This year I have been following more closely the activities of several beaver families on our river as well as in the region (one of the families resides in an agricultural ditch system and another family lives in a small pond surrounded by agriculture – I believed they travelled there, as well, along the ditches during flood incidents).
The following observations have been made on an entirely subjective basis (overall impressions), not any true counts.
In summer, if I happened to see or hear adult beavers, they mostly appeared to forage separately – at a distance of about 500 metres or more from one another.
I could not always differentiate between parents of the kits of the year vs. yearlings and other older offspring.
Observations in one of the families seemed particularly striking mainly because I was aware of their den site.
It should be noted that on our river, beavers do not build lodges, nor dams.
They reside in underground burrows and they do not even create winter food piles (although I suspect they might carry some preserves into the burrows when it becomes colder because, during a very cold spell last winter, I observed such suspiciously low beaver activity that they would have starved unless they had stacked food somewhere unseen to me).
Returning to the particular family – their den burrow was located under a small growth of willows and that is where the kits emerged in the end of July and where the kits spent their time.
Meanwhile, one of the adult beavers usually foraged downstream from the den (ca. 300 – 500 m) and the other adult beaver, at the same time, foraged upstream from the den (ca. 200 – 400 m).
More rarely, one of the adults foraged downstream while the other foraged right across the river from the den (in a regrowing clearing).
This family lived on a river stretch where the foraging resources are distributed rather evenly (but not abundantly).
In other families, as well, I observed spatially segregated foraging behaviour by the adult beavers during summer but in these families I was not aware of the den sites (apart from 2 families but 1 of these I could not observe during summer due to restricted access and the other family I observed very infrequently to form conclusions about the typical foraging sites of the adults).
I rather decided that perhaps adult beavers are ‘loners’ and mostly forage on their own (like badgers do unless food resources are superabundant such as in artificial feeding sites).
However, during November, I have observed beavers in these same families hanging out closer together.
At least in three families I have seen the beavers or heard them slapping tails within 100 metres from one another.
I began wondering whether it is just coincidental or perhaps there is a pattern to this behaviour, namely, that the adult beavers forage separately during summer but the family rather comes together during late autumn/winter.
I should mention that it is not very cold yet (temperatures mainly keep above zero during day and have fallen to -1 degree Celsius at some nights over the past weeks) and I do not believe that this relatively mild winter weather constitutes the reason for change in behaviour (keeping closer to den, restricting movement).
There might be benefits to foraging separately during summer.
For example, as I was considering the particular family with the known natal den site, I thought that perhaps the parents split and one of them goes upstream while the other goes downstream whence they can keep track of possible threats to the kits that are located more or less in the middle.
Threats from land are very limited in our area (no large predators, few stray dogs) but kits would be nevertheless in danger from, for example, foxes.
The distributed foraging by parents might serve as a vigilance strategy regarding their kits that are thereby buffered from both sides.
Interestingly, one of the adult beavers often foraged close to where human trails descend from the uphill areas to the river while the other adult beaver foraged close to a riparian forest trail used by some fishermen and one local family.
If I had to make a decision where to watch out for approaching humans or dogs, that is where I would establish my post.
Wildlife, meanwhile, tends to travel on the other side of the river from the den (and the river is rather deep and wide where the den is located).
But I believe that any movement between the den and the foraging sites of the adults would be within a hearing distance of both adults.
There could be additional reasons.
For example, the nutritional needs by a lactating mother beaver might be different from those of her more mobile and less nutritionally stressed mate.
The mother beaver would also need to keep closer to the den in order to return and to nurse the kits (although some research has not found significant differences in the movement rates between the lactating female and her mate).
However, it is not truly about the movement itself.
It might be about the forage species or the age of vegetation growth or some other aspects that affect the nutritional value of the plants.
Additionally, if the mother and the father tend to bring some solid food back to the den for kits (and I did make most of my observations quite close to emergence from den when kits probably have begun taking solid food), it might be beneficial to provide a variety of food items.
The riparian vegetation is not so uniform here as it has been affected by land use and other factors.
Accordingly, if the mother and the father forage in different locations, the twigs or branches that they take back to the den might represent a greater variety of tree species possibly benefitting the offspring.
Other reasons might be at play which I have not yet thought of.
I wonder if beavers, indeed, have some strategy and if they do forage more distantly to one another during some periods while more closely during others.
Another family that I observed and that occupies the agricultural ditches did not forage closely to one another in November.
But they also seem intent to building something because they fall rather large birch trees (ca. 15 cm diameter at breast height) and they remove the trees from the site where they have been felled.
Mostly, such large trees are consumed on site and only twigs are dragged to the shore.
This suggests the family has construction plans on mind (their habitat is the least optimal and improvements might be necessary to retain water and to find shelter) and their separately managed activity might be caused by the patchy distribution of appropriate construction material.
Notes by Ieva 