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Questions and Answers
What is the primary function of the uropygial gland in birds?
Which component of feathers is responsible for interlocking adjacent barbs to maintain feather structure?
What is the purpose of smooth muscles in relation to feathers?
What distinguishes claws of birds of prey (BOP) from other types of claws?
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What are apteria in birds?
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What is the function of the syrinx in birds?
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How does the digestive system of birds differ from that of humans?
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What role do air sacs play in the avian respiratory system?
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What component of the female reproductive tract secretes the layers of albumin for eggs?
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Which of the following sensory nerve endings is primarily used for protection in birds?
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What is the purpose of the renal portal system in birds?
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What is true about the composition of bird urine?
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How do nocturnal species primarily rely on their sensory systems?
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What is the primary function of the proventriculus in birds?
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What is the significance of the unidirectional airflow in avian lungs?
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What is the primary energy requirement for the molting process?
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Which type of muscle is primarily responsible for the downstroke of a bird's wing during flight?
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What modification helps reduce the weight of a bird's skeleton for flight?
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In diurnal birds, what is the typical shape of the eye?
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What structure in the bird's eye is responsible for lubricating and protecting the eye?
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Which muscle group makes up 20%-25% of the body weight in long-distance flying birds?
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What is the purpose of the pecton within a bird's eye?
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How does the structure of a bird's middle ear differ from that of mammals?
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Which feature of the sternum is crucial for the origin of flight muscles in birds?
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What is a major feature of the skeletal adaptation in birds that supports their ability to fly?
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Study Notes
Skin
- Epidermis is thin, contains keratin, produces scales, feathers, beak sheaths, and claws.
- Dermis is thicker, but still thin, contains fat for insulation and nutrition.
- Smooth muscles attached to feather follicles allow for thermoregulation:
- Puffing up traps heat.
- Flattening against the body promotes heat loss.
Uropygial Gland
- Also known as the "preen gland".
- Located on the dorsal surface at the upper base of the tail.
- Secretes an oily/fatty substance.
- Used for cleaning feathers and waterproofing.
- Larger in aquatic/tropical species.
- Absent in ostriches, some psittacines, and a few other species.
Claws and Beak
- The beak is a tough, horny epidermal covering that grows continuously.
- Beak size, shape, and hardness vary depending on their function.
- Claws come in different types depending on the bird's habits.
- Birds of Prey have talons.
Feathers
- Outgrowths of skin, made of protein, and non-living structures.
- Feathers compose 4-12% of a bird's body weight.
- Only the base of feathers has sensation.
- Enable flight, protection, thermoregulation, camouflage, and communication behaviors.
- Different feather types have different functions.
Feather Anatomy
- Rachis: Main feather shaft.
- Inferior Umbilicus: Opening at the base of the feather.
- Superior Umbilicus: Openings on the shaft where the webbed part begins.
- Calamus: Hollow part extending from the inferior to superior umbilicus.
Feather Anatomy
- Vane: Flattened, web-like part of the feather.
- Barbs: Projections that comprise a vein.
- Barbules: Microscopic projections that maintain feather structure.
- Hamuli: Hooklets that interlock barbs with adjacent ones, forming a flexible web.
Feather Growth
- Feathers originate from seven tracts called pterylae.
- Apteria are bare areas of skin.
- Fault bars (stress bars): A weakened area on the vane that lacks barbules.
- Caused by stress during development, the rachis is pinched, depleting blood supply.
- Blood supply returns when the stressor is removed.
- Nutrition is the most common cause.
Molting
- Process of feather replacement, requires a large amount of energy.
- Occurs one to several times per year.
- Molting feathers develop from papillae in the dermis and contain germ cells.
- Activated by physiological and environmental factors.
- Newly developed feathers push out old feathers.
Molting
- The new feather is covered by periderm- an epidermal covering, removed by preening.
- Blood vessels reach into the new feather.
- When the feather is fully developed, blood dries up, and the rachis is pinched.
Muscles
- Special muscles have developed for flying, most are placed ventrally.
- 175-200 muscles.
- White muscles: Thick, low blood supply, and little myoglobin. Used for short-distance flyers.
- Red Muscles: Thinner, rich blood supply, fat, myoglobin, and mitochondria. Used for long-distance flyers.
Muscles
- Pectoralis (breast muscle): Inserts in the underside of the humerus.
- Compression causes a depression of the wing.
- Common place for IM injections.
Muscles
- Supracoracoideus: Turns into a tendon that passes through the cavity formed by the shoulder girdle and inserts in the top of the humerus.
- Counteraction (upstroke of the wing).
- In long-distance fliers, these two muscles comprise 20-25% of body weight.
Muscles
- Muscles of the femur control movement in the distal leg and toes via tendons.
- Perching reflex: When legs bend to perch, tendons bend and pull toes closed around the perch.
- May also be used for predation.
Skeleton
- Must support flight and walking.
- Modifications to support flight:
- Reduction in the number of bones.
- Fusion of bones to form plates that provide strength and simplify movements.
- Reduction in density, strengthened by a network of internal bony braces.
- Loss of internal bone matrix.
Bones - Skull
- Large portion of the skull is devoted to protecting the eyes.
- Sclerotic ring: A ring of protective bony plates surrounding the eyes.
Bones - Sternum
- Large and concave, the place of origin for flight muscles.
- Keel: Large bony ridge.
- Lacking in flightless birds.
- Large in long-distance fliers.
- Smaller in short-distance fliers.
Bones - Wings
- Long in birds that glide or soar.
- Shorter in birds that flap.
- The ulna has a larger diameter than the radius.
Sense Organs - Vision
- Good vision is essential for avian life.
- The optic lobe takes up most of the midbrain.
- Eye shapes: Round, flat, or tubular.
- Diurnal birds: Round/relatively flat.
- Nocturnal birds: Tubular with large pupils.
Vision
- Nictitating membrane: Lubricates and protects the eyes, voluntary control (striated muscles).
- Iris: Striated muscles, PLR’s are not a good diagnostic tool in birds.
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Pecton: In the vitreous humor, distributes nutrition, ribbon-like structure- very vascular.
- 30% of traumatized birds suffer hemorrhage from the pecton.
Photoreception
- The retina is only slightly vascularized. This decreases interruption of the image.
- 1.5-2 times the amount of photoreceptors than any other vertebrate.
- Each cone is attached to a single nerve fiber.
- Some birds have 2 fovea- funnel-shaped areas with high concentrations of cones.
- Color vision is not completely understood.
- Some birds can detect UV light (diurnal species).
Hearing
- Structure is simpler than in mammals.
- The middle ear contains a single bone, the columella, which connects to the inner ear. It functions as a funnel for sound.
- Nocturnal species rely on hearing for predation.
Taste
- Contains only 50-400 taste buds (humans have 10,000).
- Located on the side of the tongue and soft palate.
- Sensitivities and thresholds are specific to each species.
Touch
- Birds have two types of sensory nerve endings, used mainly for finding food and protection.
- Grandry’s corpuscle: Tongue and palate.
- Herbst corpuscle: Tongue, palate, beak, cloaca, legs, wings, uropygial gland, and bases of many feathers.
- Auriculars: Contour feathers around the ears.
Smell
- Smell varies widely between species.
- In some species, smell is highly developed.
- Used for finding food and reproduction.
Digestive System
- Birds have a fast metabolism and high energy demand.
- They assimilate 60-99% of the energy consumed.
Digestive System
- Bill: Size and shape vary with diet.
- Mouth: Psittacines have a very muscular tongue.
-
Esophagus: Right side of the neck.
-
Crop: Storage pouch for food.
- Single or double-pouched. Birds with a well-developed crop eat few larger meals. Birds with small crops forage all day.
- Regulates the passage of food.
-
Crop: Storage pouch for food.
Stomach
- Proventriculus: Anterior chamber, chemical digestion.
- Ventriculus (gizzard): Grinds food components.
- Indigestible food is regurgitated as pellets.
Digestive System
- Liver: Bilobed, the right lobe is larger than the left.
- Pancreas: Relatively large, larger in fish/grain eaters.
-
Cloaca:
- Coprodeum: Fecal matter.
- Urodeum: Discharge from kidneys/genital duct.
- Proctodeum: Stores excrement.
Circulatory System
-
Blood:
- Nucleated red blood cells, oval shaped.
- Heterophils = neutrophils.
- Passerines: Blood formed in the spleen and liver.
Circulatory System
-
Renal portal system:
- Blood returning from the iliac veins travels to the kidneys.
- Valves at the junction of the iliac and renal veins steer blood to the kidneys or to the heart via the posterior vena cava.
Respiratory System
- Choanae: Internal nares open from the nasal cavity to the roof of the mouth.
- Syrinx: Enlargement of the trachea cranial to the sternum (voice box).
- Trachea: Complete tracheal rings.
- Bronchi: Extend to air sacs.
- Mesobronchi: Once inside the lungs.
Respiratory System
- Ventrobronchi: Four sets, supplying different parts of the lung with air.
- Parabronchi: Connected to air capillaries, gas exchange occurs here.
Air Sacs
- Two cranial thoracic, two caudal thoracic, two cervical, two abdominal, and one interclavicular.
- Reservoirs for air.
- Provide warmth and moisture to facilitate diffusion (gas exchange).
- Thermoregulate (internal evaporative cooling).
- Provide buoyancy.
Lungs
- Small and attached to thoracic vertebrae and ribs.
- Bright red, highly vascularized, and inelastic.
- Unidirectional airway.
Respiratory Cycle
- First inhalation: Expansion of the coelomic cavity creates a pressure gradient. Air flows to the posterior air sacs.
- First exhalation: Air is pushed into the lungs, gas exchange occurs.
- Second inhalation: From the lungs and into anterior air sacs.
- Second exhalation: Air leaves the body through the trachea.
Respiratory Cycle
- Fresh air flows in a continuous unidirectional path within the lungs.
- There is no mixed air or residual air.
Urogenital - Kidneys
- Elongated and do not contain a renal pelvis.
- Urine composition: 75% uric acid (white stuff) - urates.
- More efficient in eliminating nitrogen.
- Conserves water.
- Survival of embryos: Less water to store.
Male Reproductive Tract
- Gonads enlarge during the breeding season.
- Bean-shaped.
- Psittacines: Sperm is passed to the vagina via contact with the female cloacae.
Female Reproductive Tract
- The oviduct comprises five sections:
- Infundibulum: Grabs the ovum as it comes out of the ovary.
- Magnum: Secretes layers of albumin (egg whites).
- Isthmus: Deposits keratin shell membrane.
- Uterus (shell gland): Deposits water, albumin, a hard external shell, and pigmentation.
- Vagina: Secretes mucous for oviposition and can store sperm for hours to days.
Females cont.
- Oviposition (laying an egg) occurs when the egg gets to the cloaca.
- Cloaca is a common opening for the urinary, digestive, and reproductive tracts just like in reptiles.
- Females have two ovaries, but only the left is functional. Ovaries contain follicles, which produce the yolk of the egg.
- Ovaries also produce estrogen, progesterone, and testosterone.
- Birds cannot survive with just one ovary or just one oviduct.
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Description
This quiz covers the anatomy of birds, with a focus on their skin, uropygial gland, claws, beak, and feathers. Learn about the structure and functions of these features, including how they help with thermoregulation and waterproofing in various species. Ideal for students studying avian biology.
