Factors affecting road mortality and the suitability of road verges for butterflies

Abstract

a b s t r a c tLittle 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 abundance 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 landscape. 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 butterflies 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.

Motorway as a barrier to dispersal of the threatened dragonfly Sympetrum depressiusculum (Odonata: Libellulidae): Consequence of mortality or crossing avoidance?

“…Munguira & Thomas, 1992;Yamada et al, 2010;Skórka et al, 2013;Baxter-Gilbert et al, 2015). Some have even focused on dragonfl ies (e.g.…”

“…In the case of butterfl ies, for example, mortality is positively correlated with road width, because an individual spends more time above the road surface in the case of a wider road, which increases the probability of it colliding with passing vehicles. It is not surprising, therefore, that small species are more likely to be killed when crossing roads (Skórka et al, 2013). Moreover, mortality is positively correlated with traffi c volume and speed (Forman & Alexander, 1998;Soluk et al, 2011).…”

Abundance of red-listed species in infrastructure habitats – ”responsibility species” as a priority-setting tool for transportation agencies´ conservation action

“…Amphibians and reptiles as well as mid-sized and large mammals can experience high levels of traffic mortality (Fahrig and Rytwiski 2009), and accordingly we have not included vertebrates in our study. Concerning insects however, available research suggests that traffic mortality rarely has effect on the population level (Munguira and Thomas 1992, Hopwood 2008, but see Weidemann and Reich 1995, and that the benefits from infrastructure habitats outweigh the hazard from passing vehicles (Thomas et al 2002, Hopwood 2013, Skorka et al 2013), but the matter deserves further study. We suggest that the hazard will be minimized by directing habitat improvement or creation to low traffic infrastructure, or to the parts of the infrastructure corridor that is most distant from the traffic.…”

Railway tracks can have great value for butterflies as a new alternative habitat

“…Another threat for butterflies inhabiting railway tracks is road mortality (cf. Melis et al 2010;Skórka et al 2013). However, the traffic intensity on domestic railway tracks is lower than that on roads; therefore, this factor appears to have less importance.…”