Co-authors: Irina Rotenko and Gerard Oonk
In the last year after our study on denning in wolves in May 2020 we have already reported about the peculiar situation in denning by wolves in Naliboki Forest, the central-western Belarus. Wolf breeders stopped denning on open coaches as it used to be, and they began denning in burrows exclusively, when mammals (red deer, bison, elk, lynx, brown bear), which are characterized by aggressive behaviour to pups, got plenty altogether in this forested terrain.
In May 2021 we discovered four active wolf dens and traced the denning behaviour of two wolf breeding groups having two and three breeding females (both cases of a multi-breeding in a wolf pack). All the five breeding female wolves kept pups in burrows only. Altogether we found 33 wolf burrow-dens that were used for denning: 7 self-made by wolves and 26 enlarged badger-setts and outliers. Interestingly, that 11 out of 26 badger burrows were wolf burrow-dens before (2-7 years ago). No any wolf couch-dens were found in May 2021, while before such a situation that is inimical for wolf denning they denned on open couches and pits.
See the video below for the details of denning in wolves in Naliboki Forest during May 2021.
Zoology by Vadim Sidorovich 
Are you sure the parents didn’t move the pups to a new location before the bear destroyed the den?
In USA wolves live in packs, and they will fight to protect pups and dens and each other from brown bears. Why are wolves living and breeding as pairs in your area? Is there not enough game to feed a pack?
Thanks for the questions.
First, a general thing to get you know. In North America and in Eurasia wolves are so distinctive. In my point of view as well as other known wolf specialists they are definitely like two different species, particularly behaviourally. There are many essential reasons for that inference. Please, read our monograph on reproduction in grey wolves in Belarus: common belief versus reality (Sidorovich & Rotenko, 2019) as well as some literature of other wolf researchers cited therein.
In Belarus and adjacent areas (perhaps in the whole Eurasia) in denning period (mainly since the late April till the mid-July) breeding wolves mainly live by a breeding couple or by a larger group of breeders and pup-sitters sometimes (the case of multi-breeding). Real packs exist since October till the mid-April.
Concerning the pups in the burrow-den that was destroyed by the bear, yes, the pups were in the burrow-den in the moment the bear came as well as the parent wolves were nearby. The parents approached the destroyed den just after the bear left it. But they were afraid to attack the bear, they even were afraid to search for pups under sand that moment. Nevertheless, they visited the destroyed burrow-den three next nights and dug there a lot. When we appeared at the den afterwards, all the den spot was dug by the parent wolves. It was so evident that they tried to find pups under sand so much.