Green crossings over French roads saving wildlife
Construction company Vinci has spent €177million building 200 animal passages in the last decade. Jane Hanks finds out how they save wildlife
Clever bridges and tunnels have been saving the lives of deer, badgers and wild boar as they cross the nation’s motorways.
There have been passages for animals since motorways were introduced but, in the past 10 years, they have become more sophisticated and adapted to the needs of the animals using them.
Road-kill bears testimony to the continuing massacre of wildlife but the carnage is reducing thanks to these innovations.
Wooden silhouettes of wild boar and deer decorate the sides of the bridges across motorways, marking the increasing number of écoponts, built to allow wild animals to cross in safety.
Vinci has built and manages two-thirds of French motorways and is responsible for 4,400km of road, which often slices through woodland and countryside.
Since 2010, Vinci says it has become France’s biggest spender on ecological structures, putting €177million into creating 200, including 20 new-style bridges and 110 tunnels or écoducs.
Vinci environment manager Sophie Sallanne said the new bridges have features to attract animals of all sizes.
Before, they were a classic bridge with Tarmac and a green strip on each side. Now they are dedicated to wildlife.
“At up to 25 metres across, they are wider than previous bridges,” said Ms Sallanne. “That is necessary to attract red deer. Deer are timid, and only a few crossed the old, narrower bridges, but they use the new ones.
“We have worked with wildlife associations, such as the ONCFS (Office National de la chasse et de la faune sauvage) and the LPO (Ligue pour la protection des oiseaux) to design the bridges. On the edges, the écoponts have high wooden fencing, so the animals cannot see the motorway.
“They can hear it, but it has been shown this does not put them off.
“Hundreds of species of local bushes and trees are planted on each one to provide continuity between the landscape on each side. Some are deliberately planted in a line, because bats like to follow an uninterrupted structure to pass from one side to the other.
“There is another line made of piles of rock and wood, which encourages small rodents and amphibians to cross, so they are not exposed in an open space.
“There are small ponds for frogs, snakes and toads. At each side, trees and fences are installed to direct wildlife on to the bridge.”
Ms Sallanne said they also study where to put the bridges: “We look at the most likely places where animals will want to cross. It has to be in a technically possible place.
“The purpose of the bridge is to make sure that populations of animals can mix and that there won’t be more on one side than another and that species will have a bigger area at their disposal to live in.”
Between February 2011 and April 2015, the first in-depth study was carried out on 81 structures on 12 motorways in 13 departments to see how effective the wildlife passages were. Different types of infra-red and movement- sensitive cameras were used.
As well as the bridges, there are several tunnels under the roads.
Where waterways are diverted under the motorways, concrete ledges are installed.
The study found that the écoducs, which are the most common form of crossing, were used on average 300 times a year by 25 species of mammals, five species of amphibians and reptiles, and three species of birds. Wild boar and smaller deer also used the tunnels.
The tiniest animals were difficult to detect, so there are no figures.
Ledges along waterways were used less but did attract otters, weasels, polecats and pine martens, while hedgehogs, badgers, genets and coypu preferred the dry tunnels.
The greatest success on the bridges was red deer with, on average, just over 1,000 crossings a year on each bridge.
It was more difficult to detect the smaller mammals on the bridges because of their tendency to hide in the vegetation and rocks, but photos were taken of
16 species of mammal.
Some animals do take longer than others to get used to a new passage. Hedgehogs, otters and wild boar can take more than a year to dare to cross, while a fox will take just three months.
“You can see on the video recordings how it works,” said Ms Sallanne. “First, one of the most adventurous animals will be curious and give it a go, and
then others will follow.”
She says they have learned a great deal in the past few years, even to the extent of diverting streams.
“In the first motorways, water would just be channelled into a straight, concrete-lined conduit.
“Now we use several techniques to make a new waterway as natural as possible, creating meanders, putting rocks and soil on the bed, and planting along the banks.”
Another specialist passage is one for bats, called a chiroptéroduc.
Bat populations find it difficult to cross motorways, as they appear as empty spaces to them so they cannot use their high frequency sonar system to navigate in the dark, and they can easily lose height and be killed by lorries.
Over some motorways you can now see metal corridors, decorated with silhouettes of bats, high above the road.
They are still being studied to see which type works best.
Each structure is a technical challenge.
One of the most recent is the Ecopont du Causse, near Périgueux, which opened in November 2017 on one of the newest motorways – the A89, which links Bordeaux with Lyon.
It is 25 metres wide and 55 metres long and has, at different points, between 30 and 90cm of soil on it and 600 different bushes and trees.
It took 10 months to build.
The LPO is convinced of the efficacy of these structures, saying it helps reduce the deaths of thousands of animals and birds on the roads. It points out that for certain rare species, such as the otter and the mink, traffic is the main cause of death.
One of the triumphs for the LPO was a photograph of an otter and her three babies crossing the A10 using a tunnel.