Factors affecting road mortality and the suitability of road verges for butterflies Piotr Skórka a,⇑ , Magdalena Lenda b , Dawid Moron ´ c , Konrad Kalarus d , Piotr Tryjanowski a a Institute of Zoology, Poznan University of Life Sciences, Wojska Polskiego 71 C, 60-625 Poznan, Poland b Institute of Nature Conservation, Polish Academy of Sciences, Mickiewicza 33, 31-120 Kraków, Poland c Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Slawkowska 17, 31-016 Kraków, Poland d Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland article info Article history: Received 30 July 2012 Received in revised form 10 December 2012 Accepted 20 December 2012 Keywords: Cars Habitat fragmentation Insects Landscape Mortality abstract Little is known of the impact of roads on insect mortality. This is a significant gap, because road verges are regarded as an important tool for insect conservation. In this study, we investigated which factors affect the number of roadkills in grassland butterflies and, simultaneously, the species composition and abun- dance on road verges. We established sixty transects, two hundred metres long, on roads in farmland areas and with differing traffic volume. Each transect consisted of two parallel lines, one on either side of the road. Ordination methods showed that the species composition of the butterflies killed on the roads was primarily explained by the species composition of those living on the road verges. At least 6.8% of the butterflies were estimated to end up roadkilled. Also, the number of species and abundance of butterflies killed on the roads were positively dependent on both the abundance of butterflies on the road verges and on the traffic volume, but negatively correlated with the richness of plant species on the road verges. However, the proportion of individuals killed was negatively linked with the abundance of butterflies on the road verges, the richness of the plant species and the share of grassland in the land- scape. There was a statistically significant tendency for small-bodied species to be overrepresented in the roadkill samples. Our results indicate that the verges which were of high conservation value for but- terflies suffered the least from road mortality. The sowing of plant species, less frequent mowing and maintaining a high grassland cover in the vicinity of roads are recommended conservation actions for the improved conservation value of road verges for butterflies. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction The development of road networks and increased traffic volume is one the most significant causes of habitat fragmentation (Forman and Alexander, 1998; Trombulak and Frissell, 2000; For- man et al., 2003; Fahrig and Rytwinski, 2009; Selva et al., 2011) that has lead to decreased populations of many animal species (Warren et al., 2001; Fahrig, 2003; Forman et al., 2003; Thomas et al., 2004; Biesmeijer et al., 2006; Silva et al., 2012). Several stud- ies, mostly carried out on mammals, amphibians and some insects, indicate that roads dividing habitat fragments may be an obstacle to the movements of individuals and, therefore, to the gene flow between the fragments (Bhattacharya et al., 2003; Shepard et al., 2008; Smith-Patten and Patten, 2008; Jackson and Fahrig, 2011; Soluk et al., 2011; Neumann et al., 2012). On the other hand, many studies indicate that the negative effects of roads may be mitigated by the high conservation value of road verges (a strip of grass or other vegetation beside a road) or other habitats associated with roads (Ries et al., 2001; Saarinen et al., 2005; Valtonen et al., 2006, 2007). Road verges may serve as dispersal corridors and be a suitable habitat for many insects (Forman and Alexander, 1998; Trombulak and Frissell, 2000; Wynhoff et al., 2011). They are considered as being especially favorable for both common and endangered butterflies (Munguira and Thomas, 1992; Ries et al., 2001; Saarinen et al., 2005). However, if the road mortality is high, then the conservation value of the respective road verges would be diminished. Road networks and traffic volumes are increasing across the globe (Forman and Alexander, 1998; Selva et al., 2011) and thus the esti- mation of road mortality and establishment of which factors affect the number of roadkills is an essential issue as regards the conser- vation of insects living on road verges and in semi-natural habitats in the vicinity of roads. Surprisingly, there are only a few estima- tions of the number of roadkills and the factors determining them (Munguira and Thomas, 1992; Ries et al., 2001). On a larger spatial scale, it has been shown that butterflies are one of the most common insect groups being killed on roads (Mckenna et al., 2001; Rao and Girish, 2007). 0006-3207/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biocon.2012.12.028 ⇑ Corresponding author. Tel.: +48 888151674. E-mail address: skorasp@poczta.onet.pl (P. Skórka). Biological Conservation 159 (2013) 148–157 Contents lists available at SciVerse ScienceDirect Biological Conservation journal homepage: www.elsevier.com/locate/biocon