Use infrastructure to reduce vehicle collision risk along roads
Overall effectiveness category Awaiting assessment
Number of studies: 1
Background information and definitions
Collisions with vehicles on roads represent a serious mortality risk for butterflies and moths, especially for low-flying species which rarely go above the height of standard cars. For example, between 1 and 11% of 95 road crossings by Oregon silverspot Speyeria zerene hippolyta resulted in mortality (Zielin et al. 2016). Artificial structures may be used to try to encourage butterflies and moths to fly higher before crossing the road, therefore reducing the chances of collisions with vehicles.
Zielin S.B., Littlejohn J., de Rivera C.E., Smith W.P. & Jacobson S.L. (2016) Ecological investigations to select mitigation options to reduce vehicle-caused mortality of a threatened butterfly. Journal of Insect Conservation, 20, 845–854.
Supporting evidence from individual studies
A controlled study in 2012 on a disused road in Oregon, USA (Zielin et al. 2016) reported that “altitude guide” netting, and poles topped with bright colours or flowers, did not alter the behaviour of Oregon silverspot Speyeria zerene hippolyta butterflies. Results were not tested for statistical significance. Of 54 Oregon silverspots which encountered a net erected next to a road, only 10 flew over it, compared to 29 which flew around it, two which walked through it, and 13 which turned around. Of the 39 butterflies which flew over or around the net, 10 subsequently landed on the road. When the net was not present, 35 out of 60 butterflies flew between the net poles, nine turned around, and only four butterflies landed on the road. In a second experiment, of 41 Oregon silverspot that flew within one metre of poles topped with bright colours or flowers (attractive features), none ascended to the top. In 2012, a decommissioned road was divided into ten 8 × 7 m2 sections, spanning the 4-m-wide road and 2 m either side. Six trials, consisting of four 15-minute observation periods, were conducted on different sections. For two periods/trial, a 3-m-tall, 2-cm mesh net was stretched between two pairs of poles (7 m apart) on each side of the road, and for the other two periods the nets were absent. No further details provided. On 25 August and 1 September 2012, seven 1-m-high poles topped with attractive features: a bright colour (red: 3 poles, yellow: 2 poles) or flowers (2 poles), were observed for a total of 90 minutes. No further details provided.Study and other actions tested