Talk Use by large mammals of wildlife crossing structure on an overpass in western France Results of the first three years of cameratrap surveys

In 1981, the A10 highway was going through the Lande forest, making a nearly impossible to cross barrier for large wildlife.

Back then, a "wild game passage" had been set up in the town of St Ciers du Taillon. Despite its appropriate location, the bridge with its narrow operational width of 4.50 meters was little to not frequented.

In 2012, aware of this problem, ASF widened the deck of this former passage by building an overpass (landscape bridge) with an operational width of 18.50 meters.

Functional since July 5, 2012 the Fédération des Chasseurs de Charente-Maritime is in charge of monitoring the large fauna use of this facility.

This monitoring is ensured by the installation of two "camera trap" devices.

One score unit corresponds to an animal’s complete crossing of the facility which, depending on its behaviour, may result in one shot or hundreds, in case of feeding behaviour for example.

Over the three-year monitoring of 4180 crossings, close to 100 000 shots have been processed. These concerned the sole species of deer (Cervus elaphus), roe (Capreolus capreolus) and boar (Sus scrofa) and permitted the gathering of highly instructive data.

Based on these information, we were able to compile an accurate and significant analysis of parameters for each species, like the importance and direction of movements, monthly variations, schedules...

The number of recorded crossings for the roe increased steadily by 245% over the three-year period (from 101 to 248 crossings). Concerning boars, the yearly average of 191 crossings fluctuates according to the population level.

For the deer, the most represented with a yearly average of 1021 crossings, the results are unmatched in the records and enable a finer analysis by gender and year-class: decrease in the annual crossing frequency for does and youngsters while we note a strong increase for stags.

Globally, all species combined, the analysis of crossing numbers by time window shows that animals tend to go over the passage earlier.

The exchanges for the three species are relatively balanced between both sides with now one and only deer population on the whole massif and a genetic diversity broader than ever.

The cross-checking of data with light counting, as well as the continuous monitoring has enabled to reassure local hunters, originally reluctant before the overpass construction. Indeed this "landscape bridge" contributes to a rational population management.

These data confirm the intensive use of the facility and its critical importance when it comes to crossing highways for large-range species (1111 crossings for the deer in the first year).

The building of an overpass such as this one also contributes to diminish the penetration of fauna on the network.

overpass, monitoring, deer, large range species, exchanges, rational population managment