Loss of acoustic habitat due to anthropogenic noise is a key environmental stressor for vocal amphibian species, a taxonomic group that is experiencing global population declines. The Pacific chorus frog (Pseudacris regilla) is the most common vocal species of the Pacific Northwest and can occupy human‐dominated habitat types, including agricultural and urban wetlands. This species is exposed to anthropogenic noise, which can interfere with vocalizations during the breeding season. We hypothesized that Pacific chorus frogs would alter the spatial and temporal structure of their breeding vocalizations in response to road noise, a widespread anthropogenic stressor. We compared Pacific chorus frog call structure and ambient road noise levels along a gradient of road noise exposures in the Willamette Valley, Oregon, USA. We used both passive acoustic monitoring and directional recordings to determine source level (i.e., amplitude or volume), dominant frequency (i.e., pitch), call duration, and call rate of individual frogs and to quantify ambient road noise levels. Pacific chorus frogs were unable to change their vocalizations to compensate for road noise. A model of the active space and time (“spatiotemporal communication”) over which a Pacific chorus frog vocalization could be heard revealed that in high‐noise habitats, spatiotemporal communication was drastically reduced for an individual. This may have implications for the reproductive success of this species, which relies on specific call repertoires to portray relative fitness and attract mates. Using the acoustic call parameters defined by this study (frequency, source level, call rate, and call duration), we developed a simplified model of acoustic communication space–time for this species. This model can be used in combination with models that determine the insertion loss for various acoustic barriers to define the impact of anthropogenic noise on the radius of communication in threatened species. Additionally, this model can be applied to other vocal taxonomic groups provided the necessary acoustic parameters are determined, including the frequency parameters and perception thresholds. Reduction in acoustic habitat by anthropogenic noise may emerge as a compounding environmental stressor for an already sensitive taxonomic group.
Males of most anuran species use acoustic communication to attract females. Rana aurora (Northern Red-legged Frog) is one of a few anuran species that calls underwater, making it difficult to survey using traditional visual and auditory methods. R. aurora are experiencing significant population declines and are listed as a sensitive species in Oregon. Lack of information on basic life-history strategies may limit conservation efforts. This study explored calling behavior and breeding phenology of R. aurora by quantifying seasonal and diel calling patterns. An audio recorder with an underwater microphone (called a hydrophone) was used to capture underwater vocalizations at Finley National Wildlife Refuge near Corvallis, Oregon, USA. Results suggest that male R. aurora chorus from January until March for up to 14 h per day at a time. This is a significantly longer duration than previously recorded. This study shows that passive acoustic surveys can improve the detection and monitoring of a cryptic species, which allows for better monitoring and surveying of this species.
Fitness consequences of anthropogenic noise on organisms that have chorus-dependent breeding requirements, such as frogs, are not well understood. While frogs were thought to have innate and fixed call structure, species-specific vocal plasticity has been observed in populations experiencing high noise conditions. Adjustment to call structure, however, can have negative fitness implications in terms of energy expenditure and female choice. The Pacific chorus frog (Pseudacris regilla), a common vocal species broadly distributed throughout the Pacific Northwest, often breeds in waters impacted by road noise. We compared Pacific chorus frog call structure from breeding populations at 11 high- and low-traffic sites in the Willamette Valley, Oregon. We used passive acoustic monitoring and directional recordings to determine mean dominant frequency, amplitude, and call rate of breeding populations, individual frogs, and to quantify ambient road noise levels. Preliminary results indicate that while individuals do not differ in call rate or structure across noisy and quiet sites, high road noise levels decrease the effective communication distance of both the chorus and the individual. This research enhances our understanding of acoustic habitat in the Willamette Valley and the impacts of anthropogenic noise on a native amphibian species.
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