Characterizing Chilean blue whale vocalizations with digital acoustic recording tags: A test of using tag accelerometers for caller identification

Vocal behavior of blue whales (Balaenoptera musculus) in the Gulf of Corcovado, Chile, was analyzed using digital acoustic recording tags (DTAGs). We report the occurrence of Southeast Pacific type 2 (SEP2) calls, which exhibit peak frequencies, durations, and timing consistent with previous reports. We also offer the first description of tonal downswept (D) calls for this population. Since being able to accurately assign vocalizations to individual whales is fundamental for studying communication and for estimating population densities from call rates, we further examine the feasibility of using DTAG accelerometers to identify low-frequency calls produced by tagged whales. We cross-correlated acoustic signals with simultaneous tri-axial accelerometer readings in order to analyze the phase match as well as the amplitude of accelerometer signals associated with low-frequency calls, which provides a reliable method of determining if a call is associated with a detectable acceleration. Our results suggest that vocalizations from nearby individuals are also capable of registering accelerations in the tagged whale’s DTAG record. We cross-correlate acceleration vectors between calls to explore the possibility of using signature acceleration patterns associated with sounds produced within the tagged whale as a new method of identifying which accelerometer-detectable calls originate from the tagged animal.