolves easily relocated the pups in a new couch-den. Perhaps, it was also essential that not much effort was needed to prepare a new simple couch-den. Usually such couch-dens were situated in treefall.   In the first decade of the 2000s and early 2010s, 72% of the  wolf dens, which were found by us  in Naliboki Forest (mostly without pups, recent ones, n=736 dens), were found in treefalls. Quite opposite in the new unfavourable situation for wolf denning in Naliboki Forest since 2016, about 68% of the  wolf dens, which were registered by us (n= 104, again mostly without pups, recent ones), were burrows or cavity-dens.

Quite often when wolves prepare a burrow-den, they do so by enlarging the entrance of a badger sett or red fox earth. This means there are still plenty of narrow passages, made by the former owners (badgers or foxes), where the wolf pups (or at least, a part of them) may escape  in the case of a lynx attack; see the photos below.

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It happened the fast recovery of the badger population during the last 7-9 years in Naliboki Forest, favoured by a simultaneous decline in raccoon dogs. The decline of the local raccoon dog population was initiated by a heavy infestation of Alaria alata helminths and scab mange. Afterwards, the decline of the raccoon dog population was exacerbated a lot by heavy predation of lynxes and wolves. Here it is important to mention that solely the impact of raccoon dog was the main cause of the strong population decline in badgers in the previous decades (Rotenko and Sidorovich, 2017). After the raccoon dogs got relatively low population density in Naliboki Forest, the recovered local population of badgers occupied not only all former badger setts, but also all present red fox earths, former wolf burrows and even abandoned beaver burrow networks in sandy banks of drainage canals.

Moreover, a badger is a fairly strong animal, and at its sett it feels quite secure. Of course, we have got many registrations of small badgers being killed by lynxes and wolves at their setts or at a further distance, but even an adult wolf will not venture to attack a big badger at its sett. Furthermore, badgers live in families, which can get quite large. A pregnant female lynx might be able to kill one badger with a lot of effort, but to kill the entire family, including a big male, would be too hard. So, the number of relevant vacant burrows for lynx denning declined considerably, because nearly all burrows suitable for lynx denning were occupied by badgers.

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Of course, increased number of burrows of badgers can be favourable for wolf breeders. Nevertheless,  such a subterrestrial den of breeding wolves doesn’t offer full protection for their pups from lynx attacks. However, for the lynx, entering such a burrow-den, it is rather risky, because the parent wolves may be nearby and attack the entering lynx. Such a lynx may be killed by them or, at least, injured severely and die afterwards from its wounds.

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In 2014-2018 we registered several lynx attacks on wolf dens in the Rabachova locality of Naliboki Forest and documented the behavioural responses of those  breeding wolves.  During four breeding seasons (2014-2017) the breeding group of wolves (two to three breeding females and one to two adult males, both not small ones) had lost all their pups already somewhen before  early autumn, despite the fact that in April-May of each these years there were one to three litters in the breeding group. In late  April 2016, by reading the activity signs from the local wolves and lynxes, we got more or less convinced that, at least, one wolf litter was killed by a male lynx.

In early May 2017  (on the 5th and 11th), the same male lynx killed two litters from the wolf breeding group for sure. We succeeded to document these events (e.g. see above photos from the Rabachova locality of Naliboki Forest). Several days after the second litter was killed, the third litter had disappeared as well, and the most plausible explanation is that this third litter was killed by the same male lynx, too. Similarly, we are almost sure that the unsuccessful breeding of the wolf group in 2014 and 2015 was because of attacks of the same or another lynx.

In the denning season of 2018 the same wolf breeding group started preparing dens in mid-April in the Rabachova locality again, but then, after facing with lynx presence in the denning habitats and after the experiences of lynxes killing their pups during previous breeding seasons, they seemed to escape out of the forest massive.  Suddenly, after much preparations for denning they just disappeared. We undertook a lot of efforts to find the new denning locations of the wolves, but we didn’t find anything that suggested new attempts to den inside the forest.

Concerning the denning behaviour of lynxes and its new trend in Naliboki Forest, it is quite complicated and there are still a lot of uncertainties, but we find it necessary to mention the new features we have learnt and to present the results and ideas that we obtained so far.

From the all sources of information, which  we gained on the denning of lynxes in Naliboki Forest and the whole Belarus till 2017 (see  “Where do births and raising early days kittens in lynxes take place? When do lynxes give birth in Belarus? “),we assumed that burrows were the main type of dens for lynx kittens during their first days, at least. At the same time, parturition somewhere under treefall or in a thicket was quite rare. Indeed, during twenty years of searching for wolf dens in Paazierre Forest and Naliboki Forest in Belarus in April-June in 1997-2017 I have found more than one thousand of wolf dens (mostly without pups, former ones) under treefall and other thickets (mainly young spruce thickets), but only a few lynx denning sites (easily recognizable by the presence of lynx hair) have been found under inspected treefall.

However, that was before the fast recovery of the badger population. By 2018, badgers reached a high population density in Naliboki Forest and recolonized all their former setts and occupied almost all former wolf burrows, abandoned beaver burrow networks in sandy  banks of canals and red fox earths. Under these conditions, pregnant female lynxes were facing a lack of well-sheltered refuges to give birth and raise kittens during their first days. On the other hand, as described above, the majority of breeding wolves emigrated from Naliboki Forest to give birth and raise pups.   Under these conditions, it seemed that adult female lynxes began denning in treefall and other thickets markedly more than before.

Female lynx is checking the former wolf burrow-den may be with the purpose of denning there, but the burrow is occupied by badgers nowadays
Female lynx is checking the former wolf burrow-den may be with the purpose of denning there, but the burrow is occupied by badgers nowadays

In effect, in May and early June of 2018, while searching for denning by lynxes in treefalls and at fallen trees, we discovered three lynx lairs in Naliboki Forest during 40 days of searching. The first lynx lair looked like a couch, which was situated in a dense treefall; the lair spot was in a thicket of tree materials and raspberry bushes at a root plate of uprooted spruce. The second lynx lair was dug by the mother under a thick trunk of fallen huge pine at its root plate. The lair looks like a round cavity about 50-60 cm in diameter. The third lynx den in kind of a well-sheltered couch was found in a boggy pine stand with dense Ledum palustre shrub and a small former clearcut with a lot of abandoned logs and rotten log piles.

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