Mammals, including humans, have only a limited capacity to regenerate these hair cells when they are lost not only by aging, but also by injury or disease. According to the National Institutes of Health, more than 90 percent of hearing loss occurs when either hair cells or auditory nerve cells are destroyed.
Langemann and colleagues believe that at some point in mammal evolution, the ability to fully regenerate hair cells was lost.
“The current view is that, unfortunately, the genetic switch for the inner ear of mammals is in the off mode,” Köppl explained.
For barn owls, it appears that natural selection highly favored retention of their hair cell regeneration mechanisms. Lead author Bianca Krumm, also from the University of Oldenburg, said barn owls are predominantly nocturnal hunters with fairly large broods for a bird of their size. Most are between 13–15 inches in length. Females cannot leave their nests within the first five days of their chicks hatching because they must keep their otherwise unprotected offspring sufficiently warm.
“Male barn owls may thus face the job of catching about 30 to 40 mice per night for the family, independent of nocturnal lighting conditions,” Krumm said. “Thus ‘hunting by ear only’ must have been the solution. This includes sensitivity as well as amazing sound localization abilities. Indeed, scientists have shown that a tame barn owl will catch a prey item in complete darkness.”
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Aside from their ageless ears, barn owls possess superior hearing to that of humans due to the parabolic shape of the facial disc, the concave collection of feathers on the bird’s heart-shaped face that functions like a satellite dish.
“The parabolic effect of the barn owl’s facial disc improves the sensitivity roughly by a factor of 10 in intensity compared to our human auditory sensitivity,” Langemann said, adding that if tiny headphones are placed directly in the ears of barn owls, their hearing is reduced to that of other bird species.
Barn owl ears are entirely covered with feathers, which is thought to protect the ears and to help reduce air drag when the birds are in flight.
Co-author Georg Klump said the researchers are investigating how different pathologies affect aging mammalian inner ears. They are also hoping to learn more about how barn owls locate prey so accurately using their sense of hearing.
“We are biologists and firmly believe that animals can teach us amazing things,” he said. “Different animals may indicate solutions for some of the many problems related to our modern, but aging, society.”
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Since scientists cannot yet apply the regeneration mechanisms of birds to humans suffering from hearing loss, the researchers advise that everyone should take steps to safeguard their sense of hearing as much as possible.
“Listening to very loud music plays a role in hearing loss because it may damage sensory hair cells and the connecting nerve fibers immediately,” Langemann said. “However, the impact from constant and work-related noise is as serious. These are some of the reasons why wearing ear protection for specific types of work are nowadays standard in the professional world.”
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