Modern Birds

Modern BirdsModern Birds

The other remaining Archosaurs are birds The other remaining Archosaurs are birds given their own class Aves by traditional given their own class Aves by traditional taxonomists.taxonomists.

There are approximately 8,600 species of There are approximately 8,600 species of birds ranging is size from the tiny bee birds ranging is size from the tiny bee hummingbird to the ostrich.hummingbird to the ostrich.

Bee hummingbird http://images.encarta.msn.com/xrefmedia/sharemed/targets/images/pho/t172/T172726A.jpg

http://www.hedweb.com/animimag/ostrich-hotlinks.jpg

Characteristics of the birdsCharacteristics of the birds

Feathers a unique character among living Feathers a unique character among living animals, but also found in dinosaurs.animals, but also found in dinosaurs.

EndothermicEndothermic Skeleton modified for flight. Bones hollow, Skeleton modified for flight. Bones hollow,

forelimbs support the wing, ribs with uncinate forelimbs support the wing, ribs with uncinate processes, beak but no teeth, reduced tail.processes, beak but no teeth, reduced tail.

Breathing by lungs and associated air sacsBreathing by lungs and associated air sacs Internal fertilization and hard-shelled amniotic Internal fertilization and hard-shelled amniotic

eggegg

Evolution of birdsEvolution of birds

Birds evolved from a group of theropod Birds evolved from a group of theropod dinosaurs in the Jurassic period. The oldest dinosaurs in the Jurassic period. The oldest known bird fossil is known bird fossil is Archaeopteryx lithographicaArchaeopteryx lithographica which has a mix of “reptilian” and avian features.which has a mix of “reptilian” and avian features.

Reptilian: long tail, teeth, long clawed fingersReptilian: long tail, teeth, long clawed fingers

Avian: feathers, ribs with uncinate processes, Avian: feathers, ribs with uncinate processes, avian shoulder girdle.avian shoulder girdle.

Archaeopteryx(oldest knownfossil bird)Jurassic 150mya

FeathersFeathers

Among living animals feathers are a Among living animals feathers are a uniquely avian trait.uniquely avian trait.

However, it is now well established that However, it is now well established that feathers also occurred in dinosaurs. In the feathers also occurred in dinosaurs. In the 1990’s feathers were described from 1990’s feathers were described from series of non-avian coelurosaurs, mostly series of non-avian coelurosaurs, mostly from the Chinese Liaoning deposits.from the Chinese Liaoning deposits.

FeathersFeathers

Feathers are what enable birds to fly, but Feathers are what enable birds to fly, but originally are believed to have evolved as originally are believed to have evolved as a thermoregulatory device.a thermoregulatory device.

Feathers are lightweight, but strong. The Feathers are lightweight, but strong. The surface of the feather is made up of tightly surface of the feather is made up of tightly spaced, overlapping filaments that hook spaced, overlapping filaments that hook together. Overlapping feathers form the together. Overlapping feathers form the wings with which birds fly.wings with which birds fly.

Dinosaur feather impressions

Feather structureFeather structure

Feathers are made of keratin: an inert Feathers are made of keratin: an inert substance that consists of insoluble substance that consists of insoluble microscopic filaments embedded in a microscopic filaments embedded in a protein matrix. protein matrix.

Keratin is the substance found in hair, Keratin is the substance found in hair, nails, claws and scales of other animals, nails, claws and scales of other animals, but bird keratin is unique and differs from but bird keratin is unique and differs from that of modern reptiles. that of modern reptiles.

FeathersFeathers

There are two main categories of feathersThere are two main categories of feathers Plumaceous – downy for insulationPlumaceous – downy for insulation Pennaceous – linked , vaned feathers wing and Pennaceous – linked , vaned feathers wing and

contour feathers.contour feathers.

Vane of a typical body feather consists of a Vane of a typical body feather consists of a hidden downy base (for insulation) and an hidden downy base (for insulation) and an exposed cohesive outer portion (for exposed cohesive outer portion (for streamlining). streamlining).

Downy Featherhttp://farm1.static.flickr.com/21/33309716_ad54e344dd.jpg?v=0

FeathersFeathers

Body feathers of most birds include an Body feathers of most birds include an aftershaft that emerges from the underside aftershaft that emerges from the underside of the shaft where the first basal barbs of of the shaft where the first basal barbs of the vane branch off. the vane branch off.

The aftershaft is almost always downy and The aftershaft is almost always downy and functions to increase insulation. In functions to increase insulation. In ptarmigan winter plumage the aftershaft is ptarmigan winter plumage the aftershaft is ¾ as long as the main feather.¾ as long as the main feather.

Aftershafthttp://strategis.ic.gc.ca/pics/cp/feather-e.gif

Ptarmigan:http://fwp.mt.gov/mtoutdoors/images/Portraits/Ptarmigan.jpg

Feather structureFeather structure A contour feather has a long central shaft and a broad flat A contour feather has a long central shaft and a broad flat

vanevane. The hollow base of the shaft (. The hollow base of the shaft (quillquill) anchors the ) anchors the feather in a follicle under the surface of the skin. feather in a follicle under the surface of the skin.

The rest of the shaft, the The rest of the shaft, the rachisrachis, supports the vanes. , supports the vanes. Branching off from the rachis are Branching off from the rachis are barbsbarbs. Each barb has . Each barb has barbules projecting to either side that interlock with the barbules projecting to either side that interlock with the barbules of adjacent barbs.barbules of adjacent barbs.

Barbs and barbules form an interlocking, but flexible Barbs and barbules form an interlocking, but flexible surface. surface.

http://www.birdwatching-bliss.com/bird-feathers.html

19.4

Figure 27.05e

Adaptations for flightAdaptations for flight

In general, the avian skeleton has been In general, the avian skeleton has been lightenedlightened and and strengthenedstrengthened for flight. for flight.

This has been achieved by eliminating This has been achieved by eliminating some structures and modifying others. some structures and modifying others.

Adaptations for flightAdaptations for flight

Feathered wing.Feathered wing. Mass reduction Mass reduction

Wrist bones reduced to two Wrist bones reduced to two Bones hollow and supported by internal struts Bones hollow and supported by internal struts

or spongy bone or spongy bone Reptilian tail lost. Fused tail bones (pygostyle) Reptilian tail lost. Fused tail bones (pygostyle)

support tail featherssupport tail feathers Teeth lost. Skull and bill light but strong.Teeth lost. Skull and bill light but strong.

19.6

Figure 27.08

Adaptations for flightAdaptations for flight Skeleton strengthened Skeleton strengthened

ribs have rear-facing uncinate processes that overlap ribs have rear-facing uncinate processes that overlap and strengthen walls of thoraxand strengthen walls of thorax

bones of wrist, pelvis fused bones of wrist, pelvis fused

Sternum or breastbone enlarged with a large keel (carina) Sternum or breastbone enlarged with a large keel (carina) for attachment of massive flight muscles -- pectoralis and for attachment of massive flight muscles -- pectoralis and supracoracoideus.supracoracoideus.

Fused hand bones support and maneuver primary flight Fused hand bones support and maneuver primary flight feathers. feathers.

Efficient lungs and powerful four-chambered heart power Efficient lungs and powerful four-chambered heart power flight.flight.

Video- skeleton: http://www.birdwatching-bliss.com/bird-skeleton.html

Further skeletal modifications for Further skeletal modifications for flight: Triosseal canalflight: Triosseal canal

TrisossealTrisosseal canalcanal. The triosseal canal is . The triosseal canal is formed by the junction of the coracoid, formed by the junction of the coracoid, scapula and furcula. The supracoracoideus scapula and furcula. The supracoracoideus tendon passes through this canal up from tendon passes through this canal up from the supracoracoideus and inserts on the the supracoracoideus and inserts on the dorsal face of the humerus. dorsal face of the humerus.

Dorsal insertion allows triosseal canal to act Dorsal insertion allows triosseal canal to act as a pulley and the supracoracoideus can as a pulley and the supracoracoideus can lift the wing during the recovery stroke. lift the wing during the recovery stroke.

Triosseal Canal. http://www.palaeos.com/Vertebrates/Units/350Aves/Images/Aves2.gif

Further skeletal modifications for Further skeletal modifications for flight: Triosseal canalflight: Triosseal canal

If the supracoracoideus tendon is cut a If the supracoracoideus tendon is cut a bird cannot takeoff because the bird cannot takeoff because the supracoracoideus muscles are required for supracoracoideus muscles are required for the initial rapid wingbeats necessary to get the initial rapid wingbeats necessary to get a bird off the ground. a bird off the ground.

Once airborne a bird with severed Once airborne a bird with severed supracoracoideus tendons can fly because supracoracoideus tendons can fly because the dorsal elevator muscles are capable of the dorsal elevator muscles are capable of raising the wing on the recovery stroke. raising the wing on the recovery stroke.

Further skeletal modifications for Further skeletal modifications for flightflight

FurculaFurcula The clavicles are fused to form a The clavicles are fused to form a structure called the furcula or wishbone. structure called the furcula or wishbone.

The furcula flexs during flight and spreads The furcula flexs during flight and spreads and contracts during each wingbeat. The and contracts during each wingbeat. The flexing may enhance gas exchange by flexing may enhance gas exchange by assisting in moving air through the air sacs.assisting in moving air through the air sacs.

http://www.birdwatching-bliss.com/bird-http://www.birdwatching-bliss.com/bird-flight.htmlflight.html

Furcula (in red)

http://upload.wikimedia.org/wikipedia/commons/6/6e/Furcula.png

Further skeletal modifications for Further skeletal modifications for flight: arm and fingersflight: arm and fingers

The wing is supported by the The wing is supported by the arm and finger bonesarm and finger bones. There . There are three remaining fingers. The fused hand and finger are three remaining fingers. The fused hand and finger bones provide strength and rigidity in the outer wing bones provide strength and rigidity in the outer wing skeleton. skeleton.

The primary feathers attach to the wrist and finger bones, The primary feathers attach to the wrist and finger bones, while the secondaries attach to the radius and ulna. The while the secondaries attach to the radius and ulna. The first digit (the thumb if birds had one) controls the alula or first digit (the thumb if birds had one) controls the alula or bastard wing. bastard wing.

The alula is a flap that is important in maintaining a smooth The alula is a flap that is important in maintaining a smooth flow of air over the wing at low speeds (it helps prevent flow of air over the wing at low speeds (it helps prevent stalling).stalling).

http://www.dkimages.com/discover/previews/1244/95005058.JPG

Bernoulli’s PrincipleBernoulli’s Principle A bird’s wing is an airfoil and is cambered with a A bird’s wing is an airfoil and is cambered with a

slightly convex upper surface and concave slightly convex upper surface and concave under surface.under surface.

Because air must travel further over the upper Because air must travel further over the upper surface of the wing than below it must travel surface of the wing than below it must travel faster and thus exerts less pressure above the faster and thus exerts less pressure above the wing than it does below. wing than it does below.

The increased pressure below generates lift, the The increased pressure below generates lift, the force which keeps the bird up. force which keeps the bird up.

19.13

Figure 27.16

Lift and thrustLift and thrust In order to fly both horizontal thrust and vertical In order to fly both horizontal thrust and vertical

lift are required.lift are required.

Thrust is mainly generated by the primary Thrust is mainly generated by the primary feathers (the long ones at the end of the bird’s feathers (the long ones at the end of the bird’s hand), which on the downstroke twist and acting hand), which on the downstroke twist and acting like a propeller push the air backwards. like a propeller push the air backwards.

Lift is mainly generated by the secondary Lift is mainly generated by the secondary feathers (the inner portion of the wing), which feathers (the inner portion of the wing), which form an airfoil. form an airfoil.

http://www.birdwatching-bliss.com/bird-flight.htmlhttp://www.birdwatching-bliss.com/bird-flight.html

http://www.dkimages.com/discover/previews/981/50392155.JPG

Arrangement of feathershttp://www.birdsnways.com/wisdom/imgs/wingsm.gif

Structure of hindlimbsStructure of hindlimbs

Legs joints and bonesLegs joints and bones. When looking at . When looking at a birds leg what appears to be the knee is a birds leg what appears to be the knee is not. It is the ankle. not. It is the ankle.

The knee joint is hidden by feathers. The The knee joint is hidden by feathers. The long bone leading from the toes is the long bone leading from the toes is the tarsometatarsus (from tarsals and tarsometatarsus (from tarsals and metatarsals) and above that is the metatarsals) and above that is the tibiotarsustibiotarsus

http://www.palaeos.com/Vertebrates/Lists/Glossary/Images/Hypotarsus.gif

PerchingPerching Being able to perch in trees was an early avian Being able to perch in trees was an early avian

adaptation.adaptation.

The largest group of birds the Passerines The largest group of birds the Passerines (Passeriformes: perching birds) have four (Passeriformes: perching birds) have four moderately long toes, three facing forward and moderately long toes, three facing forward and one back.one back.

The tendons of the toes can lock the foot in a The tendons of the toes can lock the foot in a firm grip. Hence a sleeping bird does not fall off firm grip. Hence a sleeping bird does not fall off its perch.its perch.

Perching Song Thrushhttp://www.bbc.co.uk/cumbria/content/images/2008/02/13/bird_blue_sky_353x470_334x470.jpg

Hopping and walkingHopping and walking

Most passerines hop and in fact most Most passerines hop and in fact most cannot walk. However, some species that cannot walk. However, some species that spend a lot of time on the ground such as spend a lot of time on the ground such as larks and starlings can walk.larks and starlings can walk.

In many other groups of ground-dwelling In many other groups of ground-dwelling birds (e.g. chickens and their relatives) birds (e.g. chickens and their relatives) however walking is used.however walking is used.

RunningRunning

A few birds are specialized for running and A few birds are specialized for running and possess long legs.possess long legs.

The most obvious are the ostrich and The most obvious are the ostrich and relatives. As is the case in horses the relatives. As is the case in horses the number of toes has been reduced to number of toes has been reduced to reduce mass at the end of the limb. reduce mass at the end of the limb. Ostriches have two toes and rheas three.Ostriches have two toes and rheas three.

Ostrich foot: http://lh5.ggpht.com/_jfN-xAu1BR4/Rso0OBjqMjI/AAAAAAAAAS0/jS4eZws8GkY/Zoo+Trip+019.jpg

Climbing Climbing

Various birds including woodpeckers, Various birds including woodpeckers, nuthatches, treecreepers and nuthatches, treecreepers and woodcreepers climb up and down tree woodcreepers climb up and down tree trunks. trunks.

The feet in all cases are strong and the The feet in all cases are strong and the toes usually well curved and the tail is toes usually well curved and the tail is often used as a brace to prop the body often used as a brace to prop the body against the trunk.against the trunk.

Bennett’s Woodpeckerhttp://www.exzooberance.com/virtual%20zoo/they%20fly/woodpecker/Bennetts%20Woodpecker%20268072.jpg

Montane Woodcreeperhttp://www.birdsinperu.com/images/fotos%20aves/Montane-Woodcreeper.jpg

SwimmingSwimming

A wide variety of birds swim and webbing A wide variety of birds swim and webbing of the front three toes has evolved of the front three toes has evolved independently at least four times and all independently at least four times and all four toes are connected by webbing in the four toes are connected by webbing in the pelicans and cormorants.pelicans and cormorants.

The other adaptation to increase surface The other adaptation to increase surface area for swimming is lobed toes.area for swimming is lobed toes.

Pelican Feethttp://farm1.static.flickr.com/179/476653597_bbd825c035.jpg?v=0

Coot Feethttp://jrcompton.com/photos/The_Birds/J/Jan_07/_JR58714-coot-lobed-feet.jpg

Avian lungAvian lung

The metabolic demands of flight are high and to The metabolic demands of flight are high and to meet these demands the avian lung must be meet these demands the avian lung must be much more efficient than the mammalian lung.much more efficient than the mammalian lung.

In birds the finest branches of the bronchi do not In birds the finest branches of the bronchi do not end is saclike alveoli. Instead they form tubelike end is saclike alveoli. Instead they form tubelike parabronchi through which air flows in only one parabronchi through which air flows in only one direction (in contrast to the tidal flow in direction (in contrast to the tidal flow in mammals). Because the air flow is one-way, mammals). Because the air flow is one-way, gases can be more efficiently exchanged and gases can be more efficiently exchanged and there is no “dead air” in the lungsthere is no “dead air” in the lungs

Figure 27.12a

Avian lungsAvian lungs The one-way flow of air is achieved by using a The one-way flow of air is achieved by using a

system of air sacs and a two breath cycle.system of air sacs and a two breath cycle.

On inspiration a bolus of air flows down the On inspiration a bolus of air flows down the trachea to air sacs below the lung. On trachea to air sacs below the lung. On expiration the air mass flows into the lung where expiration the air mass flows into the lung where gas exchange takes place. gas exchange takes place.

With a second inspiration the air mass in the With a second inspiration the air mass in the lung flows into anterior airsacs and with a lung flows into anterior airsacs and with a second expiration exits the body via the trachea. second expiration exits the body via the trachea.

19.10

Figure 27.12b

Feeding and digestion: beaksFeeding and digestion: beaks

Birds are not the only organisms with beaks as Birds are not the only organisms with beaks as turtles and various dinosaurs possessed them turtles and various dinosaurs possessed them too.too.

However, birds have a tremendous diversity of However, birds have a tremendous diversity of beaks. beaks.

The beak is a birds principal tool for handling The beak is a birds principal tool for handling food and its size and shape determine the foods food and its size and shape determine the foods that can be eaten.that can be eaten.

http://www.birdwatching-bliss.com/bird-http://www.birdwatching-bliss.com/bird-beaks.htmlbeaks.html

BeaksBeaks Birds such as crows and ravens have a general purpose Birds such as crows and ravens have a general purpose

bill that can handle lots of different foods.bill that can handle lots of different foods.

Warblers have fine forceps like bills good for handling Warblers have fine forceps like bills good for handling soft-bodied foods such as insects.soft-bodied foods such as insects.

Finches possess short, deep bills that are ideal for Finches possess short, deep bills that are ideal for opening seeds. Crossbills have beaks in which the opening seeds. Crossbills have beaks in which the upper and lower mandibles cross. upper and lower mandibles cross.

These are ideal for opening pine cones to reach the These are ideal for opening pine cones to reach the seedsseeds

Raven:http://www.neothera.com/jpegs/raven.jpg

Magnolia Warbler http://www.hiltonpond.org/images/WarblerMagnoliaM03.jpg

House Finchhttp://www.critterlight.com/House-Finch-6-063003.jpg

Crossbill beakhttp://newsimg.bbc.co.uk/media/images/41436000/jpg/_41436817_malecrossbill203rspb.jpg

BeaksBeaks

Dabbling ducks, such as mallards, have Dabbling ducks, such as mallards, have beaks that are good for straining water. beaks that are good for straining water. However, ducks such as mergansers have However, ducks such as mergansers have beaks that are serrated and help in beaks that are serrated and help in grasping fish.grasping fish.

Spoonbills and flamingoes possess bills Spoonbills and flamingoes possess bills similar to dabbling ducks that are good for similar to dabbling ducks that are good for sifting mud and water.sifting mud and water.

Merganser beakhttp://www.learner.org/jnorth/images/graphics/a-b/Beak-Merganser.jpg

Common Merganser:http://library.thinkquest.org/TQ0310822/images/Common_merganser.jpg

Flamingo beakhttp://spot.colorado.edu/~humphrey/fact%20sheets/flamingo_caribbean/images/flamingo_head.gif

BeaksBeaks

Raptors, such as owls, hawks and eagles, Raptors, such as owls, hawks and eagles, possess short bills with a hooked tip that possess short bills with a hooked tip that are ideal for dismembering prey.are ideal for dismembering prey.

Ferrunginous Hawkhttp://www.photographytips.com/images/rhonda-spencer-ferruginous-hawk.jpg

BeaksBeaks

Toucans and hornbills are both fruit Toucans and hornbills are both fruit specialists and their light, but long bills specialists and their light, but long bills allow them to pluck distant fruit.allow them to pluck distant fruit.

Keel-billed Toucanhttp://www.sottm.com/Toucan.jpg

Great Hornbill:http://khaoyai.files.wordpress.com/2008/01/hornbill_013.jpg

BeaksBeaks

Among the more unusual beaks is the Among the more unusual beaks is the beak of the skimmer a relative of the gulls beak of the skimmer a relative of the gulls and terns.and terns.

In skimmers the lower mandible is laterally In skimmers the lower mandible is laterally compressed and the bird flies over the compressed and the bird flies over the water with the lower mandible skimming water with the lower mandible skimming through the water. When the beak hits a through the water. When the beak hits a fish, it snaps shut immediately on it.fish, it snaps shut immediately on it.

Black Skimmerhttp://i.pbase.com/v3/88/57088/1/46667287.black_skimmer.jpg

Feeding and digestionFeeding and digestion Because birds lack teeth they can’t process food Because birds lack teeth they can’t process food

much in the mouth so that is left up to the gastric much in the mouth so that is left up to the gastric system.system.

Birds can frequently gather food faster than it Birds can frequently gather food faster than it can be processed. This food is usually stored in can be processed. This food is usually stored in the birds crop, an enlarged part of the the birds crop, an enlarged part of the esophagus. esophagus.

The crop is also used to store food that will later The crop is also used to store food that will later be regurgitated to chicks.be regurgitated to chicks.

Bird’s digestive tract and other internal organshttp://www.dkimages.com/discover/previews/824/80016755.JPG

HoatzinHoatzin

One South American bird, the Hoatzin is One South American bird, the Hoatzin is an obligate leaf eater and this is the only an obligate leaf eater and this is the only bird that uses its crop as a fermentation bird that uses its crop as a fermentation chamber.chamber.

Hoatzins are also unusual because their Hoatzins are also unusual because their chicks possess claws on their wings, chicks possess claws on their wings, which they use to scramble around in the which they use to scramble around in the branches. The claws are later lost.branches. The claws are later lost.

Adult Hoatzinhttp://www.rarespecies.org/hoatzin.jpg

http://3.bp.blogspot.com/_E87qS3OzVLQ/SdP3gaOsBZI/AAAAAAAAD3E/3fjXx4nJ4ak/s200/Hoatzin_chick_w_claws.jpg

StomachStomach

The stomach a birds possesses is dictated The stomach a birds possesses is dictated by its diet. Birds that each high volumes by its diet. Birds that each high volumes of soft foods such as meat have extensible of soft foods such as meat have extensible stomachs that can hold a lot of food.stomachs that can hold a lot of food.

Those that have to process tough foods Those that have to process tough foods such as seeds and insects have much such as seeds and insects have much more muscular stomachs that help to grind more muscular stomachs that help to grind the food.the food.

StomachStomach

A bird’s stomach has two parts the anterior A bird’s stomach has two parts the anterior glandular proventriculus and the posterior glandular proventriculus and the posterior gizzard. gizzard.

The proventriculus contains glands that The proventriculus contains glands that secrete digestive enzymes. In birds that secrete digestive enzymes. In birds that swallow whole foods such as fruits the swallow whole foods such as fruits the proventriculus is often very large.proventriculus is often very large.

GizzardGizzard

The gizzard’s main function is to The gizzard’s main function is to mechanically process food. mechanically process food.

The walls of the gizzard are thick and The walls of the gizzard are thick and muscular and the gizzard often contains muscular and the gizzard often contains small stones, which the birds swallow to small stones, which the birds swallow to assist in grinding the food. The gizzard assist in grinding the food. The gizzard thus fulfills the same role as the teeth in thus fulfills the same role as the teeth in mammals.mammals.

GizzardGizzard

The gizzard can exert significant pressure. The gizzard can exert significant pressure. For example, a turkey’s gizzard can For example, a turkey’s gizzard can process two dozen walnuts in about four process two dozen walnuts in about four hours. hours.

It can also crack hickory nuts, which It can also crack hickory nuts, which require 50-150kg of pressure to break.require 50-150kg of pressure to break.

IntestinesIntestines

The main site of chemical digestion is the The main site of chemical digestion is the intestine where enzymes break down the intestine where enzymes break down the food into small molecules that can be food into small molecules that can be absorbed across the intestinal wall.absorbed across the intestinal wall.

Seasonal changes in gut Seasonal changes in gut morphologymorphology

Birds often change their diets over the course of a year Birds often change their diets over the course of a year and gut morphology changes too. Insects are more and gut morphology changes too. Insects are more easily and quickly digested than plant food (e.g. berries). easily and quickly digested than plant food (e.g. berries).

When starlings switch to eating more plant material in When starlings switch to eating more plant material in the fall their intestines increase in length by about 20% the fall their intestines increase in length by about 20% and decrease by a similar amount in spring when their and decrease by a similar amount in spring when their diet switches back to animal prey.diet switches back to animal prey.

Accompanying the morphological changes are changes Accompanying the morphological changes are changes in the types and quantities of digestive enzymes in the types and quantities of digestive enzymes produced tailored to match the composition of the diet.produced tailored to match the composition of the diet.

Sensory systems: visionSensory systems: vision

Most birds have excellent vision and this is Most birds have excellent vision and this is reflected in the structure of the brain. reflected in the structure of the brain. There are large optic lobes and the There are large optic lobes and the midbrain which processes visual midbrain which processes visual information is enlarged.information is enlarged.

In contrast, in most birds olfaction is In contrast, in most birds olfaction is unimportant and the olfactory bulbs are unimportant and the olfactory bulbs are small.small.

Puerto Rican Screech owlhttp://www.fs.fed.us/r8/caribbean/wildlife-facts/2003/wildlife-facts_images_2003/pr_screech_owl.jpg

VisionVision Birds have very large eyes so much so that the brain is Birds have very large eyes so much so that the brain is

up and back in the skull to accommodate them.up and back in the skull to accommodate them.

Bird eyes are similar in structure to those of other Bird eyes are similar in structure to those of other vertebrates, but the shape varies from a flattened sphere vertebrates, but the shape varies from a flattened sphere to tube-like. to tube-like.

The variation is shape appears to be a result of the The variation is shape appears to be a result of the difficulties of fitting an enlarged eye into a more modest difficulties of fitting an enlarged eye into a more modest sized skull. By altering eye shape birds such as owls sized skull. By altering eye shape birds such as owls have avoided developing the disproportionately large have avoided developing the disproportionately large heads they would have required if the eye were heads they would have required if the eye were spherical.spherical.

A unique feature of the avian eye is the presence of a A unique feature of the avian eye is the presence of a comb-like structure called the pecten.comb-like structure called the pecten.

The pecten arises from the rear of the eye close to The pecten arises from the rear of the eye close to where the optic nerve exits the eye. where the optic nerve exits the eye.

The function of the pecten remains unclear even after The function of the pecten remains unclear even after 200 years of investigation. The organ’s large blood 200 years of investigation. The organ’s large blood supply suggests it may provide nutrition to the retina and supply suggests it may provide nutrition to the retina and perhaps remove metabolic wastes from the vitreous perhaps remove metabolic wastes from the vitreous humor.humor.

VisionVision

A second interesting feature of avian eyes A second interesting feature of avian eyes is the presence of colored oil droplets in is the presence of colored oil droplets in cone cells.cone cells.

These act as filters absorbing certain These act as filters absorbing certain wavelengths of light and allowing others wavelengths of light and allowing others through, but their exact function remains through, but their exact function remains unclear.unclear.

HearingHearing

Birds have hearing that is comparable in Birds have hearing that is comparable in sensitivity to that of humans even though their sensitivity to that of humans even though their heads are much smaller.heads are much smaller.

However, they have proportionally much larger However, they have proportionally much larger tympanic membranes which enhances sensitivity tympanic membranes which enhances sensitivity to sound. In addition, the cochlea has about 10x to sound. In addition, the cochlea has about 10x as many hair cells per unit length than a as many hair cells per unit length than a mammalian cochlea does.mammalian cochlea does.

HearingHearing

Owls possess the most acute hearing among Owls possess the most acute hearing among birds (comparable to that of a cat) and can birds (comparable to that of a cat) and can isolate sounds very accurately even in complete isolate sounds very accurately even in complete darkness.darkness.

Owls possess a distinctive facial ruff of stiff Owls possess a distinctive facial ruff of stiff feathers that acts as a parabolic sound reflector, feathers that acts as a parabolic sound reflector, which focuses and amplifies sounds.which focuses and amplifies sounds.

Some ruffs are asymmetric and the ruff’s Some ruffs are asymmetric and the ruff’s asymmetry (as well as asymmetry in the vertical asymmetry (as well as asymmetry in the vertical placement of the ears) enhances the owls ability placement of the ears) enhances the owls ability to isolate sounds in three dimensional space.to isolate sounds in three dimensional space.

Barn owlhttp://www.usbr.gov/mp/ccao/newmelones/images/wildlife_barn_owl.jpg

HearingHearing

The asymmetries in the ruff and ears cause The asymmetries in the ruff and ears cause delays in the time at which sounds reach each delays in the time at which sounds reach each ear that can be interpreted by the brain and ear that can be interpreted by the brain and used to identify precisely the source of a sound.used to identify precisely the source of a sound.

A barn owl’s ability to do this is so good that it A barn owl’s ability to do this is so good that it can isolate sound to within 1can isolate sound to within 1º in three º in three dimensional space. If you envisioned yourself dimensional space. If you envisioned yourself surrounded by a sphere with a radius surrounded by a sphere with a radius approximately equal to your arm length 1º would approximately equal to your arm length 1º would be about the area covered by a fingertip.be about the area covered by a fingertip.

OlfactionOlfaction

Most birds have a poorly developed sense Most birds have a poorly developed sense of smell, but a few groups do have a good of smell, but a few groups do have a good sense of smell. sense of smell.

These include kiwis which have their These include kiwis which have their nostrils at the end of the bill and use odor nostrils at the end of the bill and use odor cues to find prey when they probe in the cues to find prey when they probe in the earth. earth.

Brown Kiwi hatched at the Smithsonina National Zoo 2006:http://news.nationalgeographic.com/news/2006/02/images/060217_kiwi.jpg

OlfactionOlfaction

Other birds with a good sense of smell are Other birds with a good sense of smell are the various “tubenoses” the petrels, the various “tubenoses” the petrels, shearwaters and albatrosses, which are shearwaters and albatrosses, which are attracted to the scent of chummed fish and attracted to the scent of chummed fish and fish from a considerable distance.fish from a considerable distance.

In addition, turkey vultures have a well In addition, turkey vultures have a well developed sense of smell and can find developed sense of smell and can find even covered carcasses very quickly.even covered carcasses very quickly.

http://www.wildland.com/trips/details/Images/anf_albatross_b.jpg

Turkey Vulture: http://www.lakesidenaturecenter.org/images/AC_Turkey%20Vulture%20Head%20Shot%20from%20MDC.jpg

Diversity of birds: major bird ordersDiversity of birds: major bird orders

Struthioniformes: Ostriches, rheas, Struthioniformes: Ostriches, rheas, cassowariescassowaries

Podicipediformes – Grebes (diving birds Podicipediformes – Grebes (diving birds with lobed feet). 21 species. with lobed feet). 21 species.

Gaviiformes – Loons. 5 species.Gaviiformes – Loons. 5 species. Pelecaniformes. Pelicans and Pelecaniformes. Pelicans and

cormorants. 67 species.cormorants. 67 species.

Southern Cassowaryhttp://www.daintreebirdwatching.com.au/images/cassowary-Robert%20South3.jpg

Pied-billed Grebehttp://www.geometer.org/TT2004/Florida/images/Grebe.jpg

Common Loonhttp://www.freewebs.com/swiv/common-loon.jpg

Great Cormoranthttp://www.kenyabirds.org.uk/pics/great_cormorant.jpg


Anseriformes – Waterfowl. Ducks, geese Anseriformes – Waterfowl. Ducks, geese and swans. About 160 species.and swans. About 160 species.

Falconiformes Hawks, eagles and falcons. Falconiformes Hawks, eagles and falcons. Over 300 species Over 300 species

Galliformes – chicken-like birds. Grouse, Galliformes – chicken-like birds. Grouse, quail, turkeys. Over 250 species.quail, turkeys. Over 250 species.

Ruffed Grousehttp://sdakotabirds.com/species/photos/ruffed_grouse.jpg


Ciconiiformes – Long-legged wading birds. Ciconiiformes – Long-legged wading birds. Storks, herons, ibises, egrets. 120 species.Storks, herons, ibises, egrets. 120 species.

Charadriiformes – Shorebirds and gulls. Charadriiformes – Shorebirds and gulls. Plovers, sandpipers, stilts, auk, puffins, gulls and Plovers, sandpipers, stilts, auk, puffins, gulls and terns. Over 360 species.terns. Over 360 species.

Columbiformes – Pigeons and doves. Over 300 Columbiformes – Pigeons and doves. Over 300 species.species.

Psittaciformes Parrots. More than 350 speciesPsittaciformes Parrots. More than 350 species

White Storkhttp://susty.com/image/stork-long-orange-legs-beak-white-feathers-black-plumage-stand-sleeping-green-vegetation-photo.jpg

Razorbill (auk)http://media-2.web.britannica.com/eb-media/16/26016-004-13D8FA4C.jpg

Rock Dovehttp://www.astro.umd.edu/~dcr/Archives/Photos/Birds/filenames/Pigeon,Feral.jpg

http://creagrus.home.montereybay.com/Parrot-BN_MR7817-w.jpg

Scarlet Macawhttp://animalsneedkisses.files.wordpress.com/2009/03/parrot.jpg


Strigiformes – Owls. About 180 species.Strigiformes – Owls. About 180 species. Apodiformes – Short-legged acrobatic Apodiformes – Short-legged acrobatic

fliers. Swifts and hummingbirds. About fliers. Swifts and hummingbirds. About 420 species.420 species.

Piciformes – Woodpeckers. About 400 Piciformes – Woodpeckers. About 400 species.species.

Common Swifthttp://www.naturephoto-cz.com/photos/birds/common-swift-3629.jpg


Passeriformes – Perching birds. Passeriformes – Perching birds. Songbirds. Crows, warblers, cardinals, Songbirds. Crows, warblers, cardinals, sparrows, starlings, etc. Over 5,700 sparrows, starlings, etc. Over 5,700 species.species.

European Starlinghttp://rightofmiddle.files.wordpress.com/2009/01/european-starling.jpg

Cardinalhttp://2.bp.blogspot.com/_-cBb578jsLk/RmP1nuxW8II/AAAAAAAAAHM/SCIyggloewY/s400/cardinal.jpg