How many rodents die on the road? Biological and methodological implications from a small mammals’ roadkill assessment on a Spanish motorway

Abstract

Some small mammal species use road verges as a habitat for sheltering. As a result, their populations suffer mortality from roadkill in an unknown extent. We analysed the road mortality of small mammals and the population impact of roadkill on wood mouse along 1 year on a 4‐km motorway stretch. To account for potential bias in carcass sampling, we conducted walking surveys with the traffic interrupted and we performed three carcass persistence experiments to estimate total number of roadkills. The estimations were contrasted with previous studies and the population abundance on the road verges. The spatial pattern and the effects of seasonality and traffic volume on roadkill were analysed. We recorded 84 rodent carcasses with a mean carcass persistence of 6.65 days (SE = 0.41). The estimations of roadkill ranged between 190.2 and 238.3 individuals km−1 year−1, with a mean value close to a monthly 6 % mortality for the most common specie. Roadkill was more frequent during the hottest and driest months, and showed a unimodal relation with traffic peaking at 8100 vehicles day−1. A spatial aggregation of roadkill was detected with 80–190 m clustering. Our results suggest that, although rodents suffer greater roadkill mortality than previously reported, it affects a small percentage of the wood mouse population in our study area. This source of mortality is unlikely to affect population viability in the short term. Our results show that roadkill surveys should be specifically designed for small mammals to have a more accurate analysis of the effects of roadkill on their populations.

Disentangle the Causes of the Road Barrier Effect in Small Mammals through Genetic Patterns

“…Wood mouse population dynamics is also complex with, for instance, seasonal and annual population fluctuations due to density-dependent factors and food availability [ 113 , 137 , 138 , 140 ]. Although we believe that our simulation could capture the main population dynamics and replicate the genetic patterns among wood mouse populations separated by barriers of varying permeability, future work should aim to develop more complex models that more realistically incorporate the biology and ecology of the species, including the occurrence of road mortality [ 99 , 141 , 142 ].…”

“…This study provides evidence for the presence of a highway barrier effect in the wood mouse apparently due to road avoidance. This is likely an expression of behavioral avoidance of open areas [ 5 , 6 , 16 , 101 ] and not as a result of an inhibition to cross paved roads, as both attempted and successful paved road crossings have been recorded [ 39 , 40 , 99 , 141 ]. A road barrier effect due to road clearance avoidance is likely to occur in other small forest mammals [ 6 , 16 , 17 , 145 ].…”

Using road patrol data to identify factors associated with carnivore roadkill counts

“…While it is possible to modify driver behaviour, our data suggest that the anthropogenic variables included in our models may not be as significant as the various environmental variables in affecting serval roadkill rates on the N3. Removal of roadside vegetation that supports abundant rodent species (Ruiz-Capillas, Mata & Malo, 2015) could reduce the rate of serval roadkill, although this could impact plant and small mammal conservation. Keeping grass verges trimmed rather than removing vegetation entirely may be effective in manipulating the landscape of fear (Jacob & Brown, 2000) causing wildlife to spend less time in verge habitats without altering their abundance.…”

Using road patrol data to identify factors associated with carnivore roadkill counts

“…Our data, however, suggests that anthropogenic variables such as traffic speed limits may not be an important predictor of serval roadkill rates on the N3, so these measures may be less effective in this situation. Removing roadside vegetation may also reduce the rate of serval and owl roadkill, as this could reduce the abundance of rodent prey species (Ruiz-Capillas, Mata & Malo, 2015), although this could impact the conservation of other species such as plants and small mammals. Keeping grass verges trimmed, rather than removing vegetation entirely, may also be effective, by manipulating the landscape of fear (Jacob & Brown, 2000) and causing wildlife to spend less time in verge habitats without altering their abundance.…”