Co-author Irina Rotenko
During 2023, we continued our long-term studies on the wolf reproduction in Naliboki Forest (see Sidorovich and Rotenko, 2019 and other posts in this blog for details and more information). An outstanding feature of this year for the reproduction of wolves in Naliboki Forest was the relatively low number of lynxes (15-20 individuals). This is 4-5 times lower than that in 2016-2018. Lynx is one of the hostile species for wolf pups (Sidorovich and Rotenko, 2019; Sidorovich, 2022), and presumably killing of wolf pups by lynxes can nullify the breeding efforts of wolves. However, there are other hostile animals to wolf reproduction such as brown bear, bison, elk and red deer, sometimes wild boar and even red fox (Sidorovich and Rotenko, 2019; Sidorovich, 2022). Therefore, we still could not test the hypothesis of which of these antagonistic species plays the main role in killing of wolf pups. This year gave us a unique opportunity to examine the role of lynxes.
This year, we worked with wolves in their denning areas and home areas of families with free-ranging pups in two thirds of Naliboki Forest, which covers about two thousand square kilometers. We used 30-45 camera-traps, and obtained slightly more than two thousand videos (20 seconds long) and photos of wolf pups, their parents and pup-sitters. We also conducted a lot of habitat inspections and searched for wolf dens (see the method used in Sidorovich and Rotenko, 2019 or in Sidorovich, 2021) and traced wolf families in their home areas, where wolf parents stay with free-ranging pups for a relatively long time. Pack multi-breeding was revealed by registering either several dens with differently aged pups at a relatively small distance of up to 3 km, usually less than one km; or two or more mothers in the same small area (up to 3 square km) on the same days; or a group of differently aged pups that stayed together or in the same small area (up to 3 square km) on the same days.
You can support the research on large carnivores in Naliboki Forest by buying just a coffee. It will help to keep the study going.
Below, we share the main results of our study on wolf reproduction in Naliboki Forest in 2023, which will be given as a brief outline:
(1) We documented two situations of pack double-breeding and one situation of pack triple-breeding. Single breeding, i.e. just a breeding couple, was revealed in two cases. So, a total of nine wolf litters were registered in Naliboki Forest. Two wolf litters were born very early (late February to mid-March); the other seven litters were born in a normal season (from mid-April to mid-May).
Concerning the registered too early denning in wolves, we would like to say that it is not the first year we found this phenomenon. We registered it for nine times in total.
Hypothetically, we connect this trend with more intensive hybridization of wolves with stray dogs that has been happening since 2010, and we do not see any other cause that could affect the timing of wolf breeding in Belarus so dramatically. It seems like nowadays in Belarus, wolves are genetically polluted by on-going hybridization with stray dogs, while two decades ago wolves were almost unpolluted in the country. In the early 2000s, we sampled wolves in Belarus for a genetic study, and none of these wolves showed any dog ancestry (Stronen et al., 2013).
Concerning the two cases of abnormally early breeding that were found in 2023, it is worthwhile to notice that both mothers and fathers of the litters looked like normal wolves.
In the photo below, you see an early (late February) born wolf pup in the mid-June. Another female from the same pack gave birth in the same denning area in the late April. In the photo-gallery below, you see the pups in the mid-June, too.
In the photo-gallery above, you see resting sites of a heavily pregnant female wolf. It is quite an interesting case that she waited to give birth at the prepared burrow-den for about a week. In the place, there were seven such trampled resting sites.
(2) In 2023, all the wolf breeders continued using only burrow-dens; and help of pup-sitters was largely used. There were pup-sitters (one, one and two) in all three wolf breeding groups that were traced by us in detail. From the posts we have already published before and the book (Sidorovich and Rotenko, 2019), you may learn that we evaluate these breeding behavioral traits as adaptations to breed under the conditions, when breeding-hostile animals are common in habitats.
(3) In 2023, under the conditions of relatively low density of lynxes, wolf pup mortality was not as high as before, when there were 3-5 lynxes per 100 square km. When lynxes were so common, usually from 7 to 9 out of each 10 pups died (mainly were killed) until the first winter (see other annual reports in this blog for details). In 2023, we are not able to estimate pup mortality precisely, but we can say that it is considerably lower than before. Only one litter disappeared; presumably it was killed by an adult male lynx, which was registered around the wolf den for several times. In other eight litters, from 2 to 7, on average around 4 pups survived until November. We roughly estimated that in 2023, wolf pup mortality was around 50%. This result suggests us that lynx plays a major role in extermination of wolf pups, while bear, bison, elk and red deer (stags) and others are of secondary importance.
(4) Based on a large amount of photo- and video-registrations of wolf pups, we would like to report that in the post-denning period from the mid-June to the end of August, wolf pups are active against each other (run after, tussle, fight) for 82% of the time. This estimate is more or less accurate, as we placed camera-traps not only at playgrounds but also in resting places in an equal proportion more or less. The sense of such an adversarial position of pups is to establish some hierarchy between pups, and a pup with higher rank usually takes food first, when parents bring food. The obtained footage supports this inference a lot.
Below, you can see some footage taken by us in 2023.
You can support the research on large carnivores in Naliboki Forest by buying just a coffee. It will help to keep the study going.
Zoology by Vadim Sidorovich 
I wonder what might be the reason for the relatively lower lynx density in 2023 compared to previous years?
A disease, possibly Feline Immunodeficiency Virus https://wordpress.com/post/sidorovich.blog/4789
(Sidorovich, 2022)
Thank you, Mr. Sidorovich
Do you see a cyclical nature of the lynx population due to natural factors like the ones Canada Lynx follows? I know Eurasian lynx aren’t as dependent on one single prey species like Canada Lynx which means they shouldn’t vary as much, but I know you mentioned that long winters played a role on roe deer survival, which I would guess played a role on Eurasian Lynx kitten survival with a one-year time lag. Is this the case?
I know you also mentioned that wolves generally don’t kill Eurasian Lynx kittens and their interspecific competition for prey isn’t too large, but could their populations be intertwined negatively (when there are a lot of wolves, Eurasian Lynx decreases, when Eurasian Lynx increases, wolves decrease)?
Thank you for your amazing work as always. Awaiting your reply.
Thanks for the questions. Demographically the Eurasian lynx has problem of surviving of subadults, when the optimal prey species are scarce (roe deer, hares and tetraonids), while kittens staying with the mother survive rather well anyway. For me it is hard to say about cycling in the Eurasian lynx population. Historically maybe such cycles happened, but in the modern world with the diverse and strong human impacts, possible cyclic nature of the lynx population is of secondary importance anyway. The last four decades during which I was more or less involved in the tracing of the lynx population in Belarus or in a particular forest in the country, I noticed two main driving factors: first, extermination of lynxes by hunters (poaching mainly), and second, impact of a disease (in Naliboki forest the lynx population was supressed by a disease since 2020) .
At least, in Naliboki Forest lynxes markedly supressed the wolf population by frequent killing of wolf pups and lonely staying subadults sometimes. Wolves only limit usage by lynxes open habitats.
Dear Vadim, I would like to know relationship betveen wolfs and vipers(vipera berus). Is sneak bite poisonous for wolves? Is it dangerous for wolf pups, when they are bit by snake? How often it happen by your oppinion, that snake bite a wolf. Thanks for answer.
Dear Milan, thanks for the interesting question. I have never faced with such cases but assume that it happens sometimes particularly with wolf pups. We keep a pet wolf-dog hybrid, and when the hybrid was young, it attacked adders. It was bitten by an adder, and we have rescued it. Since that accident the hybrid began avoiding adders as well as other snakes. Best wishes, Vadim