Factors influencing the discovery and use of wildlife passages for small fauna

Abstract

While many studies have looked at how large mammals respond to road mitigation measures, few have examined the effects on smaller mammals. We investigated the effectiveness of three different types of wildlife passages along Highway 175 in Quebec, Canada, for small- and medium-sized mammals (<30 kg) using infrared cameras. Wildlife passages (n = 17) were monitored 24 h a day 7 days a week from 2012 to 2015. Two research questions were addressed: (i) What influences passage discovery and use? and (ii) does it differ between species? Global and species-specific models were produced for both discovery and use. A linear mixed-effects model was used for the discovery data (log-transformed counts), and a generalized linear mixed model was used for the crossing data (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 significantly more likely to be discovered by micromammals and wooden ledge culverts by red squirrels Tamiasciurus hudsonicus. Older passages were discovered less in general, with the exception of marmots. Marmots were also the only species to show a difference in crossings 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 spp. Synthesis and applications. By separating animal responses to wildlife passages into two types (discovery and use), we have shown it is possible to incorporate multiple dimensions into post-mitigation evaluation. This study highlights how transportation agencies can engineer more effective wildlife passages by minimizing the barrier effect of the structures themselves and constructing more passages better suited to the needs of the species they are targeting. To benefit the most species, it is recommended that future projects contain a diversity of open, single segment passages requiring long-term monitoring.