I am about to describe the territorial arrangement of a beaver family which lives on a segment that has some riparian woodland on one side and hayfield as well as private property (riparian shrubs cleared) on the other side.
I am not perfectly certain how far their range extends.
Downstream, there is a bridge over which quite heavy traffic passes (also, sometimes at night).
Before the bridge, there is an open air restaurant which has set up some distasteful ‘sentimental romanticism’ style terraces etc. along the river.
This sector would be more disturbing and annoying for the beavers.
But if they are not extending the use of their territory downstream (near the bridge and past it), their home range is very small (relative to other families).
My understanding is that their range upstream is cut off rather abruptly and another family’s territory begins.
This other family, as far as I reckon, has been among the first-settlers and their claim is strong.
I believe that I have discovered their boundary because there is a nice spot to watch over the river and when I happen to be noticed by the beavers, they often swim up to me to investigate (if they have the time and curiosity), and the beavers downstream (while sometimes foraging very close to that spot), never swim up near enough – as if there was some invisible barrier between where I was sitting and where they are moving about freely.
The beavers from the upstream family have not been observed swimming there either.
On this side of the river, however, I have not observed much scent-marking activity. Perhaps the boundary is maintained on the other side (because this side is also far more disturbed).
If the family does not utilize areas downstream from the bridge, this would leave the family with about 500 – 600 metres of territory along the river and only half of the territory is optimal.
In fact, one side of their home is highly optimal (a dense riparian forest with very little immediate disturbance) while the other side is highly suboptimal (grass down to almost the very water with some sparse shrubs and plenty of human activity).
Perhaps in order to compensate for the shortness of their range (0.5 metres is not an abnormal range but it is probably not perceived as spacious, either), the beavers have expanded into the riparian forest.
Quite often, when scientists quantify beaver territories, they either delineate them (e.g., 0.5 – 3 km along the river channel) or they make some two-dimensional assessments (including both sides of the river + some 15 – 20 metres of the riparian area).
However, this family, essentially, only covers, let us assume, 500 metres of river channel.
It uses up to 5 metres of riparian area on one side but, on the other side, the family actually uses the entire riparian forest up to the top of its slope (and that would make for about 150 metres if viewed from the perspective of ‘a flying bird’ and for about 200 metres if the slope was included as a distance travelled).
The slope is about 60 – 70°.
And yet, it is even more complicated than that.
Here I have attempted to illustrate the configuration:
There is a ditch between the slope and the channel (about 100 metres from the river).
The ditch is quite wide (at least 2 metres) and also quite deep even during summer (as deep as an average beaver pond – ca. 1 metre).
I suppose the ditch is perceived as a shelter although the beavers have not built lodges on it, nor they seem to have dens near it.
But I think that the ditch serves as a temporary shelter and, due to its presence, the beavers have doubled the length of their territory (500 m along the river + ca. 500 m along the ditch).
The beavers do not appear to forage very far from either the river or the ditch.
Thusly, the riparian forest area between the river and ditch might not be utilized entirely (one would not be advised to draw a simple rectangle from the hayfield side of the river to the top of the riparian slope implying active use of the whole area).
I do not like to intrude in the riparian forest and therefore I am not exactly certain to what extent it is used from the river and from the ditch.
But the other beaver family which also has a bit of the ditch in its territory, seems to use about 20 metres along both the river and the ditch while the middle part (the trees further from both the river and the ditch) are largely untouched.
On the other hand, the slope, in this family, is used almost wholly as there are beaver cutting marks at the top of the slope verging with the arable field.
Personally, I have come by an impression that beavers perceive slopes (which, to us, seem more precarious than flat areas) as less dangerous, nor they are aggravated by the effort to having to climb up the slope.
Thusly, it is curious that the beavers would not forage in the relatively dense growth between the river and the ditch (further than ca. 20 metres of either body of water) but they would climb ca. 50 metres upslope (the ditch lies immediately at the foot of the slope and thereby the top of the slope would also be about 50 metres from the ditch).
Such behaviour suggests that beavers might find it easier to travel across dry land which is sloped (rather than flat).
Perhaps the motor activities involved in swimming also ease travel up a steeper slope.
And perhaps the beavers feel more secure if they can make escape downslope rather than across a flat area.
Therefore, they might risk to venture further from the shelter (water) if the journey leads up the slope.
All in all, to combine the estimates, this beaver family might have a territory of about 500 x 2 metres when measured linearly (500 m along the river + 500 m along the ditch although the ditch is not very straight and the total metrage could be longer); of about 500 x 160 = 80 000 m2 when measured as a total area (without accounting for the actual travel up the slope); or of about of (5 (hayfield side of river) + 5 (river) + 20 (riparian forest near the river) + 20 (riparian forest near the ditch) + 2 (ditch) + 50 (riparian forest slope on the other side of the ditch)) x 500 = 51 000 m2 actively used range.
This actively used range could be termed ‘core area’ but it would be misleading.
‘Core area’ is the area within home range that the beavers use most of the time (e.g., half of the time) but these 51 ha are not used as intensely on a uniform basis.
The range still has some preferred patches. vs rarely visited patches.
For example, it is clearly seen that the hayfield side of the river is visited seldom and while I have included it in the home range estimate, it is not a core area.
The family, thereby, sort of has a unique situation with its ‘true home’ (river where denning occurs) and some type of ‘outhouse’ (the ditch where denning does not occur but where shelter can be sought temporarily during the nightly foraging activity).
The ditch has allowed the family to compensate both for the shortness of their territory along the river channel as well as for the suboptimal habitats on one side of the river.
Without the ditch, the family would likely forage ca. 5 metres on one side of the river and perhaps up to 50 metres along the other side (the necessity to obtain food would likely cause them to venture further from the river than 20 metres) but they would probably find it too stressful to reach the top of the slope (or they might travel as far but it would cost them more due to psychological pressure and the need to carry the forage down to the river rather than down to the ditch).
The family would thereby be restricted to ca. (5 + 5 + 50) x 500 = 60 x 500 = 30 000 m2 of area of active use (with occasional ventures beyond this area) which is by 40% smaller than the area they are currently able to utilize regularly.
This family is not the only beaver family that I have observed foraging on ditches.
However, out of the other two families known to me, one family actually lives in the ditch and the other family travels the ditch which is adjoined to the river channel (where they live) and which is not dissimilar to a river tributary.
The ditch on this family’s range is not adjoined to the river and runs rather parallel to it.
I have not yet seen another beaver family which has such home configuration whereby the two main bodies or water are disconnected one from another and they serve the purpose of the penetrating the inland further.
This family regularly forages up to 200 metres from the river channel (which is ca. 40% of the length of their territory) while other families who have incorporated ditches into their home, could not be described as venturing as far inland because they keep close to the river channel or the ditch but, as the ditch is not parallel and it is adjoined to the river channel, their home layout is still rather linear.
Note – I would like to read more about beavers and slopes 🙂 I think that beavers are relatively undaunted by slopes both with respect to travel upward and the prospects of speedy descending downward (in the case of making an escape).
However, I have also had observations which suggest that, in some situations, beavers might attempt to conserve energy while foraging on a slope Beaver observations – Feb 9 and 10, 2024 (exemption to central-place foraging).
I believe the difference might be concealed in the resources available on the slope.
In the instance of beavers ‘not being overly bothered by the slope’, large trees and larger stems of shrubs were accessible to them.
In the latter instance when beavers seemed to try to spare extra effort, only very thin shrubs or saplings were available and the riverside itself did not provide a convenient bank where to settle down the slope.
***
Of course, the estimates given here should be perceived as generalized approximations rather than actual measurements.
Firstly, I cannot access the most part of this beaver family’s range.
Secondly, the river is not straight while I have painted the picture as if it were.
Thirdly, the riparian slope through this area exhibits contrasting distance to the river channel (in most spots it is quite far but there is a segment where it comes much nearer and in this segment the ditch is not strictly parallel to the river, either).
I simply wished to illustrate how the beaver family had significantly increased their range not along the river channel but through the appropriation of an additional water feature (that is not connected with the river) into their territory.
Notes by Ieva 