Till the 1960s Naliboki Forest, which is situated in the north-western Belarus, was a greatly swamped terrain, where on the area about two thousands km2 swamps of various types and sizes were interspersed with dry land forests the terrain-wide. Open grassy marshes constituted about 19% of the terrain. Approximately a third part of the forest habitats that covered about 76% of the area were swamped too (Sidorovich, 2016). Such a swamped forest was either in kinds of black alder and downy birch mixture (with prevalence of one of the species) or that was raised bogs with suppressed or normal pines.During draining during 1960s-1980s something between 3 and 4 thousands kilometers of drainage canals appeared in Naliboki Forest – on average about 1.78 km per one km2 of the terrain (Sidorovich, 2016). In effect the density of watercourse network (canals and rivers altogether) increased 2.6 times, and it became 2.1 km per km2versus 0.8 km per km2 before the draining. The drainage canals gradually overgrew with willow bushes and young trees and they became relevant, even favourable habitats for beavers.
Beavers became to inhabit the variety of drainage canals in Naliboki Forest and finally all these new habitats were populated by the species. In the late 2000s and early 2010s beavers by densely occupying both rivers and numerous drainage canals inhabited Naliboki Forest with the population density of 1 to 8 settlements per 1 km2 or on the average 3-4 settlements per 1 km2 . At that time usually there was one beaver settlement per 0.8-1.2 km of river stretch and one beaver settlement per 0.5-2 km of drainage canals. In the late 2000s and early 2010s in the whole Naliboki Forest on the area of about 1.71 thousands there were about 5-7 thousand beaver settlements, where 20-40 thousand beavers lived. On small watercourses (small rivers and drainage canals) each beaver settlement has approximately from one to 4 ponds and in the majority of the cases there were 2 or 3 ponds. So, in the late 2000s and early 2010s in the whole Naliboki Forest there were about 4 thousands beaver ponds, which were full of water. Additionally, there were 2-3 thousand pond remains from the abandoned settlements of beavers.
By considering the cases of drought in Naliboki Forest in 1994-2013 (Sidorovich, 2016), there was not found any regularity nor trend at a multiannual scale in the distribution of drought periods. It may be only noted that summer drought in Naliboki Forest became happening slightly more often.
Later in 2014-2018 it was becoming more and more evident that summers in Naliboki Forest were indeed getting of markedly hotter and drier. The weather situation in Naliboki Forest in 2014–2015 as well as during summer of 2018 suggests that. In 2014-2015 after the fairly dry second half of warm season in 2014 and after the winter of 2014–2015 with little snow, July-September of 2015 were relatively hot and very dry. By observing the hydrological situation in Naliboki Forest since 1982, I have never seen so low water-table and so much drying up of streams, particularly, drainage canals and their beaver ponds. The same disaster on drainage canals and small rivers repeated during the hot and dry summer of 2018.
In such conditions beavers appeared without enough, even minimum water environment that is a crucial factors of their safety from attacks of their predators, first of all, wolves and brown bears. When all the watercourses are populated by beavers, any relocating outside of their settlements are risky due to pronounced intraspecific interference between beavers. Being without safe water environment beavers tried to persist in their extensive burrow network and in big lodges with some burrows around. Anyway, wolves and also brown bears and lynxes killed them frequently in this situation as well as red foxes killed young beavers.
During summers 2015 and 2018 by applying camera-traps we traced 7 beaver settlements, which ponds dried up. The results were following. Across such unfavourable conditions only 5 out of 9 beavers , 1 out of 3, 2 out of 4, 1 out of 4, 1 out of 5, 3 out of 7, and 0 out of 2 beavers had survived. That means only 38% beavers, which faced with their ponds had dried up, have survived. In effect, nowadays in Naliboki Forest there are approximately only a half of beavers and about 60-70% of the species settlements compared the beaver population in the late 2000s and early 2010s there.
Concerning predation on beavers in Naliboki Forest, it may be added the following. In the monograph about Naliboki Forest (Sidorovich, 2016) there was shown that feeding of wolves, particularly diets of wolf pups relied beavers a lot. During the summers of 2015 and 2018 wolf predation on beavers happened even considerably more often. By avoiding a precise data with the comprehensive scientific form of their presentation, I will state that, at least, in 2 out of 3 wolf scats there were much hair of beavers, and one of these two scats contained merely beaver remains. So, let’s say that in Naliboki Forest during the summers of 2015 and 2018 the beaver portion in the biomass consumed by wolves was not lower than 60%.
As to brown bears, everyone of seven individuals, which were investigated, caught beavers too. Two brown bears almost specialized in feeding on beavers in the period from early July till mid-October. Approximate portion of beavers in the diets of the seven bears varied from 10 to 80% of biomass consumed (again I avoid the obtained precise data in such a form of presentation of the results).
Moreover, during the last summer some of lynxes (at least, four adult males and one mother with two kittens) in Naliboki Forest hunted beavers quite often (about 30-50% of their diets in July-October).
Finally, I would like to present many photos that are well illustrate the situation above-described.
Zoology by Vadim Sidorovich 