Co-author Irina Rotenko
Every May we continue our long-term study on behaviour and ecology of denning wolves. Since 2004 the terrain of Naliboki Forest (the central-western part of Belarus) has been the main study area for the question. Since 2018 the brown bear has become more or less common there. It appears possible to investigate the interspecific interactions of brown bears and wolves and particularly during denning period in wolves.
In this post we would like to describe the video-documented attack of a brown bear on a wolf den. However, first of all we will tell some preliminary stories on the question in Naliboki Forest. In the second half of May 2019 in Naliboki Forest we registered very plausible killing of small wolf pups by a brown bear. Two brown bears (mating couple) frequently followed the wolf couple at denning, they inspected their dens, and finally the wolf litter disappeared (See another post).
Also, in May-June of 2018 in Naliboki Forest we registered similar behaviour of another adult male bear in relation to other wolf breeders, but that case was less documented.
Moreover, in July-September of 2018 in Naliboki Forest we documented regular visiting of homesite of another wolf family with relatively small pups 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.
However, still a direct attack of a brown bear on a wolf den was not photo- or video-documented.
Recently i.e. during May of 2021 one of the discovered wolf dens was situated in an enlarged red fox earth. Six pups of about 10-12 days old were in a burrow chamber of 1.5 meters deep. In a few days after this finding, being already convinced that the pups are normally nursed by their mother, we carefully set a camera-trap on a big pine at a distance of about 10 meters from the entrance of the burrow-den and the height of about 4 meters.
When we came there in two weeks, the den was destroyed by a brown bear. The video we could take from that distance (part of the event appeared out of the camera shooting) you can see below.
The brown bear discovered the wolf den and began destroying it. Extirpation of that by the bear took half an hour. It looks like the parent wolves were observing the bear’s action from aside, but they were afraid to approach the bear and attack it. Right after the bear has gone the parent wolves came to the extirpated den. They looked scared. After some shy and careful inspection of the den-site, the parent wolves left the place and came back there only at night. Also, they returned to the den-site few more nights, tried to dig and investigated the burrow-den inside and searched for their pups. Plausibly, the pups were killed and, perhaps, eaten by the bear.
During a week we (together with Gerard Oonk) traced the location and behavioural traits of the wolf couple with their tracks. Our preliminary, but very plausible inference is that the wolf couple lost the pups. The wolf couple began to range within almost the former winter home range, marked forest roads a lot and showed slow manner of walking on forest roads. All these traits did not match with usual behaviour for parent wolves. Conversely, they are rather opposite to the behavioural features of wolf parents having small pups.