Here’s Why the Ears of Barn Owls Are Ageless, Unlike Other Mammals
Even if a person has lived a rather dull, quiet life — no concerts, raucous parties, and other noisy activities — the individual’s sense of hearing will deteriorate to a certain extent over time. By age 65, most people will have lost more than 30 decibels in sensitivity at high frequencies due to age-related hearing deterioration known as presbycusis. The amount can be significantly more, depending on lifestyle and genetics, among other factors.
Barn owls, conversely, appear to experience no such age-related hearing loss. Their ears, according to new research published in the journal Proceedings of the Royal Society B, are ageless.
Co-author Christine Köppl of the University of Oldenburg’s animal physiology and behavior group told Seeker “an ageless ear is possible if the regenerative mechanisms can be kept going.”
That is what she and her colleagues observed in their test subjects: seven barn owls named Weiss, Grün, Rot, Lisa, Bart, Ugle, and Sova. The owls were all hatched in captivity and lived in aviaries.
The researchers divided the owls into two groups based on their respective ages. The owls in the young group were less than 2 years old, whereas the old owls were 13–17 years old. The scientists then tested each owl on its ability to hear frequencies of 0.5, 1, 2, 4, 6.3, 10, and 12 kilohertz.
The scientists trained the owls to travel from one perch to another whenever the birds heard a tone, which lasted for just an instant. Upon successful completion of the tasks, the birds received tasty food rewards. To minimize training effects, the birds were tested separately and the sequence of the various frequencies was randomized for each owl.
In addition to comparing the hearing abilities of young versus old owls, the scientists also tracked the auditory sensitivity of Weiss during his impressive lifetime. This owl lived to be 23, well beyond the typical barn owl lifespan, which is just 4 years in the wild.
All of the tests demonstrated that the owls’ hearing sensitivity was not affected by age. The findings are consistent with prior research that found birds, fish, and amphibians have the capacity to regenerate lost “hair” cells in their hearing sensory organ known as the basilar papilla. The hairs are actually long, flexible organelles that help to convert sound vibrations into electrical signals that travel to the brain along the auditory nerve.
“The regeneration mechanisms, and therefore their benefits, are likely present in all bird species,” senior author Ulrike Langemann told Seeker. “The amazing thing is that the majority of small bird species are rather short-lived, and thus will never really benefit from a preservation of auditory sensitivity at old age.”
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 lossoccurs 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.”
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.”
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.”