Papers by Mireille Gravel
Amphibia-Reptilia, 2012
We investigated whether paved roads adjacent to 16 ponds acted as barriers to movements of juveni... more We investigated whether paved roads adjacent to 16 ponds acted as barriers to movements of juvenile wood frogs (Lithobates sylvaticus), green frogs (Lithobates clamitans), mole salamanders (Ambystoma laterale, A. maculatum), and American toads (Anaxyrus americanus) in eastern New Brunswick, Canada. Using pitfall traps and drift fences, we recorded captures of juveniles dispersing away from their natal ponds into forest habitat (pondside fences) or across the road (roadside fences) over two field seasons. To explain variations in abundance of dispersers among sites, we measured several road-associated variables including traffic intensity and roadside habitat structure, pond quality, and weather variables. We estimated the activity patterns (across 4-day periods) and seasonal abundance of juveniles in transit between ponds and terrestrial habitat using generalized linear mixed models. For all groups, activity across 4-day periods increased with either total precipitation or minimum air temperature. However, road-associated variables were also important for some species. Mole salamander activity was lowest next to roads. Wood frog activity increased with minimum air temperature, but the effect was weakest at roadside fences (minimum air temperature × fence position interaction). Seasonal abundance of most groups varied with habitat structure or pond hydroperiod. Green frog abundance decreased with increasing traffic intensity, but abundance was higher at roadside fences than pondside fences. In contrast, wood frog seasonal abundance tended to be lowest at roadside fences. We conclude that road-associated disturbances are detectable at fine temporal scales and that amphibian responses to such variables can be influenced by weather variables.
Herpetologica, 2005
Nocturnal car traffic often results in amphibian casualties, especially during rainy nights. The ... more Nocturnal car traffic often results in amphibian casualties, especially during rainy nights. The behavior of amphibians presumably influences their vulnerability to mortality on the road, but this hypothesis remains untested. We investigated the behavioral response of individuals of six species of amphibians on roads when confronted by an approaching vehicle. We first conducted a field study consisting of 50 night-driving surveys over 4 yr during which we recorded the behavior (i.e., moving or immobile) of frogs, toads, tree frogs, and salamanders encountered on a 20-km stretch of road. In an effort to tease apart the effects of headlights and the sound of motors on amphibian behavior, we carried out a field experiment on a test road where we exposed individuals to different car-associated stimuli. Here, we tested the hypothesis that simultaneous exposure to headlights and the sound of a car motor would elicit a stronger response than exposure to a single stimulus or a control. Based on the observations of the 2767 individuals in the field survey, immobility was the most common response to the approach of a car (mean probability of 0.82 of remaining immobile); the response differed across species but depended on the season of the survey (May-June vs. July-September). Similarly, the 91 individuals included in the field experiment were more likely to move during the control treatment than during any of the car-associated treatments. The combined stimuli elicited the strongest response, followed by the headlights-only and the motor-only treatments. Spring peepers (Pseudacris crucifer) tended to move more often than the other species we tested in the field experiment, which suggests they spend less time on the road and are less vulnerable to traffic mortality than other species. Both the field survey and field experiment consistently indicated that amphibians tend to remain immobile at the approach of a vehicle. This behavior highlights the vulnerability of amphibians to road traffic and should be considered in measures to mitigate road impacts.
Uploads
Papers by Mireille Gravel