Digital Bioacoustics

I've got another study on owl hearing for those of you who have enjoyed some of my past articles. This one looks at the ability of birds to regrow the tiny hairs responsible for mechanoelectrical transduction of soundwaves to nerve impulses and its contribution to preventing age related hearing loss.

cross-posted from: https://lemmy.world/post/16024126

This summary is of "Barn owls have ageless ears," by Bianca Krumm, Georg Klump, Christine Köppl, and Ulrike Langemann (2017). This is my best interpretation of their study and findings. I'm not a scientist, just a hobbyist, so feel free to browse the source provided and correct me if I've gotten anything incorrect.

Time for another look at another amazing bit of owl research!

In this paper, the researchers looked into owls as creatures with amazing hearing, to see how their hearing changes with age. I will go over some of their testing and findings to try to break down what they did and what was learned. As always, this is not my area of expertise, so if you do understand this well and are curious, please take a look at the full paper and fill me in on what I misunderstood.

The National Council on Aging says that 1/3 of people ages 65-74 and 1/2 of those 75 and older suffer from hearing loss. Mammals as a whole suffer from presbycusis, age related hearing loss due to changes in the inner ear structures. Birds, while having different, but functionally similar ear structures, do not seem to suffer from these effects.

Mammalian presbycusis is associated with progressive damage to the loss of hair cells inside the corti, an organ of the cochlea, the spiral shaped part of your inner ear. This is a very small structure, so I’ve included a picture of the cochlea, a picture of the tiny hairs we’ll be discussing, and a 3D printed cochlea to give a size perspective. I then also have a Barn Owl cochlea picture.

These tiny hairs are responsible for mechanoelectrical transduction of sound. That is a process that turns vibrational energy from sound waves into an electrical signal in the nerves of the cochlea which your brain can interpret as sound. Click this link for a brief article on mechanoelectrical transduction.

Humans and most mammals have partial regeneration of the hair cells of the inner ear, but they cannot replace these sound sensing hairs in the cochlea. Some other vertebrates, birds in particular, have been studied for some time as they can regenerate their basilar papillae, the structure in birds that serves the same purpose as the corti do in mammals.

Prior studies of the basilar papillae have shown amazing regenerative properties of the sensory hairs. Many species have been looked at showing a lack of age-related damage, and even in experiments where chemicals were applied directly to damage the hair cells experienced very quick recovery and growth of new hairs. As long as the hair growing cells themselves are not damaged, the hairs can grow back when damaged from age or by physical trauma.

Most hearing loss in mammals occurs at higher frequencies. Prior studies of their range of sounds they can hear had shown Barn Owls are able to hear sounds between 200 Hz – 12 kHz. The higher 12kHz is higher than most other birds can hear, so the Barn Owl became a great candidate species to study presbycusis. The Barn Owl’s has a specialized cochlea with one of the longest basilar papilla of any bird. Low frequency hearing appears to be similar to many other birds, but there were numerous differences to the inner ear to better process mid to high frequencies.

I was happy to learn we had names and backstories to our test subjects this time! They were all Common Barn Owls, Tyto alba, the most widespread owl in the world. The group of young owl, aged >2 years, consisted of Ugle, Sova, Grün, and Rot, and the old owls, aged 13 and 17, were Bart and Lisa, along with a third owl, Weiss. Most of them were hatched at German universities, but I’m thinking Bart and Lisa may have come from somewhere else, as I imagine this can only be a Simpsons reference as they were born in the 90s.

Experiments were conducted in two sound-deadened chambers. In the chambers, there was a starting perch and a target perch on the opposing side. A speaker was placed directly behind the target perch. There was a video camera to monitor the birds’ activity, and an automatic feeder near the target perch.

The owls were trained to sit on the starting perch facing the target. After a random time of 1-30 seconds, the owl was played a test signal over the speaker. Test frequencies of frequencies of 0.5, 1, 2, 4, 6.3, 8, 10, and 12 kHz were used. The owl knew a sound indicated a tasty snack was available and would fly over to get its reward. After the test signal was played, if the owl flew to the target immediately (within 5 or 10 seconds) it was taken as the owl had heard the auditory signal. In total, 99% of trials had a positive response occurring within 5 seconds upon hearing the test sound. “Catch trials” were done in 20-30% of all trials where no tone was played to ensure there was no movement to the target perch when no sound was played. If there were more than 20% false flights to the target perch, that trial was excluded from the results. Results were also excluded if the 2 loudest sounds did not receive strikes in 80% of the times they were played. I imagine this was to rule out the owl either being too eager to land at the “food perch” or if the owl was in a bad mood and didn’t want to fly to the target perch.

The results showed that neither age or physical damage to the hairs themselves much affected the regeneration process. The one owl, Weiss, was observed over a period of 21 years (at 2, 17, 23 years old) and only lost the smallest bit of hearing at the very high frequency range.

Both age ranges had the best hearing between 2 and 8 kHz. At 0.5, 1.0, and 6.3 kHZ the hearing ability of the older owls was slightly better than the younger group. At the other remaining frequencies, the younger group did better, but not by enough to be statistically significant.

The line for Konishi in the above graph are results obtained from a test in the 1970’s in Japan that was done to replicate the results of owls being able to hunt in total darkness using sound that I wrote about in the summary of Payne’s testing, which can be found here. Results were comparable, but that was only testing of a single owl, and it was a different species of Barn Owl than the ones in this experiment.

Here is the lifetime data for Weiss. Initial testing was done at 18-22 months old, when owl hearing finished developing. He was tasted again in these 2 rounds of experiments at ages 17 and 23. While there was some loss of very high frequency hearing over time, at the 12 kHZ range. The other frequencies showed slight deterioration, but only by a few decibels, so they interpreted that as a change in hearing more than actual deterioration.

The change was even less significant between ages 17-23, with some frequency responses seeming to have improved a tiny bit. As most wild Barn Owls do not live more than 3 or 4 years, this shows that over even an owl’s maximum expectant lifespan, there is no significant deterioration of hearing quality in a way that would negatively impact them.

Typical age-related hearing loss in mammals leads to a threshold (range of volumes and frequencies they can hear) increase of 20-40 decibels, while even over the course of a very long-lived owl’s life, the increase was only 4-10 decibels. While many owls die early, this shows it is not due to hearing degradation related issues. While the majority do not live longer than 3-4 years, it is not rare to find ones 10-20 years of age.

While younger owls were as a group more sensitive to sound that the old owls, it was by less than 3 decibels different in threshold. Overall statistical testing showed no significant difference in hearing ability between the two groups.

Other experiments over the years have shown pigeons, chickens, finches, budgies, European starlings, quails, and more have all been able to regrow hairs of the basilar papilla removed chemically in about 4-6 weeks with no significant loss in original hearing ability. Physical damage to the hairs by acoustic trauma (hitting them with high pressure sound waves to break them by vibration) yielded very similar regrowth and regaining of hearing to a remarkable degree.

The ability to regrow these hairs seems to be key to this amazing ability of birds as had been previously hypothesized due to testing on some of those other birds. Further study of this process will hopefully help us to find treatments to help us in the future to treat this widespread issue of humankind. While most of us will eventually suffer from some extent of hearing loss, it is something most birds will never have to deal with, no matter how long they live. Hopefully in the future, we will learn their secret and share in the joy of a long life full of vibrant sound.

African savannah elephants (Loxodonta africana) are the world's largest living land-based animals, reaching a height between 10 and 13 feet (roughly 3 to 4 meters) and weighing between 4 to 7 tons. One in particular, Doma, is the most dominant male in his group. Yet he seems to have developed this superiority as much through charisma and kindness as from sheer girth. All the other elephants in his herd run to him at the first sign of trouble; during calmer times, they willingly present him with their rumps in a seeming sign of submission...

Via @jeffw

cross-posted from: https://lemmy.world/post/15757735

I was reading more about owl vocalizations and had a hard time making much of the actual research paper as I don't know much about statistics or acoustics. I think I got the jist of it, but this is probably more informative for you than it is for me, so I thought I'd share the post with you.

I'm sure things like this are being used in projects like BirdNET-Pi and in ongoing research.

Post based on: The assessment of biases in the acoustic discrimination of individuals Pavel Linhart (2017)

Owl live lives that are largely based on sound. This lets them have an almost omniscient view of the world around them. Being able to hear their world from a distance lets them stay in one location, allowing them to stay safely hidden while not having to fly around expending crucial energy to monitor their territories.

Pavel Linhart of the University of South Bohemia has studied many animal vocalizations to try and understand all the things they are able to communicate. Sound samples of animals are recorded, analyzed, and characteristics are removed with an algorithm to determine the contents of the animal’s message. These messages can contain body size, emotional states, and the identity of individuals among other things. Little Owls made a great species for Linhart to study. They live close together, do not migrate, and stay in a relatively small range, making them easy to work with.

The sounds are looked at by duration, frequency, and “colorations,” which seem to be small changes to basic calls. These differences can be analyzed and used to help determine both the number of individuals in a population, but also who those individuals are, with the goal being to allow individual monitoring through sound, basically being able to see the sounds of owl (or other animals) the way the owls themselves do; to know who is where and doing what.

One of the key takeaways from his research is that variations between individuals grow along with the density of the owl population. The conclusion drawn is there are benefits from having uniquely distinct sound signatures for individuals. Owls can communicate their presence to others and be identified as known owls, saving them the energy of investigating potential intruders to their territory. Owl calls do not change much over time, so even if they only encounter each other once a year for mating season, they can identify each other over great distance, year after year. There is also benefit to researchers, as it brings them closer to being able to use those same sounds to monitor individual animals using recorded sound.

To demonstrate some of the variations between individuals, Linhart has also published a Little Owl Match Game. There are 16 “cards,” each containing a recording of a Little Owl (and some simulated owls) for you to try to successfully match the calls as if you where the algorithm trying to match the sound to a known individual. You can play the game here.

In a related story, researcher Karla Bloem was studying Great Horned Owl calls when she met Baroque music specialist Marjon Savelsberg, who fell in love with the sounds of owl calls and became a virtual assistant volunteering to try to pick out individual owls by their vocalizations.

Her musical training made her very successful to pick out these individual variations between individual calls. She is now using her abilities to work with Eurasian Eagle Owls in her native Netherlands.

Savelsberg with a baby Eagle Owl

cross-posted from: https://lemmy.sdf.org/post/16469373

It was recommended by a reader that I share this here. It does seem like the type of thing you'd enjoy from looking at some other posts, and perhaps some of you would enjoy seeing the charts in the full report and possibly be able to ELI5 about some of the more detailed findings that went over my head.

cross-posted from: https://lemmy.world/post/14465710

In reading Jennifer Ackerman’s Book, What an Owl Knows, many interesting scientific papers are mentioned, detailing some of the journey to our current level of owl understanding. Many of these are available online, but they are not always the most approachable things to read. I’ve bookmarked a few to explorer and try to share with you in a more friendly and condensed manor.

Today’s is a study about how we learned about owl’s amazing hearing abilities and how we began to understand their 3-dimensional ability to understand sound. It’s a hugely useful ability in how they get their food, and to stay one step ahead of their own predators. Knowing more about this will allow you to better understand these amazing animals and to get a deeper feel for how they are able to do some of the things they do.

ACOUSTIC LOCATION OF PREY BY BARN OWLS {TYTO ALBA) BY ROGER S. PAYNE Rockefeller University and New York Zoological Society Received 20 January 1970

Studies go back to the 1930s and 1940s to determine how owls locate their prey in the dark. After checking the minimum distance in low light for owls to both locate prey and navigate to it while avoiding obstacles on moonless nights under tree cover making light even less available it started to become evident the owls had some other means of navigating a lightless world.

One early theory proposed owls were able to see infrared. This was quickly rules out by seeing the owls eye did not have the proper anatomy to do so, and exposing owls to incredibly high levels of infrared light produced no response in the irises. This ability would also not explain how owls could see prey obscured by grass or snow tunnels.

After that, a theory was circulated that they used a heightened sense of smell. This never seemed to make it far into experimentation. Birds in general other than vultures are not known to have well developed sense of smell, and the distances owls would need to smell prey seemed extreme. Also in many of the experiments involving darkness, other observers had noted owls would many times bump into or step on the dead rodent specimens before noticing them.

Echolocation was also ruled out in the 1950s after another series of low light experiments determined at a certain darkness, owls lost the ability to avoid obstacles. If owls could echolocate, they would be able to avoid the obstacles in any light level.

Prior to Payne’s research, it was known many owls had asymmetrical ears that were thought to contribute to the owls’ ability to locate prey. What was not likely understood was just how much the structures contributed to those abilities. It was very difficult to examine the structure of the ear flaps, as most attempts to remove the flap feathers to see the actual flaps would destroy the flaps themselves. With Payne’s successful attempts, it was able to be seen the drastic increase in hearing ability the owl gained from being able to contort the angle of the flaps to create near parabolic structures to magnify available sound.

The ear flap feathers are unusually thick and are the densest packed feathers on the owl’s body, positioned about as close as physically possible, in a hexagonal structure. The skin surrounding these feathers is also exceptionally thick. All this adds up to a structure that can collect and reflect sound to an extraordinary degree. The heart shape of the facial disc splits incoming sound equally between sides of the face, directing it straight to the ears.

The feather structures of the face and ears themselves do not have a reducing effect on incoming sound either. A microphone placed in an owl’s ear only measured a <1 decibel reduction in sound across a wide spectrum.

Even the downward facing beak and tilting down posture of the head play a role in sound delivery. Most birds have horizontal beaks, while owls’ beaks point down to the chest. This removes it as an obstacle to incoming sound. By having a downward curving beak and holding the head so the beak is tucked in even more removes the largest blockage to the parabolic shape of the face.

There are numerous inner ear structures of the owl which are different to most other birds. They have larger cochlea and ear drums than average, and the ear drums extends into the cochlear fluid to better transfer vibrations and to amplify low energy sounds. Inner ear structures are symmetrical. The asymmetrical external structures seem to be the only parts shaped differently on opposing sides. There are also 3 large air chambers in the owl skull, making up to 25% of the volume of the head. These openings are connected to the middle ear structures, possibly allowing sounds from one side to be heard by both ears.

Payne participated in prey location experiments using owls in a darked room. The windows were sealed with Masonite and electrical tape over the windows. After ensuring no light appeared to be entering the room, the confirmed it by leaving camera film exposed on the floor and then overdeveloped it to confirm no light was entering the room. They also only conducted the experiments at night on top of everything else.

The room was equipped with 2 inches (5cm) of leaf cover on the floor, and a 7 foot (2.13 m) perch was placed for the owl to hunt from. A hand raised barn owl was given 5 weeks to adjust to living in the room in increasing amounts of darkness.

For the experiment, a live deer mouse was released in the room. During the first 3 nights, the owl did not attempt to catch the mouse. Starting the fourth night, the owl did go after the mouse. Over the next few days, there were 16 attempted strikes on the mouse at a distance of >12 feet (3.66 m) with only 4 misses, and no miss was by greater than 2 inches (5 cm).

The ability to use infrared or smell was ruled out by dragging a mouse sized ball of paper at the same temperature as the surrounding leaves across the room and it was successfully captured by the owl. Being the same temperature would leave no infrared difference from the surroundings, and the paper did not smell like a mouse or anything else the owl would eat. This seemed to leave passive acoustic location as the means the owls hunted. The next series of tests involved blocking one ear with cotton and releasing the mouse. With either ear closed off, the owl was able to determine the correct direction of the mouse, but the strikes came up 18 inches (46 cm) short. After the failed attempt, the cotton was removed and all subsequent strikes caught the mouse.

These experiments were successfully duplicated at a similar test room at Cornell. Further experiments there were done replacing the leaf layer with sand, sand with small piles of leaves, or a leaf tied to the mouse’s tail. Tests were also done in the light and different levels of darkness to see if the light level affected the owl’s striking position or the way it hunted. Hundreds of strikes were observed or recorded, and after the owl got accustomed to hunting in the light, there were no significant differences noted. Strikes in total darkness were viewed with infrared light.

Observations were able to be made of the owls changing direction or following the mouse with their face if the mouse moved while the owl was coming at it. The mouse holding still is the only thing that kept the owl from locating it in the darkness. As soon as it moved a significant amount, the owls were able to locate it no matter how dark the room was.

Some interesting notes were discovered in observing strikes in the light. The owls did not normally have their talons open until they were about 6 inches (15 cm) of the mouse, and also in 22 out of 24 strikes, the owls would give a final wing flap within striking distance to make a last minute acceleration at the mouse just as the feet came forward. No strike itself killed the mouse. The owls would apply a crushing grip to prevent the mouse escaping or biting them.

Owls did not seem to do much of their unusual head movements in total darkness. This leaves it open for further testing to see if the head bobbing and turning upside down is to aid in hearing or in vision. Other differences in hunting in darkness included the owls would fly at about half speed, and would also swing their legs like a pendulum during flight. It was thought this was to reduce any injury due to collisions with unseen objects.

The way an owl aligns with its target is also quite interesting. When the owl dives, it lowers its head to near where the feet are positioned. It then goes face first at the prey, until the last moment where it flips the feet to be where the ears were, negating the need to adjust the calculation of the distance from the ears to the target to that of the feet. The talons are opened near equilaterally and evenly spaced to create the largest grasping area possible and conforming roughly to the shape of the mouse’s body.

Another experiment was done to see if owls could determine the direction the prey was facing. A dead mouse with a leaf attached was dragged across the floor 12 times. In all 12 strikes, the owl oriented itself to have the talons come in parallel to the mouse, maximizing grasping area. The thought was a miss in potentially better than a strike landing only 1 talon, as then they could not get a secure grip on the mouse, which could lead to the owl being bitten by the unrestrained mouse. The owl would always adjust its flight path, even in total darkness, to come in with the talons lined up with the length of the mouse’s body.

Some further tests were done about frequency owls can hear and some calculations to determine how far away an owl will strike at a sound. Payne’s calculations based one the mouse’s size relative to the claw spread of the test owl determined a maximum distance of 20 feet (6 m), which correlated to observed strike distance of a maximum of 23 feet (7 m), making the calculated distance fairly accurate.

Many of the total darkness tests were attempted with other owls with different ear structures. Testing with 2 Screech Owls and 3 Great Horned Owls were unsuccessful on all attempts. Those species both have symmetrical ears. Experiments with Saw Whet Owls and Long Eared Owls were successful, even though both of those species use different physiological methods to achieve the asymmetry. Saw Whets have asymmetrical skulls, Long Eared Owls have asymmetrical membranes at the entrances to the ear canals, and Barn Owls have an operculum, a valve that changes the shape of the ear openings. Payne also mentions Barred Owls have yet another type of asymmetry, though it isn’t mentioned what that is. He states this implies evidence of the owls’ ability to locate prey acoustically has developed numerous times.

The results of all this testing show these owls have the ability to “see” sound in 3 dimensions, as they are able to determine frequency (tone/pitch), intensity (energy of the soundwave), phase (timing relationship between 2 soundwaves), and time-of-arrival (difference of time between both ears hearing a sound) of any observable sounds. They are able to internally calculate these values to track their prey. The time from observation to an attempted strike is lower the more head on the sound is coming to the owl, as it reduces the time of these calculations.

There were other experiments done that I don’t know how to interpret of Payne firing different sounds at a suspended dead owl with microphones placed in the ears and he created plots of how the sound is received and how the owl can interpret it, but that’s all beyond my level of understanding. Also some other ones where a dead mouse is moved while suspended on silk strands at different heights off the floor. The owls missed most of those strikes, and the thought seemed to be since the owls knew what the environment actually looked like in the light, they targeted past the actual mouse to the spot on the floor past the mouse if you would draw a line directly from the owl’s eyes through the actual location of the mouse, to the floor beyond.

Some earlier theories on how owls hear were ruled out, as those had stated the owl could visualize the sound regardless of the location of the source, but in all Payne’s experimentation, the owl always turned to face the sound directly before taking flight. The prior theory’s principles implied they could receive accurate location data no matter their facial orientation to the source. In his results, the owls required 2 sounds, and initial sound to alert them something was there and to get their head oriented to that sound, and then a follow up sound to focus in to determine the precise location.

There are more results concerning frequencies they are able to hear, and how they use them to determine sound location that are beyond my understanding and some explanations on how the head and ear flaps move to cycle through frequency ranges to maximize specific parts of sound they hear, so if you can understand any of that, the final summary of the paper will probably hold some more great insights for you. This is the best I can make of it though.

There’s a lot more to this paper than I presented here of course, it’s 36 pages of actual tests and results, and I’ve gotten this down to about 4. I know I’ve learned a good bit by reading it, and I hope you enjoyed this summary.

cross-posted from: https://lemmy.world/post/14352458

World faces ‘deathly silence’ of nature as wildlife disappears, warn experts

Loss of intensity and diversity of noises in ecosystems reflects an alarming decline in healthy biodiversity, say sound ecologists

Sounds of the natural world are rapidly falling silent and will become “acoustic fossils” without urgent action to halt environmental destruction, international experts have warned.

As technology develops, sound has become an increasingly important way of measuring the health and biodiversity of ecosystems: our forests, soils and oceans all produce their own acoustic signatures. Scientists who use ecoacoustics to measure habitats and species say that quiet is falling across thousands of habitats, as the planet witnesses extraordinary losses in the density and variety of species. Disappearing or losing volume along with them are many familiar sounds: the morning calls of birds, rustle of mammals through undergrowth and summer hum of insects.

Today, tuning into some ecosystems reveals a “deathly silence”, said Prof Steve Simpson from the University of Bristol. “It is that race against time – we’ve only just discovered that they make such sounds, and yet we hear the sound disappearing.”

“The changes are profound. And they are happening everywhere,” said US soundscape recordist Bernie Krause, who has taken more than 5,000 hours of recordings from seven continents over the past 55 years. He estimates that 70% of his archive is from habitats that no longer exist.

cross-posted from: https://feddit.uk/post/10578377

Soundscape ecology: a window into a disappearing world – podcast

What can sound tell us about nature loss? Guardian biodiversity reporter Phoebe Weston tells Madeleine Finlay about her visit to Monks Wood in Cambridgeshire, where ecologist Richard Broughton has witnessed the decline of the marsh tit population over 22 years, and has heard the impact on the wood’s soundscape. As species lose their habitats across the world, pioneering soundscape ecologist Bernie Krause has argued that if we listen closely, nature can tell us everything we need to know about our impact on the planet