Movement of small mammals across divided highways with vegetated medians

Previous studies suggest the gap in forest cover generated by roads contributes to the barrier effect of roads on movement of forest-dwelling small mammals. However, it is not known if vegetated medians of divided highways affect movement of small mammals by reducing the effective highway width. The purpose of our study was to determine whether the type of vegetation cover in the median (treed or grassy) or median width affects small-mammal crossings of divided highways. At 11 study sites varying in median cover type and width, we live-trapped small mammals next to one side of the highway and translocated them to the opposite side of the highway using a standardized translocation distance. In total, 24% of translocated individuals were recaptured on the side of the highway of initial capture, i.e., they had moved across the entire highway. This was significantly lower than what would have been expected in the absence of the highway (58%). The overall probability of recapturing a translocated individual was not significantly related to median cover type or width. Our results suggest that efforts to mitigate the barrier effect of highways on small mammals cannot be accomplished by al- tering median vegetation type and width. Resume : Des etudes anterieures laissent croire que les trouees dans la couverture forestiere formees par les routes contri- buent a l'effet de barriere des routes sur les deplacements des petits mammiferes forestiers. On ne sait pas, cependant, si des terre-pleins centraux de vegetation dans les routes divisees affectent les deplacements des petits mammiferes en reduisant la largeur effective des grandes routes. Le but de notre etude est de determiner si le type de couverture vegetale (arborescent ou herbeux) et la largeur du terre-plein central affectent la traversee des routes divisees par les petits mammiferes. A 11 sites d'etude presentant une variete de types de couverture et de largeurs du terre-plein central, nous avons piege des petits mam- miferes vivants pres d'un cote de la grande route et les avons relocalises sur le cote oppose a une distance standardisee de deplacement. En tout, 24 % des individus deplaces ont ete recaptures du cote de leur capture originale, c.-a-d. qu'ils ont tra- verse toute la route. C'est un pourcentage significativement plus bas que celui attendu en l'absence de grande route (58 %). La probabilite globale de recapturer un individu deplace n'est pas reliee significativement au type de couverture, ni a la lar- geur du terre-plein central. Nos resultats font penser que les efforts de mitigation de l'effet de barriere des grandes routes sur les petits mammiferes ne peuvent consister en une modification du type de vegetation et de la largeur des terre-pleins centraux. (Traduit par la Redaction)