Crane Voice Detective: Dr. Bernhard Wessling
Who's Calling? Using Voiceprints to Identify Individual Cranes
The Discovery of Crane Voiceprints
Dr. Wessling is a scientist who lives near Hamburg, Germany. He is a chemist who became interested in cranes when his sons were young. Over the years, he observed Eurasian (Common) cranes. He found mysterious behaviors that he assumed were characteristic for a certain crane individual or pair. But how could he be sure it was really the crane he thought it was when cranes look so much alike? Dr. Wessling got the idea to record the cranes' vocal calls and then to analyze their voices with a computer. He hoped their voices could help him be sure of a crane's identity--and his hunch was right!
The computer helped turn each vocal recording into a sonogram—a picture of the call showing its "melody" over time. The "melody" consists of all the tones (e.g. frequencies) expressed by the birds at a certain time, over the whole frequency spectrum looked at. Just as the patterns of each person's fingerprints are uniquely their own, the sonograms provide a way to determine a so-called voiceprint or "acoustic fingerprint" that identifies individual cranes and crane pairs. Dr. Wessling calculates the sum of all the intensities over the whole recording time shown for specific frequencies. In other words, at which frequency a certain bird makes more or less intense calls. And he found out: "Every bird shows a certain individually characteristic frequency spectrum. This is that bird's unique 'acoustic fingerprint,' taken from its recorded vocal calls. Every pair and every bird has a characteristic voice, just as we humans each have our own characteristic voice by which people recognize us without seeing us." This is big news!
This amazing discovery did not come easily. Dr. Wessling's first challenge was convincing people who cared for these endangered birds to let him in the refuge. After all, others had previously tried and failed at recording crane calls. But Dr. Wessling was sure he could do it! He convinced top crane officials—including Tom Stehn—to let him work in the refuge for nine days with these endangered birds. Then another tough job began. Dr. Wessling told Journey North:
It is often not as easy as it sounds here! Some calls I can record in the morning. To do this, I am in the Refuge 1.5 hours before sunrise, in total darkness, to approach the roosting place. Then I wait. If I am lucky, the crane pairs express a morning call--a unison call. Sometimes two, three, or four crane pairs call, one after the other. (One crane pair might be a quarter or half mile away from me, and the next pair a mile away.)"
Then came the painstaking work of analyzing. "I had to erase all the bad noises and side noises in order to analyze them. Some recordings were hard to analyze as it was windy, or waves were making noise, or other birds were calling, or the ships in the Intracoastal Waterway roaring. All of these bad noises had to be erased."
A Little Help From His Friends
Success! We Hear You, and We Know Who You Are
What did all this work accomplish? From his 1999 study, Dr. Wessling reports: "From the 27 pairs, 22 gave a unison call, 17 a guard call, and 12 gave both. In order to get these analyzable calls, I made more than 200 recordings. I only failed to characterize two pairs, one of which was not present. " Dr. Wessling didn't visit the location of 23 or 24 pairs, so they remained to be recorded on another visit in 2001. After his 2001 visit to Aransas, Dr. Wessling reported: "This time, I was able to get at least 25, maybe 27 pairs to call at me. Four pairs are new for me. Together with some pairs recorded by Brian Johns in summer 2000 at Wood Buffalo National Park, we now "personally" know 35 whooping crane pairs—or more than 70% of all breeding pairs." Great news!
Just in Time
Voiceprints are a valuable discovery. Scientists stopped banding cranes in the late 1980s. Banding was expensive, time consuming, exhausting—and dangerous to the cranes. In around ten years, no more cranes with bands will be alive. (Some cranes can live over 20 years, although the average lifespan is eleven.) At this writing, only about 20 cranes with bands survive out of a total crane population of 177 (Feb. 2001 numbers). With so few left, monitoring the world's only remaining wild Whooping Cranes is ever more important to saving the species. But how can cranes be safely monitored? Thanks to Dr. Wessling's work, they can now be kept track of with acoustics, or sound, and the discovery that cranes' individual voices can tell us which crane is which.
Dr. Wessling's recording and analysis is also a sign of his attitude towards nature. He says,"I love, admire, and RESPECT nature and animals and plants. Recording is LISTENING, and listening is a form of respecting. The more I listen, the more I learn. The more I learn, the more I respect."
This! Discussion/Journaling Questions
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