UH Researchers are pioneers in exploring the sensory realm of these cold weather creatures
In the quiet of the empty Arctic, sounds that a city would mask, such as the barking of distant seals or the sound of water and wind, have great importance for polar bears. These sounds likely play a crucial role in helping them survive their harsh environment. However until recently scientists knew nothing about what polar bears could actually hear. Then, in the fall of 2005, Paul Nachtigall, of the Hawai‘i Institute of Marine Biology (HIMB) at the University of Hawai‘i, along with his colleagues Alexander Supin, from the Russian Academy of Sciences, and Mats Amundin, from Kolmården Zoo, gave the first polar bear hearing tests in history. With Nachtigall were UH graduate students Michelle Yuen, Aran Mooney and Kristen Taylor.
The tests were given at the zoo in Kolmården, Sweden. There three sedated polar bears were undergoing physicals before relocation to a zoo in Denmark. To test the bears, Nachtigall attached two gold electrodes to each animal’s head with small suction cups. He then used a special computer program stored in a laptop to generate sounds of varying frequencies. The electrodes captured the brain activity of the bears as they heard and mentally reacted to the sounds. “If you play a quiet sound, you get a small brain wave pattern, and if you play a loud sound, you get a big brain wave pattern,” says Nachtigall.
The tests were given at the zoo in Kolmården, Sweden. There, three sedated polar bears were undergoing physicals before relocation to a zoo in Denmark. To test the bears, Nachtigall attached two gold electrodes to each animal’s head. He then used a special computer program stored in a laptop to generate sounds of varying frequencies. The electrodes captured the brain activity of the bears as they heard and mentally reacted to the sounds. “If you play a quiet sound, you get a small brain-wave pattern, and if you play a loud sound, you get a big brain-wave pattern,” says Nachtigall.
The results of the tests surprised him. Polar bears themselves tend to generate low-frequency sounds. Their prey, likewise, generate low frequency sounds. The tests revealed that polar bears actually hear both low-frequency and extremely highfrequency sounds with equal acuity. “We think it’s because the ability to hear high-frequency sounds is really good for localizing sounds, such as movement by potential prey or ice cracking,” says Nachtigall, who has been investigating animal hearing capabilities and echolocation in marine mammals for 30 years.
To date, most of his studies have focused on dolphins. Nachtigall’s bear research has been the first attempt to test these animals’ hearing capabilities. New equipment Nachtigall and his UH research team have developed, in conjunction with Supin, a marine mammal physiology expert, allows quick and easy hearing tests on most mammals. A testing kit consists of a laptop computer, suction cups, a handful of gold electrodes, and amplifiers constructed with off-the-shelf materials available at most electronics stores. The total cost of building a kit runs less than $4,000.
The laptop holds unique software UH researchers are pioneers in exploring the sensory realm of these cold-weather creatures specifically designed to capture how an animal’s brain responds to rapid bursts of sound at varying volumes and frequencies. Nachtigall has relied on the computer programming skills of UH doctoral student Stuart Ibsen and the hardware design skills of UH doctoral students Taylor and Mooney to shrink the testing equipment to one-tenth its original size. As a result of the software improvements and faster computers, Nachtigall’s team has been able to reduce from months to hours the time required to convert hearing data from raw brain-wave measurements into usable research. The compact equipment size and speedy data recovery also allow Nachtigall and his colleagues to perform tests in a wider variety of settings, and with far less preparation time. “If you want to know what an animal hears, you can attach these electrodes, play some sounds, and have good data quickly,” says Nachtigall.
In the future, this equipment could be used to create baseline safe-noise thresholds for marine mammals and other animals. “If you go to a rock concert, you’ll lose your hearing but it will come back. You can look for where an animal just starts to lose its hearing a little bit and then it comes back, something called threshold shift,” says Nachtigall. This information could allow scientists to learn how much is too much sound for dolphins, whales, polar bears, and many other animals, and help mankind mitigate its aural impact on the animal kingdom.
Paul Nachtigall received his Ph.D. in comparative psychology from the University of Hawai‘i. He is currently the director of the Marine Mammal Research Program at HIMB, and is a former president of the Society for Marine Mammology. His research into cetacean hearing capabilities and physiology has played a key role in the development of advanced passive sonar systems.
Photo: Paul Nachtigall