It’s been a long time coming, but the paper on evidence for multiple sound sources in the bottlenose dolphin appears in the October 15th issue of the Journal of Experimental Marine Biology and Ecology. I’ve been told that the PDF will be freely available soon, hopefully in the next week or so.
The abstract is:
Indirect evidence for multiple sonar signal generators in odontocetes exists within the published literature. To explore the long-standing controversy over the site of sonar signal generation, direct evidence was collected from three trained bottlenose dolphins (Tursiops truncatus) by simultaneously observing nasal tissue motion, internal nasal cavity pressure, and external acoustic pressure. High-speed video endoscopy revealed tissue motion within both sets of phonic lips, while two hydrophones measured acoustic pressure during biosonar target recognition. Small catheters measured air-pressure changes at various locations within the nasal passages and in the basicranial spaces. Video and acoustic records demonstrate that acoustic pulses can be generated along the phonic fissure by vibrating the phonic labia within each set of phonic lips. The left and right phonic lips are capable of operating independently or simultaneously. Air pressure in both bony nasal passages rose and fell synchronously, even if the activity patterns of the two phonic lips were different. Whistle production and increasing sound pressure levels are generally accompanied by increasing intranarial air pressure. One acoustic “click” occurred coincident with one oscillatory cycle of the phonic labia. Changes in the click repetition rate and cycles of the phonic labia were simultaneous, indicating that these events are coupled. Structural similarity in the nasal apparatus across the Odontoceti suggests that all extant toothed whales generate sonar signals using the phonic lips and similar biomechanical processes.
This was a big undertaking, requiring the coordinated effort of a lot of talented and busy people.
Diane Blackwood designed and implemented our acoustic recording layout and the dolphin stationing device and biteplate, and made sure the amplifying equipment was operational and protected from incident. (Incidents with electronics in proximity to sea water are all too common.) I designed and wrote the software that acted as a multichannel digital data recorder, the data reduction program, and the analysis program. Bill van Bonn was our veterinarian who spent our data recording sessions lying prone on the dock as he placed, checked, and positioned the endoscopes and pressure catheters. Our principal investigator, Ted Cranford, operated the video side of things, including the high-speed video capturing the endoscope views. Sam Ridgway and Don Carder consulted with us, helping us with the use of the pressure catheters (which had previously been used in two prior studies they authored). Monica Chaplin and Jennifer Jeffress were the dolphin trainers on the spot during data recording. Tricia Kamolnick and Mark Todd were trainers who helped get the subjects prepared for our data collection process, and Mark Todd implemented the regular video system. It took between two and three hours each data collection day for us to set up, test, and calibrate all the equipment. Breaking down took somewhat less time, but I would still have to run a custom program to demux the data, produce images visualizing the data for each trial, and then shift the day’s data off the hard disk and on to CD-ROM media.
Update: The Marine Mammal Center has put up the PDF of the paper.