Using Passive Camera Monitoring to Investigate Northern Red-legged Frog Use of a New Road Undercrossing Structure
Start Date
3-16-2026 10:00 AM
End Date
3-16-2026 10:09 AM
Abstract
Northern Red-legged Frogs (Rana aurora) make seasonal movements between lentic waters and adjacent upland forests to meet their life history requirements. This movement behavior makes the species particularly vulnerable to landscape fragmentation by roads, where traffic can cause large mortality events during the breeding period. To mitigate R. aurora mortality on U.S. Route 30 near Burlington, Oregon, an under-road wildlife crossing structure was installed by the Oregon Department of Fish and Wildlife and other partners in late 2024, reconnecting a forested public recreation area with protected wetland habitat in the floodplain of the Willamette River.
We used two specialized optical sensor cameras to monitor the crossing structure for amphibian and other wildlife activity from December 2024 through December 2025. Northern Red-legged Frogs were detected inside the structure more than 300 times from December to April, with use by adult males and gravid females. Juvenile R. aurora used the structure during the summer, likely dispersing from their natal wetlands below the road. We summarize use of the crossing structure by Northern Red-legged Frogs over one year of passive camera monitoring, with attention to documented complete passage by individuals. We also examine relationships between frog detections and several environmental covariates, including ambient temperature, humidity, and precipitation, to determine conditions that best predict movements by different age classes of frogs. Our findings can inform the design of future amphibian-focused road crossing structures in western Oregon and provide recommendations for effective passive monitoring of amphibians in these structures.
Subjects
Conservation biology, Transportation, Wildlife biology
Creative Commons License
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Using Passive Camera Monitoring to Investigate Northern Red-legged Frog Use of a New Road Undercrossing Structure
Northern Red-legged Frogs (Rana aurora) make seasonal movements between lentic waters and adjacent upland forests to meet their life history requirements. This movement behavior makes the species particularly vulnerable to landscape fragmentation by roads, where traffic can cause large mortality events during the breeding period. To mitigate R. aurora mortality on U.S. Route 30 near Burlington, Oregon, an under-road wildlife crossing structure was installed by the Oregon Department of Fish and Wildlife and other partners in late 2024, reconnecting a forested public recreation area with protected wetland habitat in the floodplain of the Willamette River.
We used two specialized optical sensor cameras to monitor the crossing structure for amphibian and other wildlife activity from December 2024 through December 2025. Northern Red-legged Frogs were detected inside the structure more than 300 times from December to April, with use by adult males and gravid females. Juvenile R. aurora used the structure during the summer, likely dispersing from their natal wetlands below the road. We summarize use of the crossing structure by Northern Red-legged Frogs over one year of passive camera monitoring, with attention to documented complete passage by individuals. We also examine relationships between frog detections and several environmental covariates, including ambient temperature, humidity, and precipitation, to determine conditions that best predict movements by different age classes of frogs. Our findings can inform the design of future amphibian-focused road crossing structures in western Oregon and provide recommendations for effective passive monitoring of amphibians in these structures.