Northern Red-Legged Frog Use of a New Under-Road Crossing and Adjacent Upland Habitat

A population of northern red-legged frogs (Rana aurora) located in northwest Portland must make a perilous crossing over U.S. Hwy 30 to access their breeding habitat in the floodplain of the Willamette River. To address the significant frog mortality that has historically resulted from this seasonal crossing, the Oregon Department of Fish and Wildlife managed the installation of an under-road crossing structure, completed in October 2024. To date, no studies have documented the effectiveness of crossing structures installed for R. aurora use, and few studies have examined their effectiveness for amphibians after installation. To meet these needs, our research will determine the efficacy of the structure for facilitating the migration of red-legged frogs between their lowland and upland habitats by combining the use of passive camera monitoring, PIT tagging, radio tracking and upland habitat analysis, in collaboration with partners at Oregon Metro, ODFW and USGS. Our study aims to investigate structure use as a mechanism for improved habitat connectivity for R. aurora and other species, a key issue for wildlife managers identified in the Oregon Conservation Strategy (OCS), while simultaneously informing management for an OCS species. This presentation will outline our study objectives, predictions and hypotheses, describe ongoing field methods, and share our preliminary findings from the first frog migration following structure installation, with the goal of generating valuable discussion about amphibian movement and habitat connectivity in urban ecosystems.