Sunday, 24 May 2009

Scent Mounds and Maternity Units

Peter Collen of the Marlab freshwater fisheries' research station at Pitlochry ( came to see me on the 20th May. I had hoped that he was going to electro-fish in the stream. Unfortunately, he thought that the water was too turbid as a result of the recent rains, so he did no fishing. However, we walked the length of the water course that has been and is occupied by beavers.

Among many topics discussed, he asked if I had ever noticed any scent mounds. I had not, so far as I knew, but the next day after Peter's visit I noticed the powerful scent of beaver and, looking down, saw a piece of matted vegetation that had been left on the bank of the burn. I kneeled down to smell the object and breathed in the powerful scent of beaver.

Scent mounds are used by beavers to indicate to other beavers that they are occupying the territory. In the past I have noticed the scent of beavers from time to time, but this was the first time I have been able to place the scent. Beavers place these olfactory signal stations through their territories, where they serve as warnings, but also let other beavers know various bits of information about the beavers whose ground they are crossing, or sniffing from a distance.

To make a scent mound a beaver scrapes together some mud, or vegetation, places it on the bank of the stream and then, squatting over the mound squishes scent from its anal glands and castor sacs onto it.

The subject of beavers and their use of scent is a big one and anyone who is interested in it should refer to the work of Dietland Müller-Schwarze and Frank Rosell.

The second half of May is birth time for beaver kits. Last week a student from Edinburgh University, who is doing an MSc., came to sample water from the beaver stream in order to compare the chemistry of the water above and below the dams.

He came and asked me if beavers were often to be seen out by day. I replied that such a thing was unusual, though not impossible, so we went and looked and found the beaver in question, pretending not to be there. We left the site.

About two hours later I returned and found the beaver digging a burrow. I thought that this must be a female digging herself a burrow in which to give birth.

However, I had heard both that females find themselves a temporary home in which to give birth and that males are expelled from the main burrow and leave the female behind to give birth.

I checked with Bernard Richard's book 'Les Castors' (Balland 1980) and he writes «La femelle de son côté aménage l'abri où vont naître les jeunes, tandis que le mâle fait de même dans l'abri provisoire où il va passer quelques mois, d'avril à juillet environ».

'The female for her part arranges the shelter where the young will be born, while the male does the same in the temporary shelter where he will spend several months, from April to about July'.

Given that families of beavers often have a number of burrows and lodges within a territory the question of who moves and who stays is not as clear as if there were only one main lodge.

I wonder if anyone reading this blog has anything to suggest on the subject of who lives where during the time that the female gives birth.

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