Strategies to combat habitat fragmentation, such structures that help wildlife cross roads like over- and underpasses, may have to contend with more than just fragmentation.
Other anthropogenic pressures, like artificial light at night (ALAN), can act in concert with habitat fragmentation to affect how wildlife move through landscapes. What happens when the strategies meant to mitigate habitat fragmentation, like road underpasses, are met with another wildlife threat, like ALAN?
While the body of research on the effects of ALAN on wildlife is growing, most studies have focused on organisms such as small rodents and bats. Larger mammals, which typically have larger habitat requirements, may respond uniquely to the fragmentation of their habitats via ALAN.
Sordello, R., Ouédraogo, D.Y., Chassoulier, C., Aulagnier, S., Coulon, A. and Reyjol, Y. 2025. Does artificial light interfere with the activity of nocturnal mammals? An experimental study using road underpasses. Biological Conservation 302: 110960.
In a new study, researchers examined the effects of ALAN on larger mammals’ use of road underpasses. Over a three year period, they compared animal movements through five road underpasses in a natural park in France. They examined movements before, during, and after the installation of LED lights in the underpasses for one year per period. Using camera traps, they recorded the movement of 12 mammal species, focusing their analysis on the three most commonly recorded species: European badger, red fox, and martens.
Artificial light at night decreased the probability of using a road underpass for two of the three species, depending on the season. Additionally, badgers reduced their speed of crossing in the presence of artificial light. Although road underpasses may be in place to help animals avoid the effects of habitat fragmentation, ALAN may decrease their efficacy.
However, results from this study showed that the negative effects of ALAN are reversible. Within a year of lights being removed, the probability of the three mammals crossing was identical to pre-lighting periods.
Habitat fragmentation is rarely the only challenge facing ecosystems and wildlife. Although recent policy in the U.S. has been supportive of building structures to promote connectivity across roads and highways, anthropogenic changes such as ALAN can interact with connectivity structures to decrease their usefulness. When altering landscapes to improve connectivity, multiple threats to wildlife should be considered in order to maximize conservation benefits.
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