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 local vertebrate community is that during the last years, Naliboki Forest (about 1900 km2  and with surroundings 2750 km2 ) appeared to be densely populated by lynxes (since 2015 more than 40 inds, in 2018 more than 80 inds, see the below lynx distribution map). In 2018, the lynx population density in Naliboki Forest constituted about 5 inds 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 roe deer, red deer, beavers, hares, grouses and ducks, and these animals are suitable prey for lynxes.

Adult lynxes tend to deliberately hunt wolf pups and kill heavily pregnant female wolves (see “Mortality in wolf pups”); and in effect, the reproduction in wolves may stop, which has already happened in Naliboki Forest (Sidorovich and Rotenko, 2018).

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

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The second change is that during 2015-2018 the number of other vertebrate animals such as bison, elk and stags (i.e. relatively big red deer males) increased markedly in Naliboki Forest. These animals are usually aggressive towards wolf pups and wolf denning in general (see “Mortality in wolf pups”). In the spring of 2018, there were not fewer than 100 bison in Naliboki Forest, and approximately 20-50 stags per 100 km² and 40-80 elks per 100 km².

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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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In these unfavourable conditions for wolf reproduction in Naliboki Forest the mortality in wolf pups until their first winter became higher than 90% (see “Mortality in wolf pups”), and in turn, the wolf packs began consisting mainly of adults. Also, despite almost a double decrease of the wolf numbers in the forest,  the number of breeding units (couple or larger group of breeding wolves) markedly increased – approximately 18-24 breeding units in the last years versus 7-13 before. Nevertheless, during the last denning seasons only a small part or even only a few of such breeders stayed in the forest for denning and raising of small pups (e.g. see the below wolf distribution maps from the last winter and spring of 2018). The majority of wolf breeders seemingly emigrated outside of the forest massive for denning, in order to save their pups, because Naliboki Forest is densely populated by animals inimical to wolf denning.

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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.

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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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Thus, the first trend in wolf denning behaviour in 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.

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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However, during the last 7-9 years we registered a rather fast recovery of the badger population in Naliboki Forest, in the background of the decline in raccoon dogs. The decline of the local raccoon dog population was initiated by a heavy infestation of Alaria alata  helmints and scrab mange. Afterwards, the decline of the raccoon dog  population  was exacerbated a lot by heavy predation of lynxes and wolves. 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. Interestingly, that breeding wolves visiting their burrow dens from the previous year, which were newly occupied by badgers, were not much aggressive towards the new owners (see the photo below).

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Of course, 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 we discovered three lynx dens in Naliboki Forest during 40 days of working:

two dens under dense treefall with several layers of fallen trees, partly overgrown with young trees;

one den  in a boggy pine stand with dense Ledum palustre shrub and a small former clearcut with a lot of abandoned logs and log piles.

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