In the scientific literature about brown bears Ursus arctos and wolves Canis lupus there is information on the interactions of the species. Nevertheless, facing that denning in wolves is so insufficiently investigated (Sidorovich and Rotenko, 2017, 2019), it is easily believed that possible interference of brown bears towards wolves at denning is unknown still.
In Naliboki Forest in north-western Belarus we carried out quite a lot of studies on wolf breeding (Sidorovich and Rotenko, 2017, 2019), but that was mainly in the conditions of absence of brown bears or presence of a few bears in the habitats. Only during the last two years (2018 and 2019) brown bears became more or less common in Naliboki Forest (https://sidorovich.blog/2018/10/07/story-of-the-brown-bear-in-naliboki-forest-and-the-peculiarity-of-the-on-going-recolonizing-of-the-terrain-by-the-species/), and it appeared possible to investigate the interspecific interactions of brown bears and wolves and particularly during denning period in wolves.
The first information that was gathered on the question in Naliboki Forest suggested an importance of avoiding of bear aggression by wolves at denning to save pups. On the other hand, bears look like tending to persecute parent wolves at denning as well as try to kill their pups. In this post I just mention about the documentations and observations we (Naust Eco Station and Wild Naliboki) succeeded to get during these two years.
In the second half of May 2019 in Naliboki Forest we registered of very plausible killing of wolf pups in den by brown bear. Two brown bears (mating couple) frequently followed the wolf couple at denning, they inspected their dens, and finally the wolf litter has disappeared.
In May-June of 2018 in Naliboki Forest again we registered similar behaviour of another adult male bear to another wolf breeders.
Moreover, in July-September of 2018 in Naliboki Forest we documented regular visiting of homesite of another wolf family by another male bear. The bear marked that place a lot in three points. Interestingly, that in May-July of 2019 the bear was present at that place again, but did not mark all the three points, when there was no regular stay of breeding wolves in the place.
All these already suggest possible heavy interference between bears and wolves at denning and raising pups in homesites, but still it is a little known about the question.