Drainage culverts as habitat linkages and factors affecting passage by mammals

Abstract

Summary1. Drainage culverts are ubiquitous features in road corridors, yet little is known about the efficacy of culverts for increasing road permeability and habitat connectivity for terrestrial wildlife. Culvert use by small-and medium-sized mammals was investigated along roads in Banff National Park, Alberta, Canada. An array of culvert types was sampled varying in dimensions, habitat and road features during the winters of 1999 and 2000. Expected passage frequencies were obtained by sampling relative species abundance along transects at the ends of each culvert. 2. Weasels Mustela erminea and M. frenata and deer mice Peromyscus maniculatus used the culverts for passage most frequently, whereas red squirrels Tamiasciurus hudsonicus and snowshoe hares Lepus americanus were the most common small mammals in the study area according to transects sampled near each culvert. 3. Species' performance indices (observed crossing vs. expected crossing) were calculated for five species by comparing their tracks inside and adjacent to 36 culverts. Culvert performance indices were significantly different between the five species: culvert attributes influenced species' use but different attributes appeared to affect use by different species. 4. At all scales of resolution (species, species group and community level), traffic volume, noise levels and road width ranked high as significant factors affecting species' use of the culverts. Passage by American martens Martes americana , snowshoe hares and red squirrels all increased with traffic volume, the most important variable. Coyote Canis latrans use of culverts was negatively correlated with traffic volume. Increasing noise and road width appeared to be negative influences on culvert passage by coyotes, snowshoe hares and red squirrels. 5. Structural variables partially explained passage by weasels and martens. Weasel passage was positively correlated with culvert height but negatively correlated with culvert openness. Martens preferred culverts with low clearance and high openness ratios. High through-culvert visibility was important for snowshoe hares but not for weasels. The passage by weasels and snowshoe hares was positively correlated with the amount of vegetative cover adjacent to culverts. 6. For many small-and medium-sized mammals drainage culverts can mitigate the potentially harmful effects of busy transport corridors by providing a vital habitat linkage. To maximize connectivity across roads for mammals, future road construction schemes should include frequently spaced culverts of mixed size classes and should have abundant vegetative cover present near culvert entrances. Further work is required to assess the effects of culverts on population demography and gene flow adjacent to large roads.

Surveying drainage culvert use by carnivores: sampling design and cost–benefit analyzes of track-pads vs. video-surveillance methods

“…Despite the growing interest in measuring the effectiveness of crossing structures for fauna to increase road permeability (e.g., Yanes et al 1995;Clevenger et al 2001;Grilo et al 2008;Mata et al 2008), there is an uncertainty when determining the most appropriate method to best evaluate their effectiveness. In fact only one study has compared the passage delectability among the methods, as well the cost-benefit for each method (Ford et al 2009).…”

“…Increasing landscape permeability and minimizing animal-vehicle collisions (AVCs) are therefore key issues to be considered during road construction and improvement projects (Iuell et al 2003). The adaptation of incidental crossing structures built for other purposes (e.g., culverts to allow water passage under the roads) is one possible solution to restore animal movements across roads and its role has been widely investigated (e.g., Ascensão and Mira 2006;Clevenger et al 2001;Mata et al 2008;Taylor and Goldingay 2003;Yanes et al 1995).…”

Spatial Heterogeneity, Not Visitation Bias, Dominates Variation in Herbivory

“…Repeated visits to the plants create paths through the vegetation, potentially making plants more visible and accessible to deer. Other studies suggest that mammals tend to travel on pre-existing paths such as roads or ditches (Clevenger et al 2001).…”

Roads and macropods: interactions and implications

“…Although fauna-exclusion fencing may reduce wildlife-vehicle collisions where it is present on both sides of the road, it can also cause road-kill hotspots at the fence ends (Clevenger et al 2001a). Additionally, on occasion when an animal may breach the fence, they then become trapped on the roadway unless one-way escape gates or ramps are installed at …”