Bird Hearing - How Are Birds Special

                                     Great Gray Owl Showing Pronounced Facial Disc  [Internet Photo]

Birds have incredible sight and hearing abilities.  Being around them, it does not take long to realize they are much more visually and auditorily acute than we humans.  This post will discuss hearing in birds and try to explain some of the reasons birds are so 'blessed'.

Birds depend on sight and hearing to locate food, to navigate, to protect themselves and their offspring from harm and predators, and to locate mates and other members of their species.  The Trichomonas victims (House Finches) we are seeing this winter around some feeders are a good example of how handicapped a bird is without good sight or hearing.  

                               Barn Owl Showing Edge of Facial Disc  [Internet Photo]

Hearing is the second most important sense possessed by a bird, second to sight.  Birds can hear sounds located at a much greater distance and much lower in frequency than we can hear.  We have had a flock of Wild Turkeys visiting our yard lately and the slightest sound in the house causes them to raise their heads and look at the house.  The same is true of the many migrants arriving daily to feed.

Let's begin by describing how bird anatomy assists their hearing.  Not all birds are the same but many species have developed anatomical features that enhance their hearing abilities.  These features involve the head mainly.  Owls, for example, need acute hearing since they hunt mainly at night.  They often feed on rodents and they need to be able to hear a vole, for example, as it tunnels through heavy grass.  Owls have developed flat faces and facial discs which collect sound like a parabola.  Note the facial discs in the Great Gray Owl and the Barn Owl shown above.  The sound is collected by these discs and is funnelled to the ear openings.  Also note that the beaks of owls are positioned flat against the face (pointing downward) so that they do not distort the sound.  Head shape is also significant.  Studies have shown that the oval head shape of most birds helps with the processing of sound waves similar to the external ears of humans.  The feather ruffs on the face and around the facial discs work similarly.  Also do you know that they can change the shape of the facial disc as they wish in order to focus sound better?  

                                                    Great Horned Owl Showing Ear Tufts

Great Horned Owls and some other species (Long-eared Owl, Short-eared Owl, Eastern Screech-Owl) show ear tufts on their heads.  Let's make it clear.  These have nothing to do with hearing but are for display.  They are made of tufts of feathers and have no connection to the auditory system.  They do, however, sometimes help birders with finding and identifying the species.  I recently found a female Great Horned Owl hunkered down deeply in her nest and those ear tufts helped in finding her.

Birds do not have external ears (pinnae) like humans do.  They are descended from reptiles and external ears are not a reptilian trait.  They have, however, adapted wonderfully!  Their external ear canal openings (apertures) are on the sides of their heads.  If they have facial discs they are placed on the edges of the discs so that the sound is funnelled to them.  Some apertures are just covered with feathers for protection and to stop the muffled sound of air rushing past.  Some species have a cover over the aperture.  In some owls this covering (operculum) is round and acts like a valve.  In other species it is just a fold of skin.  

Many (most?) bird species have their apertures (ear openings) symmetrically placed on the sides of their heads.  Each side of the head matches the other.  Some species of owls, however, have asymmetrically set apertures.  The opening is set higher on one side of the head than on the other.  This is an amazing anatomical adaptation to enhance owl hearing.  Some other species of owls (Ural, Great Gray, Boreal, Saw-whet Owls) have another amazing adaptation.  They have asymmetry but it is in the temporal area.  There is an enlarged area on one side of the head in the area of the eye and where the jaw moves under the eye.  This slightly lop-sided anatomy is used to help improve sound acuity for these species.  

                    Northern Cardinal Showing Aperture (Auditory Opening) With Feathers Pulled Back

So how do birds locate the sound source accurately?  When a bird hears a sound it is able to pinpoint the direction it is coming from because the sound hits each ear at a different time.  This is a minute difference but an owl can detect a difference of 30 millionths of a second!  As the owl hears the sound it can tell which ear heard it first and it turns its head toward that direction. When the sound hits both ears simultaneously, it knows it is directly facing the source of the sound.   In owls with auditory openings unevenly placed on the head, they can tell better if the sound is coming from higher or lower areas.  So these owls can locate a sound in 4 ways; left, right, up or down.  These stimuli are computed instantaneously in the brain and the owl then knows exactly where the prey is located spatially.  

Owls have another adaptation to make them even more adept at prey location.  The area of the brain where sound is processed is called the medulla.  Studies have shown that owls have more complex medullae than other bird species.  A Barn Owl medulla is estimated to have 95,000 neurons which is 3 times more than crows! (Campbell, Wayne. 1994. Know Your Owls. Axia Wildlife).  Once the owl has located the prey it flies directly to it, keeping its head zeroed in on it.  If the prey moves, the owl does another quick calculation and adjusts its flight path.  

                                                Turkey Vulture Showing Auditory Opening

                           Black Vulture Showing Fold of Skin Over Aperture [Internet Photo]

                                     

                                       Wood Stork at Nest Showing Aperture  [Internet Photo]

Note the apertures (auditory openings) shown in the above photos.  I have selected featherless heads to make them more visible except for the cardinal.  Some birds have round apertures and some have slits.  Some have developed muscles which pull folds of skin over the aperture for protection.

The story of bird hearing is not complete without a word about what happens once the sound waves enter the ear canal.  Birds have a smaller hearing range to humans but they have a more acute sound recognition.  They are very perceptive to pitch, tone, and rhythm.  This translates into different sounds, calls and songs which they use for territory defence, sourcing food, protection against predators, etc. Some birds are capable of using echolocation (like bats).  These are cave-dwelling species and they use rapid chirps and clicks to navigate in dark caves.  Swifts are one species that uses echolocation.  

As in humans, as the sound enters the auditory canal it meets the tympanic membrane.  Here the similarity ends.  The tympanic membrane in birds is double.  The outer membrane protects the inner, more sensitive membrane.  The sound causes the tympanic membrane to vibrate and this vibration is transferred to the ossicular chain which transmits the vibration to the cochlea.  The ossicular chain is in 3 parts in humans but in only one part in birds.  This is called the columella.  The cochlea in birds is not spiral-shaped as in humans but is straight or banana-shaped.  The cochlea contains vibration-sensitive hair-like structures which transmit the sound stimuli to the medulla in the brain where it is interpreted for the bird.  

Birds hear over a wide frequency range.  They usually have a high degree of sensitivity in the low and middle range and it decreases rapidly as the frequency gets higher.  One study shows Bullfinches hear in the 100 to 12,800 Hertz range.  Pigeons can hear up to the 10,000 to 11,500 Hertz range.  The hearing range of most birds is from 1000 to 4000 Hz but it differs some among species (e.g. Long-eared Owl, 100 to 18,000 Hz).  Birds have another amazing hearing trait.  As we know, human hearing gets worse with age and with exposure to loud noises because of damage to the sensitive hair cells in the cochlea.  Not so with birds!   Avian hearing maintains itself over the life of the bird.  They do that by regenerating the sensitive hair cells in the cochlea as they wear out.  

And that is not all!  Bird hearing has even another amazing trait.  Birds living in temperate zones have hearing ability that fluctuates throughout the year.  When do they need better hearing?  During breeding season, of course.  They need to locate their mates, find their offspring, protect them, etc.  They need good hearing to do this.  Studies have shown that the auditory regions of their brains enlarge during breeding season.  Later in the season when song is not so important, that part of their brains then shrink.  

All this information puts 'birding by ear' in a new light.  We use bird sound to identify birds often in our study of birds.  It is good to think about how much more important hearing is to them.  It also makes us wonder about what noise pollution is doing to them.  How much damage is it causing to them physically and how does it disrupt their breeding and navigation behaviours?  And, what about airports where they are using noise to remove birds?  What is that doing to their hearing?  And, considering birds' ability to regenerate hair cells in the cochlea, would further study provide information which could help with neurodegenerative diseases in humans?  Without a doubt, birds are fascinating!!

Starlings Go To Roost

                                                        European Starling in Winter

The European Starling (Sturnus vulgaris) has become a very common resident of New Brunswick even though it is an introduced species.   Its former range was Europe.  It breeds throughout all of Europe.  It is a permanent resident in most of central and southern Europe.  It also winters in Spain and North Africa.  

How did it get here and become so common?  Well, it was brought to New York City in the 1890s by a group who were trying to bring to North America all the birds mentioned by Shakespeare.  They brought 100 European Starlings to Central Park and they were able to get a foothold from there.  The species found favourable habitat over most of North America and we now have a huge population.  It is estimated over 200 million European Starlings live from Alaska to Mexico.  

According to Squires in The Birds of New Brunswick, our first record was recorded by Moses in 1924.  Specimens were later taken or found in 1926 and 1928.  A nest was found in Salisbury in 1928.  The first record from Fredericton (Squires) was in 1929.  The population grew dramatically and they began to compete with our native Eastern Bluebirds for nesting sites which led to the decline in that species.  Starlings gather in huge flocks after the breeding season.  And that leads us to the topic of this post.

                                View From Shore Showing Piers From Former Fredericton City Bridge

                                            Close-up of Bridge Piers, Fredericton

Shown above are the piers for the former bridge crossing the St. John River at Fredericton.  One pier has a structure built on top which covers the top of the pier.  This was placed there in earlier times for an unknown purpose.  The interesting thing about this covering is that the Starlings have discovered that the area under it provides an excellent roosting site.  It is accessed from the side shown in the photo and provides a large covered area where the birds can roost in close proximity providing warmth and protection from predators.  I am surprised the birds are smart enough to discover this.  Maybe I shouldn't be!

                                                        European Starlings Entering Roost

It has been observed by local birders that large numbers of Starlings enter this roosting site at dusk.  Twice this last week I have watched this interesting spectacle.  Starlings appear in the sky in both small and large flocks.  The small flocks join the large flocks and they perform impressive aerial manoeuvres while getting organized in small groups to enter the roost.  In some ways it is similar to Chimney Swifts swirling over a chimney prior to going to roost.  What is different about the Starlings is that they 'murmur'.  We were able to watch this as they flew upward and around seemingly waiting for their chance to enter the roost. 

When Starlings murmur, the flock acts as one entity.  It swells and shrinks in one flowing unit.  It becomes a large ball which narrows in at the 'waist' and then falls out into a long rolling line.  It pulses, swirls and twists in a dance that looks choreographed.  While I watched I saw flocks of 50 to 100, flocks of 200 and one of 400 individuals.  I estimated there were about 1000 starlings going to roost that night.  It was reported by another birder that 1400 went to roost while he was watching.  All these birds entered the roost by flying into the face of the pier and slipping under the overhang of the top. This was done in groups of up to about 30 birds.  

I wondered where all the Starlings had come from.  Our Fredericton Christmas Count recorded 578 this year.  It appears that Starlings come in from outside the city to take advantage of this roost.  

This week the Starlings have another obstacle to getting into their roost, a Peregrine Falcon.  All the time we watched the Starling spectacle a Peregrine Falcon perched on one of the piers watching the Starlings.  It tried unsuccessfully a few times to catch one but the Starlings appeared to be faster and more agile than the falcon.  The falcon appeared to be a juvenile because it showed a bit of brown in its plumage.  That would explain its inexperience.  It is unusual to see a Peregrine Falcon in Fredericton so I was delighted to watch it.  Shown below is the Peregrine Falcon.

                                                    Peregrine Falcon Perched on Pier

I think it won't take long for the falcon to learn how to catch Starlings.  The flock seemed to perform without a lot of fear.  It is interesting that this spectacle was going on within a few hundred feet of the very core of downtown Fredericton.  The walkers and cyclists in the area were not even aware of it.  It is wonderful that some of our species have learned so well to adapt to our urban environments.

Wild Turkey - Life History

                                                                        Wild Turkey

The Wild Turkey (Meleagris gallopavo) is one of our largest birds.  It is a gallinaceous bird of the family, Phasianidae, order Galliformes.  It is the largest game bird in North America.  Originally the Wild Turkey was found in good numbers throughout most of continental US and in parts of  Mexico.  It occasionally spread into the extreme southern parts of Canada especially Manitoba, Ontario and New Brunswick.  Heavy hunting and habitat loss in the 1800s and 1900s extirpated it from most of its range.  Due to reintroduction programs and cessation of hunting it has now increased its population numbers over most of its original range.  Reintroduction programs in upper New York State and Maine have led to its range expansion into Ontario and New Brunswick.  

                                                            Wild Turkeys Feeding on Mixed Seed

Wild Turkeys provided a stable source of food for native Americans for countless years before the colonists arrived.  At that time the colonists could easily bag a turkey close to their homes.  They provided a good food source and so arose their popularity as a favourite food in North America.  They provided an abundant food supply for both the colonists and the First Nations peoples who also used the feathers for adornment.

Turkeys were sold in markets in the east for many years.  In 1711 you could buy one in Hartford, Connecticut for one shilling, four pence.  In 1730 in Northampton, Mass the price was one and one-half pennies per pound.  The last turkey was killed in Massachusetts in 1851 and in Connecticut the last one was seen 1813.  There were very few birds in Kentucky in 1930.  It is estimated the total population got as low as 30,000.  The current population now is estimated to be 7 million.

The Wild Turkey is not mentioned in the 'Birds of New Brunswick:  An Annotated List' (2004).  It has become gradually more populous over the years since it began spreading into New Brunswick from Maine.  The first ones I ever saw in the wild was a flock of about 40 individuals feeding in a field in a hilly area of upper New York State in the winter of 1971.  They had been reintroduced into that state and were expanding at that time.  Although New Brunswick was not normally part of the Wild Turkey range, it has become so with global warming.  We have plenty of good turkey habitat and they are taking advantage of it.  Turkeys prefer hardwood forest especially with nut-bearing fruits (oak) with open areas near water.  They usually roost over or near water.  

                                                         Wild Turkeys Feeding in Our Yard

 Wild Turkeys are large, males are 117 cm (46 inches) long; females, 94 cm (37 inches).  They weigh up to 11 kg (24 lbs).  Some gobblers can get larger that that.  Males have a dark, very iridescent plumage showing beautiful greens and cinnamon browns.  The flight feathers are barred with white and the tail shows barred cinnamon with terminal bands of dark brown and then white.  The head lacks feathers and is red and blue.  He has red wattles and a black tuft of feathers extending from the middle of his breast.  This is about 25 cm (10 in) long but can be up to 45 cm (18 in) long or as short as 8 cm (3 in).  This anatomical feature is known as the 'beard' and is often used to identify males.  It sometimes looks like it is made of hair but it is really modified feathers.  Males also have spurs on their legs.  Females are smaller and duller.  They lack the wattles and usually the beard and spurs.  About 10% of females have beards and sometimes a single small spur but these individuals are normal reproductive females.  Turkey poults have a light cinnamon head, breast and flanks.  The back is heavily spotted with dark browns.  

Male turkeys during breeding season grow a 'breast sponge'.  This is spongiform tissue which swells in the upper breast area near the crop.  It fills with sweet, rich fat which sustains the tom during the breeding season when he is so busy he does not have time to feed.  

The breeding season takes place in the spring.  Turkeys are polygamous and the tom 'services' his harem.  This can be exhausting for him because the hens need to be bred every day when they are laying in order for the eggs to be fertilized.  He has an elaborate courtship display.  He raises and expands his body plumage, spreads his beautiful large tail and his naked head ornaments swell up.  He shakes his adorned head and rattles his wing quills while he drags his wings on the ground while gobbling and strutting around.  Many of us have seen this display and it is remarkable.  

The hen makes her nest on the ground near a tree or log or in some secluded place.  She scratches out a hollow about 30 cm (12 in) wide and 8 cm (3 in) deep and lines it with leaves and dry grasses.  She is careful to keep her nest hidden from the tom.  When all of her 8 to 15 eggs are laid, she incubates them for 28 days.  The precocious young are ready to leave the nest as soon as the last chick is hatched.  The female might bring them back to the nest for a couple of nights after that but they wander thereafter.  The hen is very careful to keep the poults safe and dry.  Predation is common at that time and cold, wet weather causes high mortality.  When the young are about 14 days old they are able to fly into trees to roost in the branches where adult turkeys normally spend their nights.  

It takes 4 years for turkeys to reach full size and colouring.  During the late fall and winter the genders usually flock separately.  Young males often flock separately from the adults toms.  The flock that is currently coming to our yard is mainly females.  Turkeys are non-migratory.  They wander around suitable feeding areas usually near water.  In winter if the snow is very deep and too soft for them to walk easily they will spend considerable time in the trees waiting until conditions improve.  

                                                     Wild Turkeys Feeding in Snow

Domestic turkeys descended from Wild Turkeys.  Turkeys originated in North and Central America.  They were domesticated by the Aztecs about 500 BCE.  The Spanish Conquistadors took them to Europe in the 1500s where they became popular and eventually arrived in England.  The colonists brought the domesticated turkey back to North America.  And, as they say, 'the rest is history'.

New Brunswick has never had a turkey hunting season.  Since the numbers have been increasing hunters have requested from our Department of Natural Resources to instigate a turkey hunting season.  As a result, it has been proposed that open season on turkeys will begin in April, 2021.  From what I understand, hunters will have to apply and have their name drawn.  Hunting will be strictly regulated in specified zones.  It will cost $6 to apply, $20 for the licence and a $5 conservation fee will be added on.  The season will be for 2 weeks beginning on the second Monday in May.  There will be other restrictions as well, e.g., the use of recordings for calling the birds will be prohibited and bearded turkeys only will be 'bagged'.  I expect this new season will cause a lot of opposition.  I wonder if we have a large enough population to begin 'harvesting' (slaughter).  

The Wild Turkey is one of two avian species originating in North America which have been domesticated.  The other is the Muscovy Duck.  Another interesting turkey fact is that it was once considered to be the national bird of the United States, being suggested by Benjamin Franklin.  Maybe they would not have been so slaughtered if they had been the national bird.