PHYS341/2024/Project36

The Skeleton of Primoptynx Poliotaurus

Historical Overview

Owls, part of the Strigiformes family, are often overlooked due their deceitful and nocturnal presence. Having over 250+ unique species, these birds have a long evolutionary history. The First documented owl fossil Primoptynx poliotauros, dates all the way back to around 61 million years ago. Making them the longest living family birds of prey following the extinction of the dinosaurs. Unlike most other birds of prey, the owl's evolution has mainly served to benefit its ability to hunt at night. Which led to a flatter facing skull and morphed eye sockets which are magnified to increase visual focus. Owls most notable characteristic is the ability to ability to turn their neck 360 degrees which assists in locating sounds and compensates for the lack of direction the modified retina provides.  

Although owls most commonly hunt in the night, they are not limited to excursions in the dark. Overwhelmingly, 69 percent of owls have evolved to be nocturnal while the remaining 31 percent hunt during the day or at dusk. This variability in behavior has also impacted the way each species of owl hoots while it’s awake.  

Vocal Tendencies:

Owls choose to hoot for a variety of different reasons; whether it's to find love, mark new territory, or even warn incoming intruders, these birds can achieve a unique harmonic tone which no other species can. Similar to humans, an owl's genetics plays a large factor in how they sound. For instance, an owl's gender or even size and either increase or decrease the pitch of pure tones produced . Additionally, wider or more narrow trachea (located inside an owl's neck) can also severely impact the oscillation of air which takes place.

Anatomy of the Syrinx

The syrinx of a non-passerines (owl family)

The Syrinx, is an auditory organ which is responsible for the production of sound in almost all birds. This narrow airway is built at the base of the trachea (caudal end ) just before it splits, leading to the lungs. Tiny “vocal folds” surrounded the fork of the trachea allow air to flow in and out. The cycle of inhalation and exhalation supplies these vocal folds with adequate air flow and pressure which then oscillates the “membrana tympaniformis” (membrane wall) intermittently placed between the vocal folds.

Syrinx Membrane:

Being a subsection of the trachea, The Syrinx must also be densely structured in that it can support the respiratory flow of air into the lungs. In doing so, the treachery is lined with a thin lining of membrane which helps air pass by reacting and oscillating depending on how the syrinx vocal folds open and close. The continuous oscillation of this membrane is what actually creates interpretable sound. In other words, the Syrinx acts as a navigator of sorts. Fluctuating air flow and pressure through the trachea acting as the catalyst. What makes birds' vocal tract particularly special is that their vocal folds sit on the side of the trachea unlike the middle in humans. The unique placement of these vocal folds allows owls to emulate noises with multiple pure tones in a singular breath. Meaning that they can create sounds which us humans cannot.

What makes birds' vocal tract particularly special is that their vocal folds sit on the side of the trachea unlike the middle in humans. The unique placement of these vocal folds allows owls to emulate noises with multiple pure tones in a singular breath. Meaning that they can create sounds which us humans cannot.

Measuring Owl Acoustics

Snowy Owl

Snowy Owl Spectrum Graph

Elf Owl

Elf Owl Spectrum Graph

Flammulated Owl

Flammulated Owl Spectrum Graph

Burrowing Owl

Burrowing Owl Spectrum Graph

Converting data:

What's unanimous about vocals owls create is the steady hum they emit. Most owls produce a very clear pure tone which can be heard from miles away. Studies show that as owls have evolved so has the shape and length of the Syrinx. Modern day owls and familiar birds of prey, have adopted a more narrow and longer syrinx to allow for higher vocal pressure and surpassed efficiency in high frequencies . These differences in syrinx differ from one owl species to another, but we can compare and draw conclusions from listening to different owl produce their own hoots. If we wanted to accurately access the exact power to db level present inside of a given owls syrinx, we can use the following equation to convert the amount of air pressure produced inside the trachea into measurable db.

$p_{r}$ = Radiated Power

$R$ = Being the radius of the trachea

$SPL$ = The amount of air pressure level

Spectrum Interpretation:

Alternatively, for this demonstration to make things easier, by converting the recorded vocal sounds into a spectrum graphs. Measuring the results we can see that Elf owl consists of having the highest hz frequency output when compared to its sister species .This is consistent with current theories which hypothesize that, owls with thinner and longer syrinx produce larger displacements of pressure resulting in louder more pure sounds.

Elf Owl:

The smallest owl in the world, the Elf Owl lives in the woodlands and Saguaro cactus-studded deserts of the southwestern U.S. and Mexico. This species' “chatter song” consists of a fast series of five to seven high-pitched notes that some have compared to the yipping of a small dog.

• Peak Frequency of 1629 hz

Snowy Owl:

Snowy Owl during Migration to the Mid-coast due to cyclical peaks in breeding success in their Arctic home.

The Snowy Owl can be heard from up to seven miles away on the open Arctic tundra. Famous for their white plumage, Snowy Owls have what's called a circumpolar range, spanning northern regions of Eurasia as well as North America.

• Peak Frequency of 484 hz

Burrowing Owl:

The Burrowing owls are a very unique species of owls. Unlike any other species they live underground. Their main call is a rather high-pitched (compared to other owls). made by the male as he woos a mate and defends a territory. Burrowing Owls are found in grassland and arid habitats throughout North and South America.

• Peak Frequency of 410 hz

Flammulated Owl:

This tiny, reddish owl, which could fit in the palm of your hand, spends its time foraging for insects near the tops of massive pine or fir trees. These aspects make it hard to spot, although its repetitive, low-pitched hoot is easier to notice. Flammulated owls live mainly in forests of large trees and are highly migratory.

• Peak Frequency of 967 hz

Conclusion

Owls have a distinct and remarkable ability to manipulate pure tones. Due to the complexity of the syrinx, an extension of the trachea found solely in particular species of birds and driven by a millennia of evolutionary changes. This highly specialized trait influences the physics and production behind a simple hoot. Allowing for more efficient sound transformation and clarity, owls which are smaller in stature , can more effectively utilize these pure tones which has resulted in increased survival rates, and even increased migration success rates.