As a former researcher of wild European mink populations, I should have published these findings two decades ago. But better late than never. Back then, my attention was consumed by large carnivores and their conservation challenges, and I regret having neglected other essential topics. That oversight still weighs on me.
Despite being fully engaged with wolves, lynxes, and bears, I now feel compelled to share this post on my zoological blog. My sense of responsibility is heightened by the fact that, to my knowledge, only my team and I in Belarus have studied a truly wild, local population of European mink within the broader vertebrate predator-prey community (see Sidorovich, 2011). This unique perspective allowed us to observe a critical threat that others may have missed: the pronounced menace posed by red foxes.
Therefore, without taking this impact into account, several reintroduction programs got stuck. A bigger problem arises from this – not just the failure of a particular project, but the impression each failure creates: that reintroducing the European mink into the wild and rescuing the species is simply not possible. On the other hand, I only recently came to fully understand the dramatic influence of red foxes on European mink populations in terrains where forested habitats cover only part of the landscape and where lynxes and wolves are uncommon. This impact became clear enough to me when I found out about the recurring dead ends in several long-term conservation programs for the European mink.
Also, at the end of this introduction, I would like to somewhat mitigate the fault I mentioned earlier, because the data I will refer to below were published in my scientific articles and books. So, they have been available for consideration by anyone concerned.
Fieldwork and Findings: What We Missed
Now to the topic itself. An intensive study on the population ecology of the European mink, a critically endangered species, was conducted in the Lovat terrain of the Paazierre Forest, northern Belarus, between 1988 and 2000. The most focused phase of research took place from 1995 to 1997, in collaboration with Prof. Dr. David Macdonald and Dr. Hans Kruuk. During that period, we radiotagged a total of 38 European mink, of which 18 individuals were tracked long enough to gather substantial data. Later, from 1998 to 2000, eleven more European mink were radiotagged and monitored less intensively, but each was tracked until its death.
Our focus was on the European mink’s role within the community of semi-aquatic mustelids inhabiting riparian zones –alongside the American mink, otter, and polecat. We also considered the influence of beaver activity on these habitats, which generally had a positive effect on riparian mustelid populations.
We documented aggressive encounters between American and European mink, displacement of breeding females into suboptimal forest habitats (mainly black alder swamps), and high cub mortality. These factors contributed to the rapid decline of local European mink populations.
However, during the study, we clearly missed one very important factor – one that, on a European scale, was no less significant than the impact of the American mink. I mean the killing pressure from red foxes. In general, the impact of red foxes was greatly underestimated. By not taking it into account, I mistakenly believed in the idea that, since European mink and red foxes had coexisted over evolutionary time, there would be no critically negative impact from red foxes on European mink in semi-natural terrain, at least.
But what could have been going on in rural terrains – I didn’t think about that. However, at that time, I should have taken into account the species’ demise in many regions of Western Europe even before the arrival of the American mink, and I should have searched for an answer to that question. But I didn’t. I quieted myself by saying that perhaps a complex of man-made factors had led to the vanishing of the European mink in those regions. Still, back then, I didn’t consider which of those factors might have been the main one in those cases.
Actually, on one hand, it was difficult for us to realize that red foxes could impact the European mink population so seriously. The red fox density in the semi-natural terrain of the Lovat upper reaches (NE Belarus), where we conducted our study, was only about 1.4 individuals per square kilometre –compared to 3-7 red foxes per square kilometre in other, more rural areas that were still quite forested (about 20-40%), where fox density was estimated.
It’s worth noting that we later became convinced that the red fox numbers in those more rural areas were likely underestimated. During winter, hunters in areas of about 10-30 square kilometres typically killed approximately 70-180 red foxes. Of course, many of those foxes could have entered the area from adjacent home ranges, but even so, this fact suggests that our earlier estimates of red fox density were plausibly too low.
On the other hand, even during our study of the European mink in the Lovat upper reaches (NE Belarus) in the 1990s, we faced a striking fact: out of the 49 European mink we radiotracked, 37 were eventually killed by predators (red fox, raccoon dog, polecat, lynx, wolf) – mainly by red foxes, with a total of 28 confirmed cases. These data should have prompted me to think more deeply about other aspects of the European mink’s demise elsewhere. But I didn’t. I became increasingly absorbed in the study of large carnivores and, after the European mink disappeared from Belarus, I lost the opportunity to continue that research – and gradually lost interest in dealing with this extinct species.
It’s important to note that captive-bred or captive-raised mink are even more vulnerable. In areas where red foxes are common, releasing European mink becomes little more than a fatal training ground for red foxes. It’s a grim reality, dear colleagues.
Let’s examine why the impact of red foxes has become so dramatic – and under what conditions it might be less severe. In my monograph on lynxes (Sidorovich, 2022), I presented long-term monitoring data from the Naliboki Forest that addresses this question.
In the Naliboki Forest, lynx, wolf, and red fox populations have been monitored since 2000 (see Sidorovich, 2020). Lynx numbers increased from 5-15 individuals across the entire forest in the early 2000s to 60-100 by 2016-2019. Between 1999 and 2014, the number of wolf packs varied between 6 and 14, with total wolf numbers ranging from 27 to 70. However, once lynx populations reached high densities, wolf numbers began fluctuating significantly throughout the year (Sidorovich and Rotenko, 2019).
Amid these changes in large carnivore populations, red fox numbers in winter dropped dramatically – by 10 to 20 times – between 2014 and 2017, compared to the first decade of the 2000s, when densities reached 50-70 individuals per 100 km² (see Sidorovich, 2016 for details). By 2017-2019, with 5-8 lynxes and wolves combined per 100 km² of forest, red foxes had become genuinely rare in midwinter – only one individual per 10-20 km² on average.
Only wolves and lynxes, when common in the habitat, are able to maintain a low density of red foxes. Let’s look at the data. Based on snow-tracking records of lynxes – covering approximately 1,800 km of track trails monitored between 1990 and 2008 – we calculated that a lynx killed one red fox every 16 days and one raccoon dog every 29 days. On average, a lynx killed 23 red foxes and 12 raccoon dogs per year.
In this snow-tracking study, only 23.7% of the killed red foxes (n = 38) and 43.3% of the killed raccoon dogs (n = 30) were at least partially eaten by lynxes. The rest were left uneaten.
Similarly, from snow-tracking data on wolves – covering about 2,200 km of track trails over the same period – we calculated that a wolf killed one red fox every 28 days and one raccoon dog every 19 days. On average, a wolf killed 13 red foxes and 19 raccoon dogs per year. Only 15.2% of the killed red foxes (n = 33) and 22.7% of the killed raccoon dogs (n = 66) were at least partially eaten by wolves.
So, wolves consume their carnivore kills less frequently than lynxes do.
However, in rural landscapes where forests cover only part of the terrain, red fox populations are so productive that even healthy lynx and wolf populations cannot suppress them effectively. In such areas, red fox densities may be 30 to 100 times higher than in fully forested regions with robust populations of large carnivores.
In these high-fox-density regions, reintroduction of European mink is doomed from the outset. Without consistent and effective red fox control – whether through natural predation or sustained hunting – such efforts become a tragic waste.
A Way Forward
To escape this reintroduction trap, three conditions must be met:
Absence or minimal presence of American mink. This has long been recognized as essential.
Low red fox density (≤0.3 individuals/km²). Sustainable only in large forest massifs where lynxes and wolves are common. Hunting alone is unreliable for long-term fox control.
Pre-release training in a large enclosure (8–12 hectares). The enclosure should include ponds and waterways, with up to 100 European minks kept and fed for at least a year. The habitat must be equipped with dense artificial refuges. A single pet red fox should live permanently in the enclosure, with food provided. It may kill 10–20 mink, but the survivors will learn to avoid foxes – dramatically improving their post-release survival.
Zoology by Vadim Sidorovich 
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