Dormice at Rhos Cefn Bryn

2012 was an exceptionally wet year with above average rain, which made for poor monitoring numbers of dormice recorded for the National Dormouse Monitoring Programme (NDMP).

Only four adult male, four adult female, one juvenile male and two juvenile female. In June a failed brood of four young greys were found dead in a drain pipe nest box, due to the inclement weather and cool climatic conditions.


Dormouse monitoring

Dormouse monitoring

The spring came early this year with a mild spell in March. I undertook the first dormouse monitor on the 9th March and there were unoccupied wood mouse nests and evidence of possible dormouse hibernation emergence activity in one nest box, with whole old leaves in.

The icy grip of winter reclaimed the mild early spring with plummeting temperatures. The prolonged winter freeze continued, not relenting until the very end of April. I think we are all agreed that this set back all flora and fauna by a month (may be more) throughout the entirety of 2013.

However, I believe that for the local dormouse population status, it proved to be a serious set back indeed. The early mild period of March would have encouraged dormouse hibernation emergence, only to go back into deep torpor when the temperatures fell along with the snow.

Many dormice, adult and juveniles, must have perished in the harsh conditions, due to depletion of body fat reserves.

In May the first juvenile male weighing in at a respectable 21g, after the prolonged cold winter period.

In June a juvenile female of only 14g was recorded.

New nest boxes supplied by the Peoples Trust for Endangered Species were installed at the beginning of July and we hoped for better monitoring results as the old ply boxes were wet inside and generally dilapidated.

So other circumstances such as the old nest boxes have to be considered as a contributing factor towards this year’s low-recorded numbers as well as the new timber boxes possibly off putting to the dormice.

On the 8th June as the volunteer reserve warden I conducted a walk and talk through the wood at the reserve with Butterfly Conservation Wales, we did not see any dormice in the hot early afternoon but the marsh fritillary butterflies were flying in high numbers, absolutely magical!


Dormouse by Bev Lewis (BWT)

Dormouse by Bev Lewis (BWT)

We actually had a wonderful summer this year and July brought temperatures up to 28 degrees! The heat wave also affected dormouse behaviour and I started to notice holes appearing in the ground that I believe to be dormouse activity as they were probably burrowing to nest under hazel stools and other tree roots for a stable nest temperature during the heat wave. The holes are larger than bank voles and in open ground as opposed to bank vole burrows situated on the side of banks/ridges etc.

Dr Wendy Harris, my accredited agent enlisted Charlotte to come along from Swansea University with an endoscope to investigate, but alas we did not find a dormouse and it was a wet day.

This year’s dormouse recorded numbers in nest boxes so far, have been lower than the wet year of 2012. This is certainly due to the prolonged winter and loss due to low body fat reserves. Dormouse activity has been noted on / in the ground burrowing and Rhos Cefn Bryn provides good environmental habitat. The old nest boxes were in poor habitable condition and the late replacement of the new nest boxes made for a dire, monitoring year.

It is accepted that the natural population status of species fluctuation is fact, but throughout this year, it has been my concern that a localised dormouse population crash had occurred in April…

On Saturday 19th October we began to notice dormouse nests of poor construction with whole loose leaves in quite a few nest boxes. I commented that it was probably juvenile activity from late breeding, and thankfully I was proved to be correct!

We went on to record three maternity nests with the mother and juveniles and many more dormice recorded to a total of thirteen dormice!

The breeding occurred in natural nest sites, probably in underground burrows and the mothers have led their pups to nests in the boxes!

Late breeding at Rhos Cefn Bryn saves the day!

We will return in November to monitor the weight of the juveniles, as some were borderline to survive the oncoming winter at 14.5g.

Richard Pond