As I have been visiting (observing) our local beaver colonies (I prefer calling them families), I have noticed a certain tendency for the beavers to shift their predominant foraging locations (not on patch but on perhaps 100 – 200 m river channel segment) every week or so.
I should note that I am referring to observations outside of kit-raising (denning) period when beavers are probably restricted to the den site proximity (although not necessarily as there is no consensus that the female significantly reduces her travel rate during nursing compared to the male but it might depend on the territory size, forage availability in different patches etc.).
I am also excluding observations where, I believe, beavers have been exploring new foraging sites due to loss of habitat and/or due to, for example, flood that enables travel along ditches or that provide water shelter in the form of temporary pools/ponds in the riparian forest.
Overall, it appears to me that one week I meet beavers in more or less the same locations night by night until it becomes entirely predictable they would be found there.
And the following week, I walk down to meet the beavers in ‘the usual spot’ only to discover that they are not there and that they do not return during the days to come.
Instead, they can be found somewhere slightly downstream or upstream.
Unfortunately, I cannot access all the segments of the beaver territories on the river and therefore it is at the moment difficult for me to determine whether these shifts in foraging locations are periodic or they are also regular with respect to some type of rotational use of foraging patches (e.g., location 1 is always followed by location 2 which is always followed by location 3 which is then followed by location 1 and the cycle resumes perhaps sometimes skipping a location #? if there are more than 3 locations in the sequence).
After the shift, for about a week, it is, once again, rather predictable where the beavers would be encountered (in the new segment).
As I have been making observations for less than a year, it is also a bit preposterous to claim that these shifts are periodic and not seasonal.
However, I do not believe they are seasonal because I do not observe great differences between the subsequent locations where I have observed the beavers foraging week by week.
If the pattern was seasonal, there should be some habitat differences.
Also, seasonal differences would not manifest themselves on week by week basis.
On the other hand, the weather fluctuations have been great lately and these patterns should be observed in ‘steadier’ years weather-wise (if such years are still to occur).
Nevertheless, as I mentioned before, there are not any remarkable habitat differences where some type of resources would become available or unavailable and, frequently, the change in locations is not dramatic (e.g., the beaver has only travelled perhaps 200 – 400 m along the channel).
But there tends to be a slight shift in habitat type which does not translate into significant changes in resource composition but which is perceptible with respect to overall tree cover, slope etc.
Intuitively, I do not perceive that these differences are important from forage or weather protection etc. perspective but rather that, in the eyes of the beaver, they might assist in delineating sectors within its territory.
If the periodic shifts in foraging are observed by the beavers with the purpose to avoid depleting resources in one spot and to allow regeneration, then I would assume the change in ‘scenery’ might suggest to the beaver that it has moved out of one sector and into another.
It could be compared to the beavers having several dining rooms and trying to dine every week or so in another room.
In order to tell the rooms apart, they would use hints such as decoration (habitat type that results in a certain scenery and vegetation composition).
Perhaps the association between ‘a specific dining room interior’ and the period of time spent in it creates an internal response (‘I should be moving on to the next room’).
The association would not be formed if the rooms all looked the same and if it was not clear at all the beavers had moved from one room into another.
Thusly, it might be more difficult to make the judgment when to leave the current room (because there would be no sense of ‘accumulating presence’ with respect to the flow of time although one could argue beavers might not be using the cue of time but rather other cues such as accumulation of their own scent in a patch).
I have used the scale of ‘a week’ simply because it is how I can more easily distinguish between patterns (what happened last week seems different than what is happening this week as opposed to more natural – but, for a human, perhaps, more arbitrary – cycles of 10 days or 20 days etc.).
However, ‘weeks’ are probably not how beavers perceive their schedules (although they could be because most species adapt to human disturbance and our disturbance depends on whether it is a weekday or weekend; as a result, wildlife might have gotten the sense of ‘a week’, as well).
If I had to determine whether these periods are closer to 5 or 10 days, I would say – closer to 10 days.
These could be several reasons behind such behavioural pattern:
1
Beavers might be avoiding depleting their resources in any given spot and/or overbrowsing in any given area overly.
Some types of vegetation might also regrow during ca. 10 days or they might sufficiently elongate their parts of aboveground biomass by the time beavers return.
2
While the forage might be similar between some of these locations, the chemical (and thereby nutritional) content might differ.
Even the same species might accumulate different concentrations of nutrients based on habitat type.
The diversification of the diet, in species that forage in a mosaic of habitats, might not be based merely on consuming different plant species but also on consuming the same plant species that grow in different habitats.
For example, proximity to agricultural fields might raise the nitrogen level in plants due to eutrophication.
Meanwhile, the fertile riparian forest soils might provide micronutrients.
Thus, ensuring that the foraging occurs in different types of habitats within the mosaic, could promote the beaver’s fitness regardless of the heterogeneity or homogeneity of forage between these locations.
3
There could be some territorial defense considerations.
Beavers patrol their territory boundaries daily and therefore it is improbable that a lone beaver or a neighbour would assume that a portion of territory is no longer in use if it still falls between the defended and scent-marked boundaries but if it has fallen out of active use for a while.
On the other hand, if a beaver family predominantly foraged in a sector close to one boundary only paying occasional visits to mark the territory (but not staying there for hours or days), lone beavers or neighbours might sneak in to make use of the resources and when the beavers return after a long absence, they might discover the patch depleted rather than rejuvenated.
Abandoning a foraging spot for a long time (e.g., > 10 – 20 days) might put the resources in peril.
***
There could be other reasons behind such strategy.
I only wished to remark that despite the periodical moving around by the adults, I have often observed the beaver kits localizing near where I believe the den sites are (not necessarily natal den).
The kits appear to remain closer to the den than adults and not only during the summer when they are growing up but also during autumn and winter/early spring.
Winters used to be cold and limiting, and beaver kits are the age group most imperiled by cold winter weather.
Therefore, I suspect that during their entire first year, beaver kits stay close to the natal den but later to the wintering dens (or lodges in other areas) due to lower mobility and safety reasons early on and due to climate considerations in winter.
The fact that the kit behaviour does not change as greatly until perhaps their younger siblings are born and also because beavers seem to store food caches mainly for the use of the kits, I would say that beaver kits are thought of as ‘the babies of the family’ until they are ca., 12 months old and during this period their behaviour does not yet resemble the behaviour of adults closely.
However, I have noticed that beaver kits tremendously enjoy when their parent is foraging near the den (near them), and, on such occasions, I have observed exuberant behaviour that results in very low foraging activity and much ebullience which also suggest to me that the beaver kits might be feeling a bit lonely while waiting back at the vicinity of the den and that the periods during which the adults forage nearby, are welcomed by the kits with joy and affection.
Thus, it is possible that the onset of the next stage in maturity (yearling, juvenile) is not met with a sense of abandonment (‘mommy is taking care of the new babies now’) but rather gives rise to pride and even emotional/physical liberation as well as social inclusion as the kit can join the adults more freely in their foraging ventures up and down the stream.
This could ensure a very smooth and natural passing from kithood into yearling phase where any sense of loss is compensated by empowerment, freedom and a chance to actually spend more time with the parents.
Notes by Ieva 