Abstract 1| Road effect zone for bats not caused by lack of insects

The effects of roads and traffic can be detected for hundreds of metres from the road. Known as the road effect zone, this phenomenon effectively reduces the quality of habitat along roads, resulting in significantly larger impacts than is typically considered by road agencies.

The road effect zone can be caused by a number of different factors and identifying which one is essential to develop effective mitigation strategies. Wildlife may respond to the primary impacts of the road such as traffic disturbance, habitat loss or the gap in the canopy, or to a secondary impact, such as prey availability. For example, insectivores may be less abundant where there are fewer insects, thus a road effect zone for insects may be correlated to a road effect zone in insectivores. However, few studies explore this relationship between predators, prey and the road effect zone.

In this study we quantify the road effect zone for insectivorous bats and nocturnal flying insects, their primary prey. We surveyed bat call activity and collected insect samples along eighteen wooded transects that were perpendicular to three major freeways in south-east Australia (the Calder, the Hume and the Goulburn Valley Highways).

We found that 9 out of 10 insectivorous bat species evaluated in this study showed reduced activity within the first 200 m of a major freeway compared to up to 2000 m away from the freeway. However, we found no change in insect biomass with distance from the freeway, with the exception of order Orthoptera, in which biomass increased with increasing distance from the freeway.

Therefore, we suggest that the road effect zone for insectivorous bats is likely due to degraded habitat quality close to the freeway, from traffic noise spill and unsuitable or lack of vegetation, rather than a reduction in prey availability.

Further exploration of the role of these factors on the presence of bats near freeways is important to mitigate the road effect zone for insectivorous bats.

Abstract 2 | Artificial night-time lighting influences the use of wildlife crossing structures by insectivorous bats in Southeast Australia

Barrier-to-movement impacts of roads on nocturnal species, such as bats, may be amplified by the presence of artificial night-time lighting. Wildlife crossing underpasses are often used to reduce road impacts, however the new design of installing lights in underpasses for human co-use may reduce underpass use by bats.

In this study, we introduced light to these structures to evaluate if the presence of light alters the activity within and above the structures. We monitored the level of activity of bats under and above underpass bridges and culverts along a major freeway in Victoria, Australia. When lights were introduced, bat activity was lower under the structures but higher above the structures. This suggests that bats actively avoided the lit passageway, even if that meant potentially accessing “unsafe” habitat such as a roadway. Light can have a significant impact on the behaviour and movement of insectivorous bats and where possible, lighting should be avoided around critical bat habitat and in crossing structures actively used by bats.

Bio | Manisha Bhardwaj

Manisha Bhardwaj has recently completed her PhD at the University of Melbourne, investigating the impact of roads on insectivorous bats. Her research focuses on investigating and mitigating the impacts of urbanization and urban processes on wildlife. She is about to begin a postdoc position in Sweden at Sveriges lantbruksuniversitet continuing her research of the impacts of roads and rails on wildlife.