The summer of 2023 and also early autumn witnessed a couple of severe storms that uprooted or broke many trees.
I have been observing how these trees (that feel in the riparian area or close to it) have been utilized by beavers.
Some of my observations have already been summarized in Exploitation of windthrown trees by beavers with respect to season and climate but today I wished to add another post because I have been considering these events in my mind and I believe I have come to a conclusion that windthrows and windsnaps that occur in summer might be left relatively untouched by beavers until autumn/winter because beavers use these trees as another type of pantry (similar to food piles).
While food piles might be predominantly intended for feeding beaver kits (that can suffer more greatly from the cold winter weather), I think that adult beavers in many regions (with fluctuating winter weather) are aware that they will have opportunities to forage on the shore.
At the same time, these foraging trips might be cut short and infrequent and there is always a need to reduce exposure to cold (and predation).
As a consequence, adult beavers might leave windthrown trees relatively untouched if these trees have fallen during the season when beavers do not have much trouble obtaining forage on their own (spring, summer).
After the intense summer storm, I was very surprised to see how little beavers utilized the trees that had landed even very close to river.
I am not claiming that beavers did not use them at all.
But the proportion that they utilized was very small.
Initially, I wondered if beavers have some aversion for these type of ‘blessings’ (because they are, after all, a half-free meal), e.g., because they prefer to focus on younger saplings/suckers during the vegetation growth period or because the trees that had fallen were mostly ‘the wrong species’.
However, I began noticing heavy use of these windthrows (the ones that had not been removed by humans) in autumn/winter when the weather got cold (about -5 °C)).
The use became so intense that beavers even travelled rather long distances over land or along ditch systems to debark these trees.
This made me reconsider my ‘aversion hypothesis’ and I began thinking that perhaps beavers were storing the summertime windthrows ‘for laters’ (autumn/winter) when time to forage would be reduced (or it would be necessary to reduce it for body heat saving purposes).
If beavers had memorized the approximate locations of these resources, it might be beneficial during winter not to roam widely inspecting the riparian area for available forage but to march directly for these known forage sites (time and energy saving strategy).
Accordingly, food piles might serve as pantries mainly for kits (close to home, highly palatable resources) while fallen trees might be pantries for adults who can afford winter trips but who would prefer making them short and to the point.
I even began wondering if beavers might fell trees with the purpose of having these resources (bark) accessible during winter in known locations.
My reason for wondering was the observation of some beaver colonies that had more abundant riparian forest resources available to them, felling some trees in autumn without actually using them.
First of all, beavers here do not prepare food piles or do it very rarely, and the felled trees in autumn were not used for the purposes of stacking food (nor building/fixing dams and lodges because beavers on this river do not do that, either).
Also, some of these trees fell toward the forest interior and not toward the river.
Their canopies were rather far from the waterline.
Perhaps the beavers miscalculated or there was some other factor (e.g., strong, unexpected wind) that interfered with the intended direction.
However, I wonder if, alternatively, beavers might have deliberately fallen these trees in order to later access their trunks with the purpose of obtaining bark during winter.
These trees had some common characteristics, namely, they were very tall and branchless almost up to the very top, and they actually had more trunk-bark area than they had canopy.
Perhaps these trees were not felled ‘as a mistake’ but they had been selected for their bark area rather than their canopy.
Of course, there is a slight risk involved.
Humans tend to remove large woody debris and it can also be floated away during autumn floods.
Floods (and ice) actually improved accessibility of some windthrows further from the shore but, at the same time, also trees fallen very close to the river (before the floods) were not consumed until late autumn.
For example, my observations of greatly increased windthrow consumption in late autumn/early winter concern a relatively remote river sector where humans interfere minimally with the fallen trees.
There might also be preferential consumption of different parts of the windthrow, e.g., foraging twigs and branches while fresh and leaving bark for later periods of scarcity.
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Later on I also began wondering if there could be a seasonal difference in nutrient preferences.
If beavers predominantly aim for phloem which essentially transports leaf-produced carbohydrates, phloem might offer sugars for fattening up during autumn/winter period.
Notes by Ieva 