The local wildlife center agrees that it's a hazel dormouse, but a bit strange that it isn't hibernating yet. It must be using the feeder to finish fattening up. Some research turned up that they are not nuisance rodents as they never go inside homes.

They are extremely rare and considered to be threatened in many parts of their range in Europe due to habitat loss (hedgerows and woodlands with a dense understory). As such they are on the national red list (protected species) in a number of European countries and can't be killed or caught. I was surprised to read that in optimal habitat conditions their numbers are only about 10 individuals per hectare!

Good for you Camille for that research. Just another Stone in the wall of what human beings have done to the Earth and Wildlife.