Avian Anatomy: Combs and Feathers

External Anatomy of Avian Species

• Beak is a hard structure that surrounds the mouth
• Comb is a fleshy growth on the top of the head of chickens
• There are 8 varieties of combs

Varieties of Comb

• Buttercup combs are cup-shaped, centered on the head, with evenly spaced points
• Cushion combs are small and close to the head, lacking spikes, bumps, or other irregularities
• Pea combs are fairly close to the head and have 3 ridges along their length
• Rose combs are wide, fleshy, low to the head, and have a flat top ending in a spike
• Silkie combs are round and lumpy, wider than other combs, and often seen in crested birds
• Single combs are single blade-shaped, centered, and possess 5-6 defined points
• Strawberry combs are egg-shaped and set close to the head
• V-shaped combs have 2 hornlike sections joining to form a V shape

Feathers

• Feathers are the outer covering of avian species
• Made of protein and protect the body from the elements

Varieties of Feathers

• Contour feathers cover the body of the bird
• Coverts are feathers on the wings that cover the bases of the primary and secondary feathers
• Down feathers are small, soft, and close to the body, present on young birds
• Hackles are long, slender feathers on the neck of some birds
• Primary feathers are large and found on the end of the wings
• Secondary feathers are large, stiff, and located on the portion of the wing near a bird's body

Feather Patterns

• Barred feathers have alternating stripes of different colors across the width

• Laced feathers have a narrow border of contrasting color

• Mottled feathers have tips that are white, differing from spangling where not all feathers are tipped

• Pencilled feathers have narrow, uniform lines of contrasting colors and may be single or multiple

• Spangled feathers have a contrasting color at the tip, black or white

• Differ from mottled feathers, spangling occurs on every feather

Feather Functions

• Flight capabilities
• Protect thin skin from trauma, rain, and excessive radiation
• Assist in thermoregulation and camouflage
• Used in communication behaviors

Feather Structure

• Inferior Umbilicus: an opening at the base of the feather
• Superior Umbilicus: an opening on the feather shaft from where the webbed part begins
• Afterfeather: A type of accessory feather that provides insulation
• Calamus: the quill, round, hollow, and semitransparent
• Extends from the inferior to superior umbilicus
• Rachis is the main feather shaft
• Vane is the flattened part
• Contains closely spaced barbs that give rise to barbules containing hooklets (hamuli)
• Hooklets interlock each barb with an adjacent one

Types of Feathers

• Contour Feathers: flight feathers of the wing & tail

• Moved by muscles attached to the walls of the follicles

• Auriculars: Small contour feathers around ear openings improve hearing

• Semiplume Feathers: main rachis with barbs and no barbules/hooklets; provide insulation and flexibility

• Down Feathers: soft, fluffy, lack a true shaft; used for insulation

• Filoplume Feathers: bare shaft with barbs on the tip; may control feather movement

• Bristles: modified contour feather with a stiff rachis and few barbs; may play a role in the sense of touch

• Powder Down Feathers: grow continuously at the base, disintegrate at the tip, birds create waxy powder that spreads throughout the plumage, birds without an uropygial gland have abundant powder down feather

Feathers

• Pterylae: tracts where feathers are located
• Apteria: bare areas of skin between pterylae

External Anatomy

• Saddle: Caudal portion of a topline of bird
• Shank: Leg of the chicken between the hock & foot
• Spurs: sharp, bony projection from the shank of poultry
• Wattle: flesh tissue located near the chin that dangles down below the head
• Epidermis: thin layer of flattened epithelial cells that produce keratin for scales, feathers, beaks, & claws
• Dermis: thick layer of fibrous connective tissue

Avian Glands

• Fat is stored for nutrition and insulation
• Smooth muscles are used in dermis innervate feather follicles to aid in heat regulation
• Uropygial (preen) Gland located on the dorsal surface at the tail base
• Preening stimulates oily secretion
• Birds use their beaks to spread oil throughout the feathers to clean and waterproof them

Beak

• Derivative of skin
• Upper and lower mandible covered with a horny keratin layer
• Grows continuously
• Variable hardness and flexibility

Claws

• Horny sheath derived from specialized scales at the end of each toe
• Grows continuously
• Variable types of claws, depending on perching and procuring food

Skeletal System

• Skulls are thin
• Jaws extend into a keratinized bill
• Large eye sockets bordered by sclerotic ring

Vertebral Column

• Cervical Vertebrae: The atlas contains a single condyle for attachment of the skull, allowing greater range of head movements
• Thoracic Vertebrae: They are rigid and proved a strong support for the rib cage
• Lumbar & Sacral Vertebrae fused to form the Synsacrum
• Coccygeal Vertebrae: The first few are mobile

Synsacrum & Pygostyle

• Synsacrum: a strong bony plate created by fusion of distal lumbar, sacral, and coccygeal vertebrae
• Fuses with the pelvis and supports the legs
• Pygostyle: Created from fusion of some coccygeal vertebrae

Sternum & Girdles

• Sternum: large & concave, it is the origin for flight muscles; lacks a keel in flightless birds
• Pectoral Girdle: paired coracoids, scapulas, & clavicles
• Pelvic Girdle: 3 paired bones joining where the leg attaches to the body

Wing Structure

• Glenoid Cavity: formed from scapula & coracoid; site of wing joint attachment
• Clavicles (wishbone): positioned outward & forward

Wing

• Wings: joint at shoulder allows rotation in several planes
• Humerus: wing muscle attach at the pectoral crest, joint at elbow only allows movement parallel to wing
• Ulna: has a larger diameter than radius
• Patagium: ligament along cranial edge, elasticity in the wings and assisting in flight aerodynamics
• Alula: originates from the wrist and carries feathers
• Metacarpal: joins with the 2nd & 3rd fingers near the distal end of the wing and helps support the primary flight feathers
• Ileum: Broad and fused to the synsacrum
• Ischium & Pubis: thin, long, & fused to the ileum anteriorly

Feet

• Metatarsal pad is the bottom of the foot surrounded by 2, 3, or 4 toes
• Bird feet have different toe arrangements
• Anisodactyl: 1 toe faces the rear, other 3 face forward
• Zygodactyl: 2nd & 3rd toes face forward, 1st & 4th are directed backward
• Digits are numbered
• Digit 1: 1 joint, Digit 2: 2 joints, Digit 3: 3 joints, Digit 4: 4 joints

Muscles

• Skeletal Muscles: can have white or red muscle fibers or a combination
• White Fibers: thick in diameter, low blood supply, little myoglobin
• Red Fibers: thin, have a rich supply of blood, fat, myoglobin, & mitochondria
• Wing Muscles can raise or depress leading edge of wing and pull extend or flex the wing

Flight Muscles

• Pectoralis:
  • Large, superficial
  • Origin: Sternum
  • Insertion: Underside of humerus
  • Depresses wing during downstroke
• Supracoracoideus:
  • Small, deeper
  • Origin: Sternum
  • Insertion: Top of humerus
  • Elevates wing, performing upstroke

Avian Senses & Neurology

• Leg Muscles: located over femur and are a small number located over the tibiotarsus & tarsometatarsus

• Muscles of Head & Neck: the extent of jaw muscles varies depending on bird feeding habits and neck muscles allow movement in different directions

• Sense Organs: the location of control centers of brain are similar to mammals and control centers for vision & hearing are large and control centers for taste, touch, & smell are small

• Optic Lobes make up the majority of their midbrain

• Eye shape is determined by orbits

• Diurnal Birds: have round/flat eyes

• Nocturnal Species: have tubular eyes

Avian Eyes

• Fibrous Tunic: comprised of the sclera and cornea
• Sclera contains a ring of bones also known as the sclerotic ring.
• Uveal Tunic: choroid, iris, ciliary muscles
• Nictitating Membrane: may have a clear center
• Neural Tunic: consists of the retina

Eye Anatomy

• Pectin is the vascular structure attached to the retina
• There is photoreception
• Rods and cones similar to mammals
• Nocturnal birds have more rods than cones
• Rods contain rhodopsin (pigment) for night vision
• Retina is lightly vascularized with many photoreceptor cells

Ear

• External Ear is often bordered with auricular feathers

• Hearing in Nocturnal Owls - Hearing in Nocturnal Owls

• Operculum: fleshy flap of skin at external ear opening; helps funnel sound into ears

• Ear openings are typically assymetrical and also helps with vertical location of sound

Additional Avian Sensory Organs

• Taste Buds: few in number, on the sides of the tongue & soft palate
• Nerve Endings are for touch.
• Grandry’s Corpuscle is in the tongue & palate of species that dig for food.
• Herbist Corpuscle is sensitive to feather movement.

Additional Information

• Smell - is variable
• Endocrine System - has 7 major endocrine glands.
• Digestive System - they also have a digestive system
• Columella single bone in middle ear
• Birds can see a wide array of wavelengths

Digestion

• Beaks - vary based on diet & foraging habits
• Seedeaters - thick, crushing beak
• Woodpeckers - heavy, blunt, chiseling beak
• Raptors - sharp edged, tearing, hooked beak
• Shorebirds - long, delicate, probing beak
• Mouth - consists of hard upper palate, soft lower palate, distinctive tongue, salivary glands, & taste buds
• Soft palate may be enlarged into a pouch used to temporarily store food, tongue has few muscles in most species

Avian Digestive System

• Crop: expansion of esophagus over the furcula, a storage pouch

Stomach

• Birds: has 2 compartments (glandular & muscular stomach)
• Proventriculus: anterior glandular stomach; chemical digestion begins
• Gizzard: muscular stomach; striated muscles that grind food
• Many birds ingest small pieces of grit aids in grinding food
• Liver: bilobed, right lobe larger than left

Avian

• Pancreas: is large with endocrine and exocrine functions, rests in the loop of the duodenum
• Duodenum: main digestive organ; it varies in length and thickness
• Ceca: paired sacs at junction of small & large intestines, plays role in water reabsorption and bacterial fermentation of cellulose
• Contents are excreted independent of fecal material
• Cloaca: end of digestive tract
• Coprodeum: anterior section which receives excrement from the intestine
• Urodeum: receives discharge from the kidney & genital ducts
• Proctodeum: posterior section; stores the excrement
• Vent: muscular anus

Avian Heart

• Heart: 4 chambers, located in cranial portion of the thoracoabdominal space and enclosed by thin, fluid filled pericardial sac
• Blood Vessels: pectoral & brachial arteries (large), provide blood to flight muscles & wings and renal portal system (the vessels)

Respiratory System

• Erythrocytes: oval-shape, nucleated, percentage of RBC in healthy adult bird 35 - 55%
• Heterophils: equivalent to neutrophils, which have bilobed nucleus
• Rods: Shaped red - orange granules

Oral Cavity: contains

• Trachea: long & coiled
• Syrinx: enlargement of trachea above the lungs, the muscles, air sacs, & vibrating membranes, and this vocalization complexity depends on number of muscles present in syrinx

Lungs

• Mesobronchi in lungs
• No cartilaginous rings divides into secondary bronchi (ventrobronchi)
• Ventrobronchi divide into parabronchi
• Parabronchi connect to air capillaries

More Respiratory Information

• Air Sacs: site of gas exchange, thin walled, lightly vascularized membranes
• Lungs: small, inelastic; air capillaries are at right angles to the blood capillaries and Carbon dioxide continually removed from blood oxygen is continually added
• Air Flow: inspiration is the expansion of thoracoabdominal space and expiration pushes air into the lungs and with the repeated action allows full use of air flow
• Respiratory Rate: varies with species, activity level, age, sex, time of day, & outdoor temperature

Adaptions of the Avian Respiratory System

• Smaller birds typically breathe faster than larger birds, as well as birds in flight having a higher rate relative to nonflying types
• In Thermoregulation. birds can use their breath to increase the amount of heat expelled to aid cooling

Avian System

• Kidneys: located dorsally in slight depression at synsacrum and is elongated with 3 subdivide into lobules with nephrons
• Ureters surrounded by squeezes rate and urine is conveyed through ureters
• Urine composition is nitrogen waste and eliminated a paste with quality feces

Avian Reproductive System

• Reproduction is periodic, increasing daylight stimulates hormone release
• Reproductive organs larger on the left
• Reproductive organs larger on the left

Female Reproductive System Avian

• In females the ovary is rudimentary, reduced gonads decrease in nonbreeding section
• Copulation is achieved in one of two ways and Sperm transfer occurs when the male and female cloaca into cloace proximity
• Oviduct Infundibulum grabs ovum and Magnus secretes alumin

More Avian Reproductive System Details

• Isthmus deposits and Uterus deposits for secretion
• Vagina secretes mucosa, stores for a limited time, lay eggs for one
• Total number eggs clutches
• Determinate Layers specific
• Indeterminate Layers
• The avarian Incubation and eggs
• Average is degree celsicus
• Prolactin promotes breeding

More Chicks Information

• Hormones influence growth.
• They involve powerful egg tools to allow for muscle movement
• Altricial - chicks are skin bare and immobile while some semi have downy coverage or some precocial and Semiattricial feathers