Autonomous recording units (ARUs) have proven useful for detecting cryptic bird species such as the king rail (Rallus elegans), clapper rail (Rallus crepitans; Stiffler et al. 2018), yellow rail (Coturnicops novebaracensis; Sidie-Slettedahl et al. 2015), and Dupont’s lark (Chersophilus duponti; Pérez-Granados 2018). While ARUs have clear limitations, they are often regarded as a valuable yet underutilized tool for detecting vocalizing target species—and are typically tested under ideal conditions. In environments where traditional call-and-response surveys or point counts are difficult due to anthropogenic noise or limited access, ARUs offer an alternative approach. We deployed 39 ARUs during the 2025 breeding season along the California State Route 37 Corridor in Northern California to aid in the detection of two cryptic and state-protected species: the California Ridgway’s rail (Rallus obsoletus obsoletus) and the California black rail (Laterallus jamaicensis coturniculus). Paired with habitat assessments, ARU placements revealed the presence of both species in unexpected, challenging, and previously unsurveyed locations. Our findings support the use of ARUs as an effective method for detecting cryptic species in complex environments. We further discuss how integrating ARUs with protocol-level surveys can enhance both detection rates and survey efficiency for secretive marshbirds.