This morning I visited a beaver family which I get to observe comparatively rarely because their territory is difficult to access.
Part of it (one side of the river) is private property and the other part (the other side of the river) can only be accessed by making a very long walk around because there is no bridge nearby.
I was quite surprised to learn that there were three adult beavers in this family.
Namely, the three beavers that I saw were grown-ups and approximately of the same size.
I have to assume that, in this family, an older offspring has stayed who is currently at least 2 years old (turning 3 this year).
It is in itself not extraordinary.
Dispersal age varies in beaver populations and it is even affected by density conditions.
In fact, one would expect older offspring remaining more often in our high density population.
There have not been any official estimates (that I know of) but, overall, there is not a section in the river which is not occupied, the territories have become smaller than they used to be years ago and some beavers have colonized agricultural ditches and ponds (suboptimal habitats that would not be colonized in a population of sparser density).
However, most families that I have observed consist of the parent pair + kits of the year + subadults who apparently tend to leave while they are yearlings.
This observation might be attributed to the decreasing quality of the riparian habitat.
The clearing of riparian trees and shrubs has become a norm rather than an exception, and the level of disturbance along the river has also grown.
I suppose that while it might benefit for the subordinates to stay longer in their families (in order to gain in size and in experience which could improve their chances at survival and establishment of their own families and territories once they eventually dispersed), it is not possible due to limited food resources.
Accordingly, I had not yet observed a family where the subordinate reached the size of their parents.
This family inhabits a river segment which is perhaps slightly (but not overly) better than most beaver homes.
There is disturbance on one side of the river but the other side has a relatively lush growth of shrubs and there are small fragments of riparian forest in some places.
This family might be better able to afford keeping older offspring around but barely so.
I am not yet certain whether the family also has yearlings (the almost two-year-olds now) and how many kits were born last year.
The reason for a two-year-old to have stayed longer in their natal territory could also be related to the family structure and the number of other siblings alive.
For example, if any yearling(s) had dispersed early (or died), the older sibling might not have to compete with them for the resources and would be allowed to linger on.
Regardless of incomplete data, I began wondering whether there could be any other motivations for the parents to retain the older-aged subordinate.
As I have mentioned before, their resources are not superabundant and if there were also kits and yearlings (which I have no reason to assume there were not), they would struggle to make their ends meet.
While this family has several ‘semi-pristine’ areas on its range, their home also includes a section that belongs to some private property owners and these people are extremely obnoxious.
They have acquired this riverside property to go there during summertime (at night) and to throw loud drinking parties (which is very disrespectful because it is, coincidentally, an area where other people go to rest from the town life quietly).
I suppose that the worst effect arises from their detestable taste in music.
They play music that resembles the beats one would expect to hear in a nightclub, and the music is played at full volume (the sound carries very well over the water, too).
I have previously made some observations that have led me to assume beavers do not tolerate loud noise and, especially, noise that produces vibrations.
I think that while the particular beaver family does not suffer constant disturbance, the sudden effects might be even worse (because the beavers cannot grow accustomed to them as they would in the case of daily background noise) and the disturbance also befalls them during the most vulnerable time (when kits are already born and when they are small).
If the noises are traumatic to the little ones, the beaver family might be in need of a babysitter who can stay near or in the den during these nights while the rest of the family forages, patrols the territory and pursues other beaver chores.
It is possible that they are taking shifts but it is also possible that the female cannot forego foraging as she needs to maintain her body condition in order to be able to nurse the kits.
Later, as the kits mature and forage is brought to them in the den, two adults might also be needed to efficiently provide for the little ones throughout the night.
Thusly, a babysitter is in demand so that the kits were not left alone during the disturbance, and such babysitter should be themselves:
- old enough not to be afraid;
- old enough to manage foraging quickly when they have the chance.
Perhaps age is of importance in other respects.
For example, if beavers were most affected by vibrations (as I suspect), larger beavers might be less affected due to their body size and shape.
They might remain calmer and they might retain their ability to forage efficiently despite the vibrations travelling through water.
Importantly, they might also remain capable of listening out for predators or any alarm sounds by the kits themselves.
Perhaps the sense of security is achieved through additional age-related traits.
For example, the beaver kits (who become exposed to this dreadful experience despite having perhaps never even left the den previously and having no knowledge of what the world outside is like; as a result, it might seem to the them that the world, whatever it may be like, is ending) might feel calmer if they can smell certain hormones or secretions produced by their babysitter.
If hormone/secretion production is age-dependent and yearlings either do not produce some hormones/secretions or the intensity of the scent is lower in the chemicals exuded by the younger beavers, an older beaver (aged at least 2) might be needed to sufficiently calm the kits.
I wonder if the tolerance for an older subordinate which is not observed in other beaver families in this population could be related to the special needs of this beaver family which has to cope with the aforedescribed disturbances.
I hope to observe this family more often in order to determine their current family structure but also, over time, to see if they have a tendency of retaining offspring older than yearlings (and whether it correlates with food availability per beaver in any given year as the number of beavers in the family changes).
***
Update – Mar 15, 2024. There is at least one kit, born in 2023, in this family (now almost a yearling).
Notes by Ieva 