There are several beaver (European beaver, Castor fiber) colonies (families) on the river that runs through my town.
The river is largely occupied at all segments.
However, the beavers do not really build dams, lodges and canals here and they rather make use of riparian burrows.
The river is not very big – in most places it is about 5 – 10 metres wide and rarely exceeds depth of 1 metre.
From what I gather, 1 m is the depth that is rather optimal for beavers.
During summer, however, this depth is hardly reached in most parts of the river and often the stream runs shallow (< 50 cm) for metres and even tens of metres through intensely used beaver habitat.
I am not sure if I have identified beaver burrows correctly (because I do not approach too close in order not to disturb them) but sometimes I believe that during decreased water level periods their entrance is above water level which is sort of considered a big ‘no no’ in beaver construction manuals 🙂
There are sufficient tree resources to construct dams, and the river is not too wide to accomplish this but the beavers just do not seem to be bothered (and this situation has lasted for decades).
This made me wonder regarding the reasons why our local beavers apply such ‘little effort’ to conceal their dens and to provide shelter for their daily commotion (especially in summer).
I was wondering if this could be related to the relatively low predation pressure in the area.
We do not have wolves in our (small) town, and the town is surrounded by vast agricultural lands that do not support wolf migration.
While there are wolves further away from the town (> 30 km), I do not believe that these town beavers have ever met a wolf in their life unless they dispersed from a wolf area.
We also do not have feral dogs, and stray dogs are only an occasional and short-lived occurrence in most places (some dogs wander during heat and then they get caught and delivered back home within a week).
I have never heard of dogs attacking beavers in this area.
The only mesopredator that lives in the town is the red fox (which is, however, abundant).
While red fox hardly poses threat to adult beavers, it might prey on beaver kits (? verification needed).
There is also the mink which might perhaps take newborn beaver babies.
Badgers (which I believe is a less water-tolerant species) live sporadically on beaver range.
Therefore, I was wondering if in such places where predation risk was relatively low, beavers tended to make ‘looser’ decisions regarding their engineering activities and whether they tended to just settle for riparian burrows not overworking themselves to conceal their dens and their activities.
This also made me wonder if there could be a pattern throughout the distribution range of the species where beavers constructed ponds, dams and canals more actively in places with higher predation pressure compared to places with lower predation pressure.
Perhaps beavers also construct a greater number of dams / lodges / canals where the predator pressure is higher (i.e., if the beavers build at all – the rates of construction might be increased in predator-inhabitated sites).
I have not found a publication which discusses this aspect of beaver activity, but I think it might be of relevance to address the possibility because beaver dams are so essential in river health and habitat restoration/creation.
If beavers are likelier to perform ecosystem engineering activities in places where they coexist with a substantial predator guild, this might point at the significance of the medium and large predator assemblies regarding the subsequent ecosystem services delivered by the beavers.
There has been much discussion regarding the key species that should be reintroduced in order to achieve, for example, our climate goals (e.g., ‘Rewilding the American West’, Ripple, W.J. et al., 2022).
If beaver dam-building activity was enhanced by mesopredator and apex predator presence, this might also mean that beaver-wolf reintroduction combined could provide greater benefits than reintroducing beavers alone.
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Later I also considered the human disturbance factor on the beaver building activities.
I had not thought of it initially because my town is very small and it is hardly even semi-urban but rather peri-urban in its character.
However, there has been a history of beaver persecution as well as misleading information on how beaver damming activities were detrimental to fish stocks or other human interest.
The region has up to now not been highly environmentally concerned either and many riparian habitats have been destroyed to pursue urbanization, agriculture, forestry or other purposes.
This could have caused instances of frequent (intentional or coincidental) destruction of beaver-engineered structures.
I began wondering that perhaps this has altered the beaver behaviour, as well.
Namely, where the beavers have settled in regions of high anthropogenic disturbance and where they at all (due to the physiological and hydrological regime of the river) live in underground burrows, they might rather select staying inconspicuous – not investing in building structures that could become destroyed by humans or that could direct humans to their kits.
This could be a factor in and near towns and cities where human behaviour might limit beaver construction aspirations despite these sites being suitable for beaver construction activities (sufficient resources, adequate stream and bank conditions).
In our region, many places might also not be highly suitable because the stream has eroded and the banks have become disproportionately high.
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There could be a whole gradient of beaver decisions regarding where and when to build and where and when not to build factoring in both predation and potential human disturbance (intentional destruction of beaver-made structures).
This could bear relevance to beaver ecosystem services.
References
William J Ripple, Christopher Wolf, Michael K Phillips, Robert L Beschta, John A Vucetich, J Boone Kauffman, Beverly E Law, Aaron J Wirsing, Joanna E Lambert, Elaine Leslie, Carly Vynne, Eric Dinerstein, Reed Noss, George Wuerthner, Dominick A DellaSala, Jeremy T Bruskotter, Michael Paul Nelson, Eileen Crist, Chris Darimont, Daniel M Ashe, Rewilding the American West, BioScience, Volume 72, Issue 10, October 2022, Pages 931–935, https://doi.org/10.1093/biosci/biac069
Notes by Ieva 