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*  When Fish Eat Birds 
*  Why Do Little Birds Mob Big Birds? 
*  Shrikes: Meet the Bird That Impales Prey on Spikes 
*  Burrowing Owls Face an Uncertain Future 
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A wild turkey. © Kent
Mason
The ears of many species of  owls  are asymmetrical. For
example, in  barn owls  ( _Tyto alba_ ), the
placement of the two ear flaps (operculi) lying directly in front of the ear
canal opening is different for each ear. This asymmetry is such that the
center of the left ear flap is slightly above a horizontal line passing
through the eyes and directed downward, while the center of the right ear flap
is slightly below the line and directed upward. In two other species of owls
with asymmetrical ears, the  saw-whet owl  and the  long-eared owl  , the
asymmetry is achieved by different means: in saw whets, the skull is
asymmetrical; in the long-eared owl, the skin structures lying near the ear
form asymmetrical entrances to the ear canals, which is achieved by a
horizontal membrane. Thus, ear asymmetry seems to have evolved on at least
three different occasions among owls. Because owls depend on their sense of
hearing for hunting, this  convergent evolution  in owl ears suggests that asymmetry is important for
sound localization in the owl.
The Galapagos Islands’ wildlife is famous for its evolutionary adaptations.
The  vampire finch

is a notable example. This small bird usually feasts on a not-particularly-
noteworthy diet of insects and seeds. But during times of scarcity, the finch
switches to pecking at blue-footed and Nazca boobies, then sipping their
blood.
Stories of The Nature Conservancy
July 11, 2021
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5. **Claire Binkley** says:
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The well-developed facial ruff that owls have adapted has shown to help with
sound localization as the ruff works to funnel, trap, and focus sounds. The
ruff is located around the owl’s face and acts as a reflector for sound.  [19]
Owls have specific feathers on their head that help direct sound toward their
external ear openings, known as reflector feathers, as well as feathers that
help prevent the ruff from getting dirty, known as auricular feathers.
Reflector feathers sit around the border of the ruff, are very dense, and have
been found to help with the ramification of sounds.  [20]  Auricular feathers,
on the other hand, are located around the  facial disc  of the owl and, unlike reflector feathers, are very loose and
do not aid with the ramification of sounds.  [21]  Owls also have a third type
of feather, known as contour feathers, that are found everywhere on the owl’s
body except in the facial ruff, but do not at all assist in the ability to
localize sounds. Contour feathers are instead useful for things such as flight
and conservation of body heat.
##  Parallel processing pathways in the brain
Ability of owls to locate sounds in 3D space
The time and sound-pressure pathways converge at the lateral shell of the
central nucleus of the inferior colliculus. The lateral shell projects to the
external nucleus, where each space-specific neuron responds to acoustic
stimuli only if the sound originates from a restricted area in space, i.e. the
 receptive field  of that neuron.
These neurons respond exclusively to binaural signals containing the same ITD
and IID that would be created by a sound source located in the neuron's
receptive field. Thus their receptive fields arise from the neurons’ tuning to
particular combinations of ITD and IID, simultaneously in a narrow range.
These space-specific neurons can thus form a map of auditory space in which
the positions of receptive fields in space are isomorphically projected onto
the anatomical sites of the neurons.  [16]
The  cochlear duct  of the owl contains
the basilar papilla, the  tectorial membrane  , the tegmentum vasculum, and the macula of the lagena.
The basilar papilla of the cochlea was measured to be 9.5-11.5 mm long.
Proximal sensory hair cells contained mostly short hair cells along with a few
intermediate hair cells, but absolutely no tall hair cells. Tall hair cells
are only present on the distal half of the owl’s papilla, starting at about 5
mm from the proximal end, along with some short-haired cells. The distal tip
of the papilla is occupied exclusively by tall hair cells, whereas the
proximal tip is occupied exclusively by lenticular cells.  [6]
##  Introduction to sound localization
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From Wikipedia, the free encyclopedia

Biological sound detection process

This article is about the biological process of sound localization. For sound
localization via mechanical or electrical means, see  acoustic location
 and  3D sound localization
 .

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](/wiki/Wikipedia:Manual_of_Style/Lead_section
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Auditory transmission stereo system  

This kind of sound localization technique provides us the real virtual 
stereo system  .  [25]  It utilizes
"smart" manikins, such as KEMAR, to glean signals or use DSP methods to
simulate the transmission process from sources to ears. After amplifying,
recording and transmitting, the two channels of received signals will be
reproduced through earphones or speakers. This localization approach uses
electroacoustic methods to obtain the spatial information of the original
sound field by transferring the listener's auditory apparatus to the original
sound field. The most considerable advantages of it would be that its acoustic
images are lively and natural. Also, it only needs two independent transmitted
signals to reproduce the acoustic image of a 3D system.

 Sound
localization with manikin
Effect of a hearing loss  

A number of studies have looked into the effect of hearing loss on interaural
time differences. In their review of localisation and lateralisation studies,
Durlach, Thompson, and Colburn (1981), cited in Moore (1996) found a "clear
trend for poor localization and lateralization in people with unilateral or
asymmetrical cochlear damage." This is due to the difference in performance
between the two ears. In support of this, they did not find significant
localisation problems in individuals with symmetrical cochlear losses. In
addition to this, studies have been conducted into the effect of hearing loss
on the threshold for interaural time differences. The normal human threshold
for detection of an ITD is up to a time difference of 10μs (microseconds).
Studies by Gabriel, Koehnke, & Colburn (1992), Häusler, Colburn, & Marr (1983)
and Kinkel, Kollmeier, & Holube (1991)(cited by Moore, 1996) have shown that
there can be great differences between individuals regarding binaural
performance. It was found that unilateral or asymmetric hearing losses can
increase the threshold of ITD detection in patients. This was also found to
apply to individuals with symmetrical hearing losses when detecting ITDs in
narrowband signals. However, ITD thresholds seem to be normal for those with
symmetrical losses when listening to broadband sounds.
A great blue heron snatches a gosling. © Mark Koster/TNC Photo Contest 2019
##  Primary Navigation
July 7, 2021
Bi-coordinate sound localization (owls)  ") ]

Main article:  Sound localization in owls 

Most owls are  nocturnal  or  crepuscular
  birds of prey  . Because they hunt at night, they must rely on non-visual
senses. Experiments by Roger Payne  [31]  have shown that owls are sensitive
to the sounds made by their prey, not the heat or the smell. In fact, the
sound cues are both necessary and sufficient for localization of mice from a
distant location where they are perched. For this to work, the owls must be
able to accurately localize both the azimuth and the elevation of the sound
source.
How sound reaches the brain  

Sound is the perceptual result of mechanical vibrations traveling through a
medium such as air or water. Through the mechanisms of compression and
rarefaction, sound waves travel through the air, bounce off the  pinna
 "Pinna \(anatomy\)") and concha of the exterior ear,
and enter the ear canal. In mammals, the sound waves vibrate the tympanic
membrane (  ear drum  ), causing the three bones
of the  middle ear  to vibrate, which then
sends the energy through the  oval window 
and into the  cochlea  where it is changed into a
chemical signal by  hair cells  in the 
organ of Corti  , which  synapse
 onto  spiral ganglion  fibers that travel through the  cochlear nerve
 into the brain.
Wikilink_to_citation_does_not_work "Template:Harvard citation documentation") _ ]  I  T  D  =  {  3  ×  r  c  ×  sin  ⁡  θ  ,  if  f  ≤  4000Hz  2  ×  r  c  ×  sin  ⁡  θ  ,  if  f  > 4000Hz  {\displaystyle ITD={\begin{cases}3\times {\frac {r}{c}}\times \sin \theta ,&{\text{if }}f\leq {\text{4000Hz }}\\\2\times {\frac {r}{c}}\times \sin \theta ,&{\text{if }}f>{\text{ 4000Hz}}\end{cases}}}   . In above closed form, we assumed that the 0 degree is in the right ahead of the head and counter-clockwise is positive.
* Interaural intensity difference (IID) or interaural level difference (ILD) – Sound from the right side has a higher level at the right ear than at the left ear, because the  head shadows  the left ear. These level differences are highly frequency dependent and they increase with increasing frequency. Massive theoretical researches demonstrate that IID relates to the signal frequency  f  {\displaystyle f}   and the angular position of the acoustic source  θ  {\displaystyle \theta }   . The function of IID is given by:  [8]  [ _[ citation not found  ](/wiki/Template:Harvard_citation_documentation
##  Continue Exploring
* ###  Crows
Signal processing  

Sound processing of the human auditory system is performed in so-called 
critical bands  . The  hearing range
 is segmented into 24 critical bands,
each with a width of 1  Bark  or 100  Mel
 . For a directional analysis the signals inside
the critical band are analyzed together.

The auditory system can extract the sound of a desired sound source out of
interfering noise. This allows the listener to concentrate on only one speaker
if other speakers are also talking (the  cocktail party effect
 ). With the help of the
cocktail party effect sound from interfering directions is perceived
attenuated compared to the sound from the desired direction. The auditory
system can increase the  signal-to-noise ratio  by up to 15  dB  , which
means that interfering sound is perceived to be attenuated to half (or less)
of its actual  loudness  .  [ _ citation needed
 _ ]

In enclosed rooms not only the direct sound from a sound source is arriving at
the listener's ears, but also sound which has been  reflected
 "Reflection \(physics\)") at the walls. The
auditory system analyses only the direct sound,  [12]  which is arriving
first, for sound localization, but not the reflected sound, which is arriving
later (  law of the first wave front  ). So sound localization remains possible even in an echoic
environment. This echo cancellation occurs in the Dorsal Nucleus of the 
Lateral Lemniscus  (DNLL).  [24]

In order to determine the time periods, where the direct sound prevails and
which can be used for directional evaluation, the auditory system analyzes
loudness changes in different critical bands and also the stability of the
perceived direction. If there is a strong attack of the loudness in several
critical bands and if the perceived direction is stable, this attack is in all
probability caused by the direct sound of a sound source, which is entering
newly or which is changing its signal characteristics. This short time period
is used by the auditory system for directional and loudness analysis of this
sound. When reflections arrive a little bit later, they do not enhance the
loudness inside the critical bands in such a strong way, but the directional
cues become unstable, because there is a mix of sound of several reflection
directions. As a result, no new directional analysis is triggered by the
auditory system.

This first detected direction from the direct sound is taken as the found
sound source direction, until other strong loudness attacks, combined with
stable directional information, indicate that a new directional analysis is
possible. (see  Franssen effect  )
Another demonstration of the importance of ear asymmetry in owls is that, in
experiments, owls with symmetrical ears, such as the  screech owl
 ( _Otus asio_ ) and the  great horned owl
 ( _Bubo virginianus_ ), could not
be trained to locate prey in total darkness, whereas owls with asymmetrical
ears could be trained.  [18]
Owls are very adept nocturnal predators, hunting prey that includes small
mammals, reptiles, and insects. They are able to rotate their head up to 270
degrees, lock onto prey, and launch a silent attack. Owls lock onto prey by
using sound localization.  [2]  Sound localization is an animal’s ability to
identify the origin of a sound in distance and direction.  [3]  Several owl
species have ears that are asymmetrical in size and location, which enhances
this ability. These species include barn owls ( _Tyto alba_ ), northern saw-
whet owls ( _Aegolius acadicus_ ), and long-eared owls ( _Asio otus_ ). The
barn owl ( _Tyto alba_ ) is the most commonly studied for sound localization
because they use similar methods to humans for interpreting interaural time
differences in the horizontal plane.  [4]  This species has evolved a
specialized set of pathways in the brain that allow them to hear a sound and
map out the possible location of the object that elicited that sound. Sound
waves enter the ear via the ear canal and travel until they reach the tympanic
membrane. The  tympanic membrane  then sends these waves through the  ossicles  of the middle ear and into the inner ear that includes the 
vestibular organ  ,  cochlea
 , and  auditory nerve  . They are then able to use interaural time difference (ITD)
and interaural level difference (ILD) to pinpoint the location and elevation
of their prey.
Herons eat terrestrial prey, too. I often see them lined up in area fields,
hunting the aforementioned voles and other small mammals. I also see them
stalking around bird nesting areas, and songbirds mob them  just as they
would a raptor  . They even eat snakes and  baby alligators
 , stuffing
seemingly impossible prey down their throats.
In the case of the American crow, though, much of what we think we know about
their diet is likely wrong. The site  Corvid Research notes

that many people believe roadkill is a key component of crow diets, for
instance. However, research found that roadkill makes up less than five
percent of their calories.
Specific techniques with applications
Human auditory system  

Sound localization is the process of determining the location of a  sound
 source. The brain utilizes subtle differences in
intensity, spectral, and timing cues to allow us to localize sound sources.
[3]  [4]  In this section, to more deeply understand the human auditory
mechanism, we will briefly discuss human ear localization theory.

Localization can be described in terms of three-dimensional position: the
azimuth or horizontal angle, the elevation or vertical angle, and the distance
(for static sounds) or velocity (for moving sounds).  [5]

The azimuth of a sound is signaled by the  difference in arrival times
between the ears  , by the relative amplitude of high-frequency sounds (the shadow
effect), and by the asymmetrical spectral reflections from various parts of
our bodies, including torso, shoulders, and  pinnae 
"Pinna \(anatomy\)") .  [5]

The distance cues are the loss of amplitude, the loss of high frequencies, and
the ratio of the direct signal to the reverberated signal.  [5]

Depending on where the source is located, our head acts as a barrier to change
the  timbre  , intensity, and  spectral
 qualities of the sound,
helping the brain orient where the sound emanated from.  [4]  These minute
differences between the two ears are known as interaural cues.  [4]

Lower frequencies, with longer wavelengths, diffract the sound around the head
forcing the brain to focus only on the phasing cues from the source.  [4]

Helmut Haas discovered that we can discern the sound source despite additional
reflections at 10 decibels louder than the original wave front, using the
earliest arriving wave front.  [4]  This principle is known as the  Haas
effect  , a specific version of the 
precedence effect  .  [4]  Haas
measured down to even a 1 millisecond difference in timing between the
original sound and reflected sound increased the spaciousness, allowing the
brain to discern the true location of the original sound. The nervous system
combines all early reflections into a single perceptual whole allowing the
brain to process multiple different sounds at once.  [6]  The nervous system
will combine reflections that are within about 35 milliseconds of each other
and that have a similar intensity.  [6]
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From Wikipedia, the free encyclopedia

Difference in time that it takes a sound to travel between two ears

_entre_izquierdo_\(inferior\)_y_correcto_\(superior\)_orejas.jpg)
**Interaural time difference** (ITD) between left (top) and right (bottom)
ears. (sound source: 100 ms  white noise 
from 90°  azimuth  , 0°  elevation
 )

The **interaural time difference** (or **ITD** ) when concerning humans or
animals, is the difference in arrival time of a sound between two ears. It is
important in the  localization of sounds  , as it provides a cue to the direction or angle of the sound
source from the head. If a signal arrives at the head from one side, the
signal has further to travel to reach the far ear than the near ear. This
pathlength difference results in a time difference between the sound's
arrivals at the ears, which is detected and aids the process of identifying
the direction of sound source.

When a signal is produced in the horizontal plane, its angle in relation to
the head is referred to as its  azimuth  , with 0
degrees (0°) azimuth being directly in front of the listener, 90° to the
right, and 180° being directly behind.
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The inner ear of barn owls includes the vestibular organ, cochlea, and
auditory nerve. The anatomy of the inner ear in barn owls was studied in an
experiment where three owls were utilized and fixed at laboratories by the
intravascular perfusion of 1%  formaldehyde  and 1.25%  glutaraldehyde  in a 0.1 phosphate buffer.  [5]  The temporal lobes of the
owls were then removed from the skulls, post-fixed in 1%  osmium tetroxide
 , dehydrated, then embedded in 
Araldite  to study the anatomy of the inner ear.
This study revealed that the  basilar papilla  of barn owls has two unique features being a proliferation
of lenticular cells and a thickening of the basilar membrane.
Most owls are  nocturnal  or  crepuscular
  birds of prey  . Because they hunt at night, they must rely on non-visual
senses. Experiments by Roger Payne  [1]  have shown that owls are sensitive to
the sounds made by their prey, not the heat or the smell. In fact, the sound
cues are both necessary and sufficient for localization of mice from a distant
location where they are perched. For this to work, the owls must be able to
accurately localize both the azimuth and the elevation of the sound source.
Neural interactions  

In  vertebrates  , interaural time
differences are known to be calculated in the  superior olivary nucleus
 of the 
brainstem  . According to  Jeffress
 ,  [1]  this calculation relies
on  delay lines  :  neurons
 in the superior olive which accept innervation from
each ear with different connecting  axon  lengths. Some
cells are more directly connected to one ear than the other, thus they are
specific for a particular interaural time difference. This theory is
equivalent to the mathematical procedure of  cross-correlation  . However, because Jeffress's theory is
unable to account for the  precedence effect  , in which only the first of multiple identical sounds is
used to determine the sounds' location (thus avoiding confusion caused by
echoes), it cannot be entirely used to explain the response. Furthermore, a
number of recent physiological observations made in the midbrain and brainstem
of small mammals have shed considerable doubt on the validity of Jeffress's
original ideas.  [2]

Neurons sensitive to interaural level differences (ILDs) are excited by
stimulation of one ear and inhibited by stimulation of the other ear, such
that the response magnitude of the cell depends on the relative strengths of
the two inputs, which in turn, depends on the sound intensities at the ears.

In the auditory midbrain nucleus, the  inferior colliculus
 (IC), many ILD sensitive
neurons have response functions that decline steeply from maximum to zero
spikes as a function of ILD. However, there are also many neurons with much
more shallow response functions that do not decline to zero spikes.
Provide_an_accessible_overview
"Wikipedia:Manual of Style/Lead section") of all important aspects of the
article.  _( April 2023  ) _

---|---

**Sound localization** is a listener's ability to identify the location or
origin of a detected  sound  in direction and distance.

The sound localization mechanisms of the mammalian  auditory system
 have been extensively studied. The
auditory system uses several cues for sound source localization, including
time difference and level difference (or intensity difference) between the
ears, and spectral information. Other animals, such as birds and reptiles,
also use them but they may use them differently, and some also have
localization cues which are absent in the human auditory system, such as the
effects of ear movements. Animals with the ability to localize sound have a
clear evolutionary advantage.
##  Author:  Matthew L. Miller