Investigating the impacts of road noise on Pacific chorus frogs
This project focuses on the Pacific chorus frog, Pseudacris regilla. It is Oregon's most vocal native species, and it breeds in a wide array of habitats, including ponds and pools near roads. While it isn’t endangered, chronicling the effects of anthropogenic noise and specifically road noise on its calling structure may indicate acoustic habitat quality for other species as well as count as one of the few categorizations of the response of this genus to high noise levels.
Many species of frogs use male calling or chorusing as a way of attracting mates. For a long time, these calls were believed to be static; recently this has been shown to be otherwise. Frogs can change several aspects of their call structure, including (depending on the species) duration, calls per minute, and frequency, and they can do this in response to high levels of noise. Because frogs are less mobile than birds or bats, they may be more impacted by high levels of noise at breeding sites. Calling is energetically expensive for males, and changing calling may be more so. It may also create more difficulties for females trying to find the males to mate; they may not be able to orient toward males or choose the fittest specimens to mate with.
This research seeks to answer the question: how do high levels of road noise affect the calling behavior of Pacific chorus frogs? To examine this, two different ways of recording frogs and road noise are used. First, we deploy an array of 11 passive acoustic recorders (WildlifeAcoustics Songmeters) up and down the Willamette Valley from Baskett Slough in the North to Malpass Farms in the South. Half of these are in quiet sites, and the other half are right next to I-5. These record for several hours a day just after sunset to capture peak chorus times and noise levels from the nearby highway. Second, we go to each of the 11 sites with a high-quality directional microphone to record individual frogs for 5 minutes each. This allows us to look at frequency, duration, call rate, and source levels for individuals at a site. We also conduct a rapid demographic survey of males at each site to see if there are differences in populations between sites.