Talk Effects of low and medium traffic roads on bat activity and species richness

The adverse effects of roads on bats are a recent and still poorly documented issue. Most of the research focuses on characterizing locations of bat collisions and the factors driving them or describe the negative effect of large and high traffic highways on bat activity and diversity. Low to medium traffic roads are often assumed to have negligible impact on many vertebrates, including bats.

To our knowledge no study has focused on the effects of low and medium traffic roads on the activity of different bat guilds defined on the basis of their echolocation range.



We examined the effects of distance to low and medium traffic roads on flight activity, species richness and three bat guilds (short-, mid- and long-range echolocators). We used acoustic recorders to survey bat activity in open agricultural and forest areas along perpendicular transects to low and medium traffic roads, applying a newly developed automatic classifier to identify bat calls.

We tested the hypothesis that proximity to roads decreases bat activity and diversity and that this effect is more pronounced in open areas where the sparse shrub and tree cover have a low capacity to buffer road induced disturbance. We expected bats with short-range echolocation to be particularly sensitive to road disturbance because traffic noise reduces their foraging efficiency.


The study was done in spring and summer of 2015 in southern Portugal.  We surveyed twice (in May and August) 20 transects perpendicular to three national roads. At each transect bat activity was registered simultaneously at 0, 50, 100, 200, 500 and 1000 m from the road with a automatic bat ultrasound recorder. Bat surveys were carried out in the two main land uses at the study site: dense Mediterranean woodland (“montado”) and open agricultural areas (cereal crops and pastures). The effect of distance to road, road type and land use on bat activity and ensemble composition were analysed with generalized estimating equations.


Overall bat activity and bat species richness increased with increasing distance from the roads for all the road types tested. Bat activity close to roads was approximately one-half the activity level recorded at 1000m. This effect is less noticeable in mid summer hot nights, corresponding to peak activity and first flight of juveniles. We found forest areas as positively affecting bat richness across all distances to roads. The activity of short and mid-range echolocating bats is particularly affected by the proximity to roads. This effect is stronger in forest areas and, surprisingly, near low-traffic roads. Large-range echolocators were unaffected by the presence of roads or landscape characteristics.


This study highlights the negative effects of low traffic roads on bat activity and diversity. We also show that not all bats species are affected in the same way and that species that depend more on hearing are particularly prone to activity reductions near the roads. Implications for road management aiming to reduce its impacts on bats are discussed.

barrier effect, bats foraging activity, road effect distance, low-traffic roads, high-quality habitats