Caller identification and characterization of individual humpback whale acoustic behavior

Acoustic recording tags are biologging tools that provide fine scale data linking acoustic signaling with individual behavior; however, when an animal is in a group, it is challenging to tease apart calls of other conspecifics and identify which individuals produce each call. This, in turn, prohibits robust assessment of individual acoustic behavior including call rates and silent periods, call bout production within and between individuals, and caller location. To overcome this challenge, we simultaneously instrumented small groups of humpback whales on a western North Atlantic feeding ground with sound and movement recording tags. This simultaneous tagging approach enabled us to compare the relative amplitude of each call across individuals and infer caller identity though amplitude differences. Focusing on periods when the tagged animals were isolated from other conspecifics, we were able to assign caller ID for 97% of calls in this dataset. From these labeled calls, we found that humpback whale individual call rates are highly variable across individuals and groups (0-89 calls/h), with calls produced throughout the water column and in bouts with short inter-call intervals (ICI = 2.2 s). Most calls received a likely response from a conspecific within 100 s. These results are important for modelling signal detection range for passive acoustic monitoring and density estimation. Future studies can expand on these methods for caller identification and further investigate the nature of sequence production and counter-calling in humpback whale social calls. Finally, this approach can be helpful for understanding intra-group communication in social groups across other taxa.