Past Projects

Effects of Duty Cycles on the Passive Acoustic Monitoring of Southern Resident Killer Whales (Orcinus orca).

Long-term passive acoustic monitoring (PAM) of cetaceans is essential to many studies of cetacean behavior, occurrence and ecology. However, passive acoustic recorders that are not connected to land stations are often limited in the amount of time they can operate due to limitations of storage space or battery life. Duty cycles help to facilitate long-term recordings in these situations, because they are a method of sub-sampling during the recording process where a recorder is only active for a specified amount of time on a repeating cycle (i.e. 5 min. every 30 min.). However, it is often assumed that duty cycled data provides a random sample of cetacean acoustic behavior, which is not necessarily the case.

A duty cycle records for a specific amount of time (listening proportion) on a repeating cycle that also has a specific length (cycle length). These two duty cycle characteristics vary widely throughout studies of cetaceans.

For this study, I investigated the impact that certain duty cycle characteristics have on the answers to specific questions about Southern Resident killer whale occurrence and behavior. Using continuous data, I created 288 possible sub-sampled datasets, answered the same questions of all the datasets and compared the answers with the continuous data using generalized linear and generalized linear mixed models.

Ultimately, I found that questions that require broad-scale acoustic information about SRKW can be answered accurately with all commonly used duty cycles. However, questions that need fine-scale acoustic information, require longer cycle lengths (>30 min) and longer listening proportions (0.5 or more). More broadly, the best duty cycle for the collection of fine-scale acoustic behavior depends on the behavior of the species of interest in the study area, therefore, preliminary studies using continuous data should be used to select the optimal duty cycle and to quantify the amount of uncertainty arising from using duty cycled data.

This work was completed with the support of Julie N Oswald and Jason Wood as part of my MSc at the University of St Andrews.

To learn more, see our publication in JASA: Rand ZR, Wood JD, Oswald JN. 2022. Effects of duty cycles on passive acoustic monitoring of Southern Resident killer whale (Orcinus orca) occurrence and behavior. The Journal of the Acoustical Society of America. 151(3):1651-1660.

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