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Crane Voice Detective: Dr. Bernhard Wessling

Who's Calling? Using Voiceprints to Identify Individual Cranes

The Discovery of Crane Voiceprints
Dr. Wessling
If you're a whiz at recognizing someone's voice when they call on the phone, it's because humans each have a voice all their own. You might be surprised to learn that many of the world's endangered whooping cranes can also be identified by their voices!

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!

One-of-a-Kind
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!

Hurdles
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:

Photo
Steve Hillebrand
"As a researcher who is officially entitled to record Whooping Crane calls for conservation reasons, I am allowed to enter into closed areas. I access the cranes by walking through grasslands, wetlands or wet marshes, trying to avoid being seen by them. When I am close enough to a pair, I play a CD recording from an original Whooping Crane call using a loud megaphone. The pair in front of me hears it and thinks: "Oh, another Whooping Crane is intruding in our territory! Let's tell them that this is our territory." Then they call, and I record.

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
Brian Johns (left) and Tom Stehn record Whooping Crane calls.
After his first session at Aransas, Dr. Wessling sent his special recording equipment to Brian Johns at Wood Buffalo National Park where the wild Whooping Cranes nest. Brian entered the grounds by helicopter and called to the birds with Dr. Wessling's recordings on a CD played over a megaphone. Brian recorded the Wood Buffalo cranes' answers for Dr. Wessling to analyze. And Dr. Wessling returned to Aransas in January 2001 to record the cranes again on their wintering grounds. His goal was to get more recordings of already-recorded cranes and also the pairs he missed in 2000.

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 tests his recordings in the Ultralight Plane
Dr. Wessling's recorded crane calls play a big role in the success of the work conducted by Operation Migration to help endangered Whooping Cranes. A trial of the bold migration project took place in fall 2000 with non-endangered Sandhill Cranes before it could be tried with highly endangered Whooping Cranes. Dr. Wessling says, "This marked the first time we were talking to the cranes in crane language."

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."


Try This! Discussion/Journaling Questions
1. What is the significance of Dr. Wessling's work to the future status of endangered whooping cranes?

2. Why is the identification of cranes by their voices such a significant breakthrough?

3. Operation Migration will carry out ultralight-led migrations as a way of reintroducing a new flock of wild migratory Whooping Cranes to the Eastern part of North America, where the last natural flock vanished over a century ago. It will take several years to build up the flock until the ultralight planes and pilots are no longer necessary. Do you think such a project is important? Explain.

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