Exploring Killer Whale Acoustics

Last week I had the pleasure of delivering the Tuesday lecture to the marine biology class at the University of Puget Sound. Every September Professor Joel Elliott brings his students up from Tacoma for an on-the-water field lab, but this was the first time I got to follow up with an in-class session. Although I got a bit carried away talking about the historically contingent ontology of our southern resident killer whales and its implications for field biology and conservation, we spent a fair bit of time looking at orca bioacoustics: the ways in which these animals use sound.

Perhaps the biggest highlight of any encounter with killer whales is the look on my passengers’ faces when they first hear the animals vocalizing. Both Glacier Spirit and Olympus are equipped with hydrophones — special microphones designed to work underwater — that allow us to eavesdrop on the whales as they swim nearby. Those parts of their whistles and squeaks detectable by our ears often sound otherworldy! Sometimes our speakers are overloaded by a veritable cacophony, and at others perhaps just one lonely query from a distant whale will reach out for contact with the rest of its pod. Click here to listen to one of my favorite recordings, visualized as a spectrogram [a special kind of graph used in acoustic analysis] in the image at left. When Professor Elliott’s class joined us last month we were fortunate to overhear three different matrilines (matriarchal family groups) maintaining acoustic contact as they traveled together up Boundary Pass into the Strait of Georgia.

Tuesday’s lecture was an opportunity for me to share some of the bioacoustic work I began a few years ago, when I was one of Professor Elliott’s students. Using research grants from the University of Puget Sound and the Phi Sigma biology honors society, I purchased a particularly fancy hydrophone from Joe at Cetacean Research Technology and deployed it from Glacier Spirit and Olympus during the whale watching season. In addition to the echolocation (sonar) clicks that killer whales use to find their way around and catch prey, the southern residents have a unique vocabulary of pulsed calls. Like many sounds, the energy in these calls isn’t usually concentrated in a single frequency band, but is often spread across a certain number of overtones or harmonics. In the spectrogram shown here, the harmonics show up as stacked, more-or-less horizontal, lines. In human speech, these harmonics (called “formants”) are manipulated to produce different vowel sounds. One of my interests is how and why energy is distributed in different ways among these harmonics in killer whale calls.

Before class was over we surfed over to the Salish Sea Hydrophone Network, a project spearheaded by my friend Scott Veirs, the founder of the marine science school Beam Reach. The hydrophone network is a collection of hydrophones around the San Juan Islands and Puget Sound that stream live over the internet. We pulled up the live stream from Lime Kiln Light, on the west side of San Juan Island, and after less than a minute of listening we could hear the distant calls of J pod swimming down Haro Strait even as we sat there in Tacoma! Using these hydrophones scientists like Scott hope to gain a better understanding of how killer whales use the inland waterways of Washington and B.C., both physically and acoustically. I encouraged Professor Elliott’s students to take on a Beam Reach externship in bioacoustics, something anyone with an internet connection can do from home.

Although there is never enough time in a single lecture to convey all that one intends, I hope that their live encounter — both on the water and in the classroom — with the acoustic world of killer whales left the Puget Sound marine biology class with a deeper appreciation of these complex and mysterious animals.

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