From our experience with uninvited furry guests, and what we have heard, the basic principle is that these invaders are looking for peace and quiet, warmth, food and water. If they install themselves in ones attic, one has the choice to 1) kill them 2) persuade them to move house (a particularly neat option if you don't get on with your neighbour).
For us, the cat worked well. It just scratched around for a while, and all uninvited guests soon smelled the presence of another animal.
They say you can do this with radio (France Inter), high frequency tone device, cologne, lights and movement detector, etc etc just stuff which will make the animal uncomfortable enough to look elsewhere.
I stand corrected - I had in my head breeding was during Spring so I went and double checked.
"Beech Martens breed between June and August and after a gestation period of 7.5 - 9 months, which includes a 6.5 - 8 month period of delayed implantation, 2 - 4 young are born."
The mothballs could end up an old wives' tale but if it works, yay, (cheapish) harmless option. I should think the stinkier the better as long as you don't have to go up there repeatedly yourself - boules de naphtaline
Thank you. I didn't know about the spray. Unfortunately I'm in the Vienne so not too close to Alsace or Ardennes. Should have said that in the original post but I always seem to forget to do that!
Mothballs! Apparently they can't stand the smell and move out quite quickly. I think you'd need to try it quickly though as it's breeding season (March/April) so if mum's already nesting she might simply put up with it.
I have seen anti stone- & pine-marten spray on sale in garages in Germany, you put it on your car so they won't come & tear out the wires in the engine. It must be obtainable in France eg in Alsace or the Ardennes where they would be common.