Evaluating the effectiveness of wildlife passages for small and medium sized mammals

Abstract

While many studies have looked at how large mammals respond to road mitigation measures, few have examined the effects on smaller mammals nor taken a multispecies approach. I investigated the effectiveness of three different types of wildlife passages along Highway 175 in Quebec for small and medium sized mammals (<30 kg) using infrared cameras. Wildlife passages (n=17) were monitored year round from 2012 to 2015. Two research questions were addressed: (1) Does discovery and use differ between passages and if so, why? and (2) Are there differences between species? Global and species-specific models were produced for both discovery and use. A linear mixed-effects model was used for discoveries (log-transformed counts) and a generalized linear mixed model was used for usage (binary response). Species’ responded to the passages differently, with discoveries increasing overall and in particular for marmots (Marmota monax) as latitude increased. Pipe culverts were more likely to be discovered by micromammals and wooden ledge culverts by red squirrels (Tamiasciurus hudsonicus) than other passage types. Older passages were discovered less in general, with the exception of marmots. Marmots were the only species to show a difference in use by passage type, favouring pipe culverts. Passage use was less likely with a median present for all models, except squirrels. More open passages had higher use overall and particularly for marmots and weasels (Mustela sp). In contrast to previous studies, distance to cover and the presence of light were not important predictors. Agencies can engineer increasingly effective wildlife passages by minimizing the barrier effect of the structures themselves and constructing passages better suited to the needs of the species being targeted. To benefit the most species, it is recommended that future projects contain a diversity of open, single segment passages requiring long-term monitoring