Calculating Underwater Auditory Thresholds in the Freshwater Turtle Trachemys scripta elegans

Knowledge of an animal’s hearing sensitivity is critical to understanding how species perceive their auditory world and their susceptibility to hearing loss when exposed to anthropogenic noise. Auditory evoked potentials (AEPs) are commonly used to measure auditory responses, but it can be challenging to compare thresholds across studies. A tractable source of inter-study variation is the effect of the threshold determination method. Using control data collected for a study investigating underwater hearing loss in the freshwater turtle Trachemys scripta elegans (red-eared slider; n = 3), a subset of 400 Hz underwater thresholds was analyzed using three methods: regression, visual, and F-statistic. The regression method consistently calculated lower thresholds compared to the visual and F-statistic methods, with a mean difference of 6.2 and 7.3 dB re 1 μPa, respectively. The mean difference between the visual and F-statistic methods was 1.1 dB, with the F-statistic method producing the highest thresholds. Regression-determined thresholds were also lower than visual at 175, 600, 800, and 1000 Hz by a mean of 4.3–8.2 dB; relative sensitivity across frequencies was consistent between the two methods. Elucidating how thresholds may vary depending on analytical approach improves our ability to compare data across Testudine species, a highly threatened taxon.