Monitoring the phenology of the wood frog breeding season using bioacoustic methods

Abstract

The breeding phenology of wood frogs (Lithobates sylvaticus) in subarctic ecosystems is closely tied to the weather conditions at the onset of spring. With climate change occurring at an accelerated rate at high latitudes, we expect changes in the timing of the onset of spring to impact the timing of wood frog breeding. Wood frogs in the subarctic emerge from hibernation just after the snow melts and ambient air temperatures increase, but local and regional drivers of breeding phenology are not well understood and are difficult to study due to the relative inaccessibility of the region. We deployed passive acoustic monitors at multiple sites from 2011 to 2017 to track the timing of wood frog breeding based on calling activity and determine how this activity relates to environmental conditions. We developed a semi-automated approach for detecting wood frog calls, including the manual removal of false positives, and show that these estimates of activity are closely related to the timing of snowmelt and ambient air temperature. Our results suggest that wood frog breeding phenology in subarctic and arctic ecosystems will likely change in response to warming conditions, and we conclude that passive acoustic monitoring paired with semi-automated detection of wood frog calling provides an accurate and efficient method for tracking changes in population-scale wood frog breeding in this challenging and rapidly changing ecosystem.

Keywords

• Passive acoustic monitoring
• Wood frog
• Breeding phenology
• Automated acoustic detection
• Spring phenology
• Arctic