Spatial analysis of amphibian road mortality levels in northern Portugal country roads

Abstract

Animal mortality caused by vehicle collisions is one of the main ecological impacts of roads. Amphibians are the most affected group and road fatalities have a significant impact on population dynamics and viability. Several studies on Iberian amphibians have shown the importance of country roads on amphibian road mortality, but still, little is known about the situation in northern Portugal. By being more permeable to amphibian passage, country roads represent a greater source of mortality than highways, which act as barriers. Thus, mitigation measures should be applied, but due to the extensive road network, the identification of precise locations (hotspots) and variables related to animal-vehicle collision is needed to plan these measures successfully. The aim of the study was to analyse the spatial occurrence and related factors linked to amphibian mortality on a number of country roads in northern Portugal, using spatial statistics implemented in GIS and applying a binary logistical regression. We surveyed 631 km of road corresponding to seven transects, and observed 404 individual amphibians: 74 (18.3%) alive and 330 (81.7%) road-killed.Bufo buforepresented 80% of the mortality records. Three transects showed clustered distribution of road-kills, and broadleaved forests and road ditches were the most important factors associated with hotspots of road-kill. Logistic regression models showed that habitat quality,Bufo bufo’s habitat preferences, and road ditches are positively associated with amphibians’ road mortality in northern Portugal, whereas average altitude and length of walls were negatively associated. This study is a useful tool to understand spatial occurrence of amphibian road-kills in the face of applying mitigation measures on country roads from northern Portugal. This study also considers the necessity of assessing the condition of amphibian local populations to understand their road-kills spatial patterns and the urgency to apply mitigation measures on country roads.

Effects of Road Density and Pattern on the Conservation of Species and Biodiversity

“…Yet, even within a taxon many of the studies conducted over multiple species found that road mortality was speciesspecific [16,17]. For example, a study that explored variations in road mortality rates of 11 species of mammalian carnivore found that stone martens (Martes foina), European otters (Lutra lutra), and red foxes (Vulpes vulpes) were most frequently documented [18].…”

Wildlife-vehicle collision hotspots at US highway extents: scale and data source effects

“…Examples of analytical approaches and methods include: Nearest Neighbor Index (e.g. Matos et al 2012); 'Satscan', borrowed from epidemiological studies, which looks for non-random clusters of events (i.e. disease outbreaks, Ball et al 2008); the Getis-Ord-Gi statistic for spatial autocorrelation (Getis and Ord 1992); and the Kernel Density Estimator Plus method for estimating locations of high densities of events (Bil, personal communication).…”

Seasonal variation in vertebrate traffic casualties and its implications for mitigation measures

“…Moreover, roadkills are not uniformly distributed; there are usually clusters of casualties that allow hotspots to be identified (Coelho, Teixeira, Colombo, Coelho, & Kindel, 2012;Gomes, Grilo, Silva, & Mira, 2009;Langen, Gunson, Scheiner, & Boulerice, 2012;Malo et al, 2004;Ramp, Caldwell, Edwards, Warton, & Croft, 2005;Santos et al, 2007). Spatial analysis and prediction models have related roadkill impact with roadside characteristics, traffic-related parameters, species richness, and population density (Clevenger, Chruszcz, & Gunson, 2003;Coelho et al, 2012;Espinosa, Serrano, & Montori, 2012;Langen et al, 2012;Malo et al, 2004;Matos, Sillero, & Argaña, 2012;Orłowski & Nowak, 2006;Ramp et al, 2005;Ramp, Wilson, & Croft, 2006;Seiler, 2004Seiler, , 2005.…”