Last Friday (Feb 9) I went to a site where I was not really expecting to encounter beavers because typically they concentrate their activities upstream during this period.
However, as I was walking along the shoreline, I heard the unmistakeable sound of beaver foraging on the other side of the river.
Here some layout of the spatial circumstance should be given.
On my side of the river, there is a hay meadow (perhaps 2/3 of a hectare) and the shoreline has very few trees and shrubs.
The line of trees and shrubs is almost unbroken but it is only 1 metre wide.
On the other side of the river, there is a slope which is overgrown densely with small deciduous trees (only around 5 cm in diameter at breast height).
The only larger trees are pines that are way upslope.
The slope is probably at approximately 30 – 40° angle relative to the water level and the bank is also eroded and almost vertical above the water.
At the time, it had been snowing generously.
The slope probably had less dense slow cover due to the presence of the thick grove of trees but on the hayfield side the snow was very challenging to tread (maybe 30 cm or more).
The central-place foraging theory states that beavers should prefer to cut down trees close to the river but sometimes they must take trees farther from the shore.
However, beavers should prefer to gnaw the tree off and then drag it down to the shore where it could be consumed safely near the water which provides shelter from sudden threats (e.g., predators).
This is what I have observed beavers do, as well, and frequently one finds the remains of their meals right by the water or washed slightly downstream and stuck in some obstacle to their passage.
Therefore, despite the freezing weather, I thought I would sit quietly and wait for the beaver to drag its meal down to the water where I would be able to observe the beaver.
The trees were not large and they could have been easily dragged down although perhaps some impediment would be caused by the very density of the grove (the stems of other trees might make it difficult for the beaver to navigate the cut tree down the slope; however, I do not suppose it would have daunted the beaver greatly for they seem very capable of manipulating their acquisitions through many types of vegetation and over many types of substrates).
The beaver was foraging rather high up the slope and there it was completely concealed by the vegetation.
I could not see it, I could only hear it.
The beaver had not noticed me, nor it actually noticed me at any point and thereby its behaviour was not influenced by my presence.
I waited and I waited.
Granted that the beaver had started cutting the tree(s) before I arrived, altogether about 7 – 10 minutes elapsed before I had gotten so terribly cold that I had to leave the exposed and damp habitat.
I thought it was curious that the beaver never appeared by the river, especially, because there were no large trees that would demand a prolonged effort.
The pines are very rarely touched by beavers and the couple of pines were growing at the very top of the slope.
Judging by the sound, the beaver was located somewhere in the dense grove, in the middle section of the grove.
The following day (Saturday, Feb 10) I returned and I heard the beaver foraging in about the same area (precisely the same conditions, only slightly to the right).
Once more, I waited for about 10 minutes and the beaver did not emerge out of the grove to attest to its central-place foraging habit.
I have watched a beaver kit take down a sapling (a 50 cm tall tree) within 2 seconds.
Hardly the beaver would need > 10 minutes to cut down any of the trees in that grove.
I began wondering why the beaver had changed its typical modus operandi.
I realized that there might be three factors involved which were probably correlated.
Firstly (but less importantly), the eroded bank did not offer cosy and snug patches where the beaver could locate itself in order to finish off the tree.
For most part along that shore, the slope abruptly ended with a vertical bank that reached down to the water without any sandy or muddy or even ice-covered edge between the water and the bank.
However, the beaver might have wished to at least stay on the lower parts of the slope to be closer to the water in case of emergency if not right beside or in the water.
Another factor which was probably the decisive one was the steepness of the slope in combination with the recently thick snow cover.
It was a slope that would cause a non-athlete human hear their own heart beating and become short of breath.
There are not many natural enemies for adult beavers in this area (apart from humans and dogs) and I believe that the beaver had made a trade-off between the safety of the shore and the energy spent in the effort to climb up the shore, cut the tree, climb down to consume it and climb up again.
It must have been more energy-efficient for the beaver to stay middle-slope right where it had cut down the tree and finish the tree right there rather than investing strength in the steep travel which would include the transportation of the cut items.
However, it should be noted that the beaver was (at least from my side of the river) completely concealed by the trees and perhaps the beaver had taken this into account, as well, by exchanging the aquatic haven for a temporary shield of the dense growth.
Thus, I believe that beavers might not at all times stick to their central-place foraging strategy by taking every tree it cuts down to the shore to consume it safely.
When faced with conditions where the travel to the selected trees is energy-demanding (snowy upslope) and the riparian area does not offer suitable feeding platforms, either, the beaver might decide to have its meal in the place where it was acquired without first transporting it to a safer location.
The beaver might compensate the distance from water (which in this case, measured as a line along the slope, could have been perhaps 15 metres) by choosing to cut and consume trees in a spot where the sheer density of the grove would conceal the beaver from unwanted spectators.
The microclimate of the grove would have also been favourable during the first morning (Feb 9) when windchill was significant.
The beaver had options of foraging in slightly more open areas on that slope where it would have stuck out against the snow but it did not because I never saw it.
Interestingly, on Feb 9, I briefly observed another adult beaver swimming in the water near the section where its buddy (mate?) was foraging upslope.
I wonder if this other beaver appreciated that its fellow had chosen a more dangerous foraging site and invested some effort in patrolling on behalf of its associate.
The second beaver never got out on the shore but it swam along the section several times.
I do not suppose it noticed me.
Perhaps it was safeguarding its mate (?) from the water, ready to warn it timely against threats.
The second beaver was not observed on Feb 10 but I only stayed for about 10 minutes.
Notes by Ieva 