Glis glis, the edible dormouse

I attended a talk last night at the Natural History Museum in Tring all about glis glis. It was given by Roger Trout who has spent years monitoring the glis glis in the Chilterns, by micro-chipping and radio tagging them.

Things I found out about glis glis:

1. Glis glis, or the edible dormouse, is a non-native species that escaped from the Tring Park private collection of Baron Rothschild in 1902. (See Lord Rothschild for more about him.)

2. They've made themselves very at home in the Chilterns and the population is now estimated at around 30,000. They haven't spread far from Tring and are only found within the Chilterns (bound by the M1, M25, M40 and the Chiltern scarp), although there are a few (worrying) cases of them being found further afield now.

3. They're called edible dormice because the Romans used to catch them and keep them in terracotta pots, fattening them up ready to eat.

4. They are long lived animals. The oldest glis monitored this year was 14 and last year they had 2 breeding females that were 13 years old.

5. They are considered a real pest for a number of reasons:

• They predate hole nesting birds (such as blue tits and great tits), getting in the nest boxes eating the eggs, chicks, fledglings and even the adult birds.
• They use bat boxes and there have been cases where bat monitoring sites have had to remove the boxes due to the glis, meaning they can no longer monitor the bats.
• They use boxes put up for the native hazel dormouse and the number of hazel dormice in the Chilterns seems to be decreasing as the number of glis increase.
• The biggest nuisance though is to people as they get into houses, crash around in peoples lofts (in the middle of the night), get into water tanks and drown, raid kitchens for food, eat insulation and generally cause chaos and havoc. The strange thing is that they will go into one house (a record was 296 removed from one cottage in one year) but the house next door will be completely clear of them. Nobody is sure why they go into houses, or why they go into some but not others.

6. Glis have breeding years (with an average of 6 young in a litter) and non-breeding years, which seem to coincide with the tree flowering years. When the trees don't flower well, none of the glis breed, presumably because there won't be enough food. In fact those years, the glis are hardly seen at all in the monitoring programme and it's believed that they could hibernate all the way through the summer and the following winter (meaning they hibernate for 18 months). This is yet to be proved though.

7. They hibernate in a small chamber, 1m - 2m underground and the chamber is completely sealed so that foxes and badgers don't get any scent from them. When they hibernate, their body weight increases from around 120g to 300g, their heartbeat drops to 8 - 10 beats per minute and they breathe about once every 5 minutes.

8. The most glis found in a single monitoring session was 750, as opposed to hazel dormouse monitoring where you would be lucky to see 10. People come from all over the country to help with the monitoring and helpers from mammal groups turn up from as far afield as Cheshire. Seems like the glis in the Chilterns are such a novelty that they love coming to see them.

9. If you catch a glis in your house it is illegal to let it go again and you must kill it humanely.

10. I've never seen one and I'm very glad they aren't in my attic!