Monday 10 April 2017

Creating an artificial underground hibernation roost in Brittany

Creating an artificial underground hibernation roost in Brittany
Interview: Josselin Boireau, Groupe Mammalogique Breton, (GMB)
by Beatrice Dopita, River Allen Bat Roost.

BD: What inspired the creation of a hibernaculum in Brittany?

JB: In Brittany the places where bats roost are determined by the geology of the land. Granite rocks, open heathland and dispersed areas of woodland make the bats choose sites, like quarries, historic fortifications, and old buildings, which inevitably bring the bats into conflict with man. In certain areas natural roost sites are hard to find and it is for this reason that the Groupe Mammalogique Breton decided to create a series of artificial roost sites for hibernation and for maternity roosts. Brittany has 21 bat species and the GMB has led a series of research projects and mitigation measures dating from the late 1980s. Since 2010 these projects have become more ambitious and artificial roost sites have been created whenever the opportunity has arisen.

The opportunity to build a large hibernation roost in the north of Brittany arose when the quarry company CMGO (Carrière et Matériaux du Grand Ouest) based at Trégeux in the Côtes d’Armor, proposed an expansion of their quarrying activities – permission for the development became linked to this ambitious mitigation project by the GMB and the creation of underground tunnels began under the leadership of Thomas Dubos, colleague of Josselin Boireau.

Photo: Excavation of tunnels

BD: How long did it take to create and what sort of support/guidance did you get?

JB: The project evolved in several phases, the first stage of construction was undertaken by the quarry company over a period of three months then the project was set aside for two years. The next stage of construction involved a company of builders to construct a labyrinth of breeze block walls. This took a further 9 months and was completed towards the end of 2016.

Photo: Breeze block construction.

BD: What were the highs and lows of this project?

JB: Our early attempts to build this artificial roost were very encouraging and seemed to cost very little. The quarry company had offered to do all the excavation work themselves and proposed building the hibernation roost tunnels using materials that were already available on site. The walls were built using breeze blocks laid on the bias with a roof of old telegraph poles; unfortunately, the roof lacked the necessary solidity and the whole structure collapsed! The necessity for the quarry company to invest in more suitable materials brought the whole project to a halt. Construction did not start again until the beginning of 2016. Recent signs that the bats have started to use the new tunnels, just a few weeks after they were built, have given us hope after such a discouraging start to this project.

Photo: Later stage of the construction.

BD: What happens now in terms of maintaining the site and monitoring it for the long term?

JB: We realise that the colonisation of a new site can take some time and now that the tunnels are there we are content to see them evolve and to take advice from experts like Colin Morris, of the Vincent Wildlife Trust, who has already had considerable success with the creation of purpose-built underground roost sites. We are managing the site lightly and minimising any disturbance to perhaps two visits per year. We have installed equipment to measure the humidity and the temperature of various sections of the tunnels so that we can recreate, as much as possible, the conditions in natural roost sites chosen by the bats in this area.

BD: Have you seen any signs that bats have moved in? What were the signs and which species have moved in?

JB: We have already observed bat droppings in the tunnels and butterfly wings on the floor! This indicates that several species of bat are already using the tunnels as a roost. We are hoping to install some passive acoustic detectors so that we can analyse the bat calls to give us an indication of the different species using the roost.

Photos taken in the tunnels showing evidence of use by bats.

BD: What would you say to other groups thinking about creating their own hibernaculum?

JB: The long-term survival of bat colonies depends on the availability of suitable roost sites and on the management of foraging sites around the roost. The creation of suitable cavities, especially for maternity roosts, and of tunnels which provide a constant temperature for winter hibernation roosts is hugely important as bats live for a long time and such projects can prove critical to their long-term survival. Education of the public, conservationists, and those in authority is essential as the preservation of natural roost sites is more important than any mitigation measures that we can devise. It would be a great dis-service to the bats if all we could offer them in twenty years’ time would be a concrete corridor!

BD: Do you have any plans for future developments based on your experience of this project?

JB: We hope to continue with our plans to increase the provision of these artificial roost sites but also to preserve the natural sites which bats are using at the moment, in areas of known bat populations, particularly the Greater Horseshoes. In parallel to this we are encouraging landowners to retain, and maintain, old hedgerows which link roost sites and provide foraging corridors. In
France there is a national programme for preserving areas of biodiversity called “Trame Verte et Bleue” (Green lines and Blue) the aim of this programme is to preserve the connections between areas that are important to wildlife so that animals, and even plant species, are not limited by geographic isolation. This has been incorporated into urban development for several years and wildlife corridors are being established. There is a strong incentive to promote such ideas, not only for the bats, but for all of us who care about the natural world. We are committed to promote ambitious conservation projects like this hibernation roost in Brittany.

BD: Although the GMB is quite a small organisation it is certainly punching above its weight. Their recent publication of the Atlas des Mammifières de Bretagne should be an inspiration to all of us. It is full of maps and splendid photographs, showing the distribution of mammals in Brittany. It is particularly good on bats – be sure to take your bat detectors on holiday and report your finds via their website.

The GMB are giving the bats a voice at regional and at national level in France – we should all be trying to inform and work with our local councils, our MPs, and the general public to be more sensitive to the needs of bats in our local environment.
JB: As for the vast hibernation site in the quarry, come back in ten years’ time and we will tell you how it’s going…

Josselin Boireau                                                         Thomas Dubos


Chargé de mission « Etudes et conservation »                                                              

Actions chauves-souris dans le Finistère - coordinateur du Contrat Nature           «  Micromammifères et Trame Verte et Bleue »
Breton Mammal Group

Beatrice Dopita, River Allen Bat Roost 

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