Declines in mountain hares in Naliboki Forest, central west of Belarus: hypotheses and arguments

Before,  in 1950s-1970s the mountain hare was common species in Naliboki Forest. According to the local hunter’s words in those winters the species tracks covered snow cover densely and more or less evenly in each fragment of this forested terrain. In the late 1990s and beginning of 2000s it looked like  the mountain hare local population density in Naliboki Forest was evidently in a decline; there were censused only 0.2-0.8 inds per one square km.  In 2005-2010 the evident growth of the local population of mountain hare was registered, and more or less high number of the species continued till 2014 (2.9-6.1 inds per one square km). Then during the each next winter we faced with fewer and fewer number of mountain hares in Naliboki Forest.

In the period of 2005-2014 the local population of mountain hare in Naliboki Forest was one of the last dense local populations of the species in Belarus. In many other forest massifs in Belarus mountain hares were in a deep decline.  In 2006–2007 the special studies on the question of the decline in mountain hares in forest massifs in Belarus were carried out. The studies were fulfilled in Naliboki Forest, too, where mountain hares were relatively common at that time. This research project was not resulted in a clear answer. Meantime, we found strikingly different situations in hare populations in different areas; always low population density of the mountain hare was registered in the forested terrains, where the raccoon dog got relatively high population density (approximately higher than 50 inds/100 square km). High density in a local population of the raccoon dog in a given year messages that such a high density of this predator was in the terrain for several years already.Also, let us remark here that states of local populations of the raccoon dog (e.g. high or low density) may differ in different forested terrains (Sidorovich, 2011) that match with the revealed peculiarities in hare distribution which was found to be rich in contrast in Belarus. Usually the portion of hares in raccoon dog diet was not high (Sidorovich et al., 2008; Sidorovich, 2011); and this predator was hardly able to prey upon an adult healthy hare. Nevertheless, young hares may be successfully gathered by raccoon dogs taking into account raccoon dog’s foraging style of a scavenger and frequently high population density of this alien predator.

Here it is worthwhile to notice that in 2006-2007 in Naliboki Forest the population density of raccoon dogs was rather low.  In Naliboki Forest the decline in raccoon dogs happened in early 2000s, and still the number of raccoon dogs there is relatively low. That decline in raccoon dogs in the beginning of 2000s was plausibly caused by diseases (high infestation by trematodas Alaria alata, mange disease), but then a regular extermination   of raccoon dogs by wolves and lynxes in the conditions of the low number of raccoon dogs maintained the species sparse population.

In our point of view crash in the mountain hare local populations in many forest massifs in Belarus was also based on other situation observed. We noticed that usually the mountain hare population decline happened in the first year of recurrent population crash in Microtus voles. This specificity was connected with predation of the red fox and its population dynamics (Sidorovich, 2011). During one or two previous years with population outbreak in Microtus voles red foxes intensively reproduced. The next year with crash in Microtus vole populations numerous red foxes joined raccoon dogs in taking of young hares, and the hare populations began to decline. Concerning red fox predation upon hares, they were not a rare prey consumed by red foxes (Sidorovich, 2011). So, this is the hypothesis on the decline in hares, first of all, local populations of the mountain hare. Briefly, in a particular situation after the population crash in Microtus voles raccoon dogs together with red foxes exterminate the most of young hares, and mountain hare population declines.

With the respect to the above hypothesis, we assume that the registered decline in mountain hares in Naliboki Forest in the late 1990s and beginning of 2000s was connected with the documented high population density of raccoon dogs in the late 1990s. Then after raccoon dog got a low population density there, the mountain hare population recovered there. However, why did the mountain hare local population decline in Naliboki Forest since 2014 again? The case may be not predating of young hares by raccoon dogs and red foxes, because these two predator species were still not so common in Naliboki Forest due to their continuous extermination by wolves and particularly by lynxes that got the high population density since 2015 there.

We think that two following factors are responsible for that next decline in mountain hares in Naliboki Forest. First, the high number of lynxes (up to 6 ids per 100 square km) that try to  hunt mountain hares quite often. Second factor may be mild winters with little snow since 2014. In such little snow winter bigger brown hares began substituting for mountain hares. Before, when in Naliboki Forest there was a long winter with deep and loose snow cover, brown hares could not continuously inhabit forest habitats in forest massifs, because they are not adapted to move on a deep and loose snow. Nowadays with the global warming, bigger brown hares may be in a competitive advantage compared to mountain hares even in forest massifs.  In Naliboki Forest brown hares come in forest habitats from large openings that are so common there. Usually these large openings appeared as drained lands in 1960s-1980s. Brown hares were common in such habitats in Naliboki Forest continuously.