Tonight I was further contemplating the creative non-traditionalist beaver family I dedicated a post to yesterday (Beaver observation (Apr 18, 2024) – do beavers take time to exercise?).
I realized that there was another spot where these individuals are often met and which is of low apparent use to them because it lacks in riparian vegetation (although the beavers forage inland some 30 – 50 metres upstream).
I am fairly certain it has not been a den site (burrow), either, at least not up until this year.
As we were walking by, I saw a beaver which was swimming in this spot and the beaver disappeared amidst some tangled half-submerged large boughs of a fallen tree which constituted a part of a log jam.
Previously, there had also been a log jam but it was minor and mostly composed of one smaller log and plenty of clogged trash.
However, there had been a tree which used to hang over the river.
It had been uprooted by wind but due to the erosion of the banks, it had never fully hit the water and its trunk had been situated way above water level (at least 1 metre) with only some branches in the stream.
Apparently, the spring flood combined with some windstorm events had succeeded in somehow forcing that large tree (oak?) down into the water.
Currently, the log jam has taken a peculiar shape forming a sort of a ‘cove’.
Namely, parts of the large tree are stuck upstream and any incoming debris (of natural or artificial origin) is caught into its boughs.
Meanwhile, the ‘old jam’ which was comprised of the smaller tree and some accumulated materials lies a bit downstream – not far, only about 3 – 4 metres from the upstream jam.
Between those two jams, a small ‘cove’ is formed where water seems to be rather deep.
There must be some boughs entangled below the water but, from this shore (the jams are located closer to the other shore with a gap of about 2 – 3 metres between this shore and the jams – a gap where water flows rather freely although the trunk of the large tree must be there below the water), it seemed that there was plenty of space to swim about.
I believe that beavers are using this structure as a safe haven because the tangled boughs (that form sort of a roof over the ‘cove’) would deter anyone who wished to enter and the only access was from water but water is quite deep thereabouts.
I tried to discern whether beavers have made some improvements to this structure (they might be hanging out there because they are thinking of converting the natural formation into a dam across the river) but it was too dark to really understand what was due to water flow’s impact and what could have been modified by the beavers.
It would be quite exciting if the beavers dammed the place up because they do not construct dams (nor lodges) on this river (there has been no need although over past summers the proportion of overly shallow water has increased considerably).
I have only seen two small dams (ca 1 m in width) in our whole area and both have been built to prevent water in ditches from flushing out into a river / a larger ditch system.
I also wonder whether the beavers are thinking of using the site as a natal den (granted that parturition date is approaching).
It is not a secluded site on a larger scale (pedestrian traffic, dogs walking, cows grazing) but, on a smaller scale (the immediate vicinity of the potential burrow), it is very well protected because nobody apart from mink can pass by those tangled branches both above and below water.
The jam is not even suited for trotting across because it does not extend from one shore to another and the above water parts form almost a maze while the straight trunk (which must have been severed from the base and sunken) is below water.
Perhaps beavers already have made a burrow there (not for natal den purposes but for a resting site near their frequented foraging patch).
I cannot say that beavers always prefer secluded sites for their natal dens.
The two dens that I was fortunate to observe last summer were only partly secluded and it seemed to me that the choice had been made based on the substrate availability for digging as well as the availability of a deep water ‘front yard’ (so that the kits emerging from the den could swim in deeper water where they were more secure).
It appeared that beavers had taken safety into account but it was mostly safety from the perspective of others gaining access to the den (not from the perspective of others being able to access the vaster neighbourhood of the den site).
For example, one of the dens was located on the opposite shore of the river (where people never walk but they can get there by wading across which is entirely possible) but there was a steep bank nearby which probably denied access for mammals such as foxes.
Foxes could climb down there but why would they?
I suppose that it would be insensible to construct a natal den, e.g., nearby a spot where many animals, including predators can easily access the river to drink or to cross it.
In this spot, nobody would have been greatly willing to approach the river.
The other den was, similarly, perhaps not even in the most greatly sequestered area on the beaver family’s range and it was constructed on the shore were humans sometimes show up (while the other shore is inhabited).
However, the bank was also extremely steep (almost vertical) with some trees providing their roots for stability (and it is important to note that beavers never touched these trees for foraging purposes), there was deep water 100 metres to both sides and the river was inaccessible from this shore for drinking or crossing purposes.
Thus, it might be that the inaccessibility of the log jam is a strong factor that the beavers are considering on a microscale (while pitting this factor against the daytime disturbance factors and the ephemeral nature of this structure which, unless fortified by the beavers, might only hold until the next strong flood which might follow only after the summer).
Perhaps they are hanging out nearby to test the site’s properties which is a curious notion because it would suggest that beavers are trying to imagine the site’s suitability from the viewpoint of their not-yet-born kits and living there temporarily to see whether the site was too loud during the day and otherwise perilous during night.
It might also imply that beavers are generally testing out the accessible burrows and new burrow sites prior to parturition in order to decide which was the best fitted for the purpose that year (dynamic decision making according to changing circumstances).
I would be ecstatic if they chose this site for giving birth to their kits because it is very easily observed from the trail.
Notes by Ieva 