Last December (2023) I noticed mink tracks by the river.
It was an American mink. We do not have European mink in this region. I have also seen the mink occasionally during spring/summer.
At the time, it was cold, the ground was covered with about 10 cm snow (which was, however, crusty and the mink… did not sink in it).
The river was not frozen over entirely but there was significant ice cover by the banks with the middle section open.
The mink tracks came out of the water and across the bankside ice onto the shore which borders a very narrow strip (ca. 5 metres) of riparian tree grove.
The mink travelled through the grove and ended up on an open hayfield which is not very large although I am not equipped to estimate hectarage.
It is not even a hectare in size but perhaps 1/3 - 1/2 of a hectare.
The mink had begun crossing the field and then, not far from the tree line, it had made an ‘erratic’ move to the right only to return to the previous intended route.
I am not certain what caused the deviation.
There were no other tracks nearby and I do not believe that there was any actual interaction between the mink and some other animal.
Perhaps the mink had heard some noise (there is a wider forest band quite nearby, within about 10 – 15 m) and briefly thought to quickly return to the water through the tree grove.
As the mink apprehended it was no danger, it probably resumed its former course.
From then on, in a straight line the mink cut across the hayfield and climbed down the steep bank to the river.
Interestingly, there are a bunch of trees near where the mink descended and I believe last summer the beavers denned under those trees.
But I also observed mink near those burrows two or three times and perhaps the mink and the beavers share a riparian den under those trees (maybe at the same time but maybe not).
I believe I had observed the mink near the den when the beaver kits would have been too large to be preyed upon.
Overall, the mink tracks suggested to me that the mink had used a shortcut across the hayfield risking the more open habitat (and being more twitchy perhaps during this crossing) in order to reduce travelling time either in water, or along the riparian ice (or both).
I have recently read the book by Kruuk, H. ‘Otters: Ecology, Behaviour and Conservation’ (2006) where it was discussed how semi-aquatic mustelids struggle to thermoregulate in water and how swimming (especially, in cold water) can be enormously energy demanding for these species that are elongated (large surface area through which heat is lost) and that do not accumulate fat.
Eurasian otters, too, apparently take shortcuts across dry land (e.g., peninsulas) in order to stay out of water unless fishing.
One of the factors motivating the mink (and I suppose the behaviour could easily be extended to the European mink, as well, because the two species do not differ as greatly in this regard) would have been to reduce water exposure (under conditions where the air temperatures had been substantially below zero for about a month and ice cover was partly formed).
The river is meandering in the site and while it hardly forms a peninsula in that particular spot, the difference between the length of the river (between where the mink had emerged out of the water and where it ended up in the water again) and the shortcut route across open field would be perhaps 70 metres vs. 20 metres.
The mink did not necessarily have to swim.
The mink could have travelled along the ice boundary or on the shoreline which thereabouts forms a narrow (5 metres) open strip between the waterline and the riparian trees.
However, the path would have been longer and winding (the same 70 metres or so).
Thus, I also believe that the mink’s objective was not just to avoid water but also to reduce the time spent in travel.
The mink does not, nevertheless, appear to do so too often because most tracks are observed close to the shore.
Perhaps there was an additional factor prompting the mink to take the shortcut but as I do not even know at what time of day or night the mink travelled and the tracks did not provide much of other evidence of motif, I am unable to say why mink typically meander along the river but sometimes travel in straight line across dry land.
It could be related to the purpose of travelling.
If the mink is foraging, it might prefer staying close to the water/riparian tree habitat.
If the mink is done foraging and heads back to its resting site (and it is possible that the mink has a winter den right in the spot where it ended up), it might prefer straight line no-nonsense routes.
References
Kruuk, Hans, Otters: Ecology, behaviour and conservation Otters : Ecology Behaviour and Conservation. 2006. Oxford: Oxford University Press, ISBN 10: 0198565860 – ISBN 13: 9780198565864
Notes by Ieva 