Recently I have realized that the count of beavers per colony and per specific territory which I have obtained through direct observations (visual observations of beavers swimming and/or feeding) during summer and autumn correlate rather well with the tail splashing events and intensity during late autumn and winter.
Not all beavers can be met during a single walk along a particular river segment, however, I should say that two to three walks would ensure a rather accurate count of the number of beavers per that segment.
Three walks might be needed in sites where access is restricted and where not all riparian segments can be visited due to, e.g., nature conservation or physical barrier issues (because some beavers during the survey might be hiding in those particular segments which is even likely as these segments are often more secluded and undisturbed).
Coincidentally, beaver kits (born this year) have also commenced tail-splashing since perhaps October.
It is quite easy to tell whether the splash was made by a kit or an adult beaver and I even believe that juveniles (yearlings and two-year-olds) might create a slightly quieter splash than full-grown adults (this might also depend on dominance status, not just size alone).
Accordingly, listening in on tail-splashing might offer some insight into the colony size and distribution but also colony structure (age structure) as louder and more intense splashes are made by adults compared to younger, subordinate individuals.
Thus, I began wondering whether such surveys might be applied in order to monitor local beaver populations.
This method would be less invasive and more financially feasible than radiotelemetry and capture-recapture studies.
Certainly, it implies some disturbance to the beavers but I do not suppose that energy expenditure during a single tail-splash (or a short sequence of splashes) is enormous and would threaten the animals.
Nor I suppose that stress levels would be very high if the surveyor simply moved on along the shore instead of staying in the area.
Such monitoring method would probably involve walking without attempting to conceal one’s presence but also without announcing it ahead of time.
That is to say, beavers should be able to notice the surveyor’s presence in order to react to it by producing a splash but, at the same time, beavers should not be able to anticipate the presence while the surveyor has not approached them closely enough because, under such circumstances, the beaver would probably swim off rather than splash (especially, if the related individuals that the beaver is attempting to warn are located in the direction opposite than that of the approaching surveyor and thus the beaver predicts that the surveyor is moving away from its family and not toward it).
The walking manner should thereby not be conspicuous but also without special effort to make no noise and to evaluate wind direction.
If beaver size (age) and dominance status, indeed, affect the audial qualities of the splash (which could be determined through studying individuals of known age, size and status), a device could be invented that allows to detect the splash and analyze the sound parameters in order to produce a prognosis regarding the beaver’s age and social status.
I believe that humans could rather easily distinguish between kits and adults without any technological aids but the difference between kits and yearlings as well as yearlings/subadults and adults might be more subtle but within the scope of sound input processing devices.
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A brief comment to note that any such monitoring would be more difficult during the period when beavers are about to give birth to kits.
Currently (near parturition time), I have observed that it is more challenging to distinguish between size and age/status groups based on slapping behaviour because all families seem to be invested in making splendid splashes and the last year kits are apparently so enthused over their independence and their new role as protectors in the family that they splash nearly as vigorously as their parents.
They sometimes even swim off to repeat the splash if the first splash did not carry due to shallow water or other location-related difficulties.
It is still possible to tell a kit (yearling) from an adult (listening carefully), however, it is not as obvious as during previous periods.
Thus, spring monitoring should be planned shortly after ice has melted but before kits are about to be born.
Additionally, nearing parturition it seems that adult females might not be physically able to or might not be willing to invest much energy in tail-slapping and their slaps have become equal to those produced by last year’s kits.
Notes by Ieva 