For researchers studying the acoustic behavior of whales, distinguishing which animal is vocalizing is like a teacher trying to figure out which student responded first when the entire class is calling out the answer. This is because many techniques used to capture audio record a large sample size of sounds.
A major example of this is passive acoustic monitoring (PAM), which records audio via a microphone in one location, usually a stationary or moving platform in the ocean. While this method allows researchers to gather acoustic data over a long period, it is difficult to extrapolate fine-scale information like which animal is producing which call because the incoming audio signals could be from any number of animals within range.
Over the last 20 years, the invention of acoustic tags equipped with movement and audio sensors, which are suctioned harmlessly to the animal being studied, has tremendously improved data collection capabilities. Researchers in Syracuse University鈥檚 , led by , professor of biology, have been utilizing this technology to study the behavior of humpback whales in the North Atlantic Ocean.
In a recent study published in by Julia Zeh, a Ph.D. student in biology, along with other members of Parks鈥 lab and collaborators from the National Oceanic and Atmospheric Administration, the Center for Coastal Studies and UC Santa Cruz, researchers tagged many whales from the same pod simultaneously to analyze the vocalization of all members in the group. The goal was to uncover new information about whale behavior and communication 鈥 insights that are crucial for informing future conservation efforts.
鈥淏y simultaneously tagging all whales in a group, we were able to compare how loudly calls were recorded across tags to infer who was calling,鈥 says Zeh. 鈥淭his in turn lets us look at individual and group-level communication in ways that we couldn鈥檛 before.鈥
The team analyzed nearly 50 hours of synchronous tag data, including 16 tags from seven distinct groups of whales. Sound and movement data were collected from humpback whales in the Gulf of Maine near Stellwagen Bank National Marine Sanctuary in the western North Atlantic.
While the function and meaning of specific humpback whale calls remains largely unknown, researchers hypothesize that the calls might be associated with feeding or other social coordination. The team鈥檚 simultaneous tagging method allows researchers to analyze acoustic data about individual whales and compare that in the context of the larger group.
鈥淭his information can give us insight into how whales coordinate behaviors, how their calls relate to what they鈥檙e doing, what types of calls they use and what information they might exchange in group communication,鈥 says Zeh. 鈥淯nderstanding acoustic sequences within and between individuals also gives us insight into the complexity of the humpback whale communication system.鈥
If researchers know who is calling, they can associate vocal behavior with individual age, sex or the behavioral context of the calls. This data can also be used to enhance PAM studies, which are commonly used for species鈥 presence/absence verification and population counts.
鈥淗aving information from tag data about call rates and timing can improve count estimates,鈥 says Zeh. 鈥淔or example, having 10 calls doesn鈥檛 necessarily mean there are 10 whales, but potentially two whales calling back and forth, or one whale producing sequential calls.鈥
While previous studies have linked caller identity to acoustic tag data, this is the first robust method for studying large baleen whales, like humpback whales. The team’s efforts to enhance caller identification through simultaneous tagging provide a new resource for researchers to better understand animal behavior and advance wildlife conservation efforts.
The team鈥檚 work was supported by the Stellwagen Bank National Marine Sanctuary, the Office of National Marine Sanctuaries, the National Oceanographic Partnership Program, the National Defense Science and Engineering Graduate Program, the Office of Naval Research, the ACCURATE Project, the Cetacean Caller-ID project and the U.S. Navy Living Marine Resources Program.
