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Avian Flight Muscle and Feather Anatomy and Physiology

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Katelyn O'Connor

on 24 October 2013

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Transcript of Avian Flight Muscle and Feather Anatomy and Physiology

Avian Flight
by Krista Winter and Katelyn O'Connor
Primary Remiges
• The major flight feathers in birds
• Arise from the skin of the manus
• Have an asymmetrical vane
• There are commonly 10 primaries found in birds numbered from the carpus distally.
• some passerine species (eg song birds) possess 9 primaries and other birds such as pelicans (order Pelecanidae) and cormorants exhibit 11
• They provide the main forward thrust in flight.
• Primary feather length can indicate flying style with some exceptions.
• In general larger living birds that soar tend to have longer, pointed wings with relatively shorter primaries (fprim) and longer total arm length (L), whereas smaller birds that are fast flapping flyers are found to have short total arm length, rounded wings and have relatively longer primary feathers.
Primitive ancestor of birds Archaeopteryx is believed to be a soaring bird due to is total arm length and primary feather ratios (although a relatively poor flyer due to other skeletal disadvantages).

Secondary remiges
• They provide the trailing edge of the wing airfoil.
• Arise from the periosteum of the ulna.
• Are asymmetrical in form
• Numbers greatly differ among species from 9 in some passerines to up to 24 in ducks, geese and swans and 25 in larger vultures.

General Feather Structure
Feathers are keratinised epidermis and arise from feather follicles in the dermis. Blood supply is delivered to the feather by the axial artery which regresses after full feather development.

The general structure of an avian feather encompasses the following:

Shaft- hollow longitudinal portion of feather consisting of the calamus and rachis
Calamus – mature end of the feather that is inserted into the feather follicle
Inferior umbilicus – most distal portion of calamus.
Superior umbilicus – at end of the calamus and beginning of rachis
Rachis – long solid portion of the feather shaft
Vane (aka vexillum) – sides of the feather, comprised of barbs which arise from a ramus
Barbs – are arranged into barbules
Barbules – either proximal or distal, are single celled projections off the barbs
Hooklets – found on the distal barbules that hook onto proximal barbules.

For example a pigeons primary feather would have approximately 1000 barbs, and approximately 10,000,000 barbules

Superior umbilicus
Inferior Umbilicus
Bird Flight Aerodynamics
Essentially in order for a bird to fly it must overcome gravity and propel itself forward by generating enough force to do so. The aerodynamics of a bird are extremely complex, but basic aerodynamics of a bird to sustain flight requires enough lift (L) to balance body weight and enough forward thrust to balance backward drag (D).
The relationship between lift (L) and drag (D) can be expressed as:

Where S= area of the wing, p = density of the air, V = velocity of the air stream relative to the wing.
Are lift and drag coefficients that depend on properties of airfoil and Reynolds number, and will not be explained due to extreme complexity.

As drag force opposes the forward motion and acts to reduce the lift. The aerofoil design of the birds is so designed to provide maximum lift and minimum drag.
The air passing over the dorsal aspect of the wing requires longer to travel then the ventral aspect of the wing. This increases the speed, reduces pressure and generates lift (shown in the diagram).
alpha is angle between the surface wing and direction of air stream.
Muscles of

Tail Feathers/ Rectrices
• Are also known as the ‘steering feathers’
• Arise from the pygostyle (last few fused caudal vertebrae)
• Aid in steering the bird in flight in horizontal and vertical plane acting as a rudder and brake.
• Feathers can fan out to increase drag or twist to turn.
• Unlike the primary and secondary remiges are more symmetrical in form
• They are numbered from the centre and then laterally
• Numbers vary among species from as little as 8 in herrons to 24 in ducks, geese and swans.
• Major differences in the tail feather arrangement occurs throughout the avain species. The wedge-tailed eagle exhibits rectrices arranged in a wedged pattern, hence its name.

Ventral Surface of the wing
On the ventral surface of the wing the primary and secondary feathers bases are shielded by adjacent greater coverts of the primary and secondary feathers.
Marginal coverts are also present on the cranial aspect on the wing lining and are arranged in rows.

Function of the coverts
covert feathers are important in providing a smooth passage for air flow over the wing.
Elevation of the coverts are important in slowing the bird for landing.
Mechanoreceptors present on or near the covert feather follicles are said to relay information on the air flow velocity over the wing. Increased covert feather elevation by airstream increases the discharge frequency of mechanoreceptors. This is important information for reducing drag and sustaining flight.

Tail Musculature
Each tail Feather can move individually or as a whole and these complex movements are due to a number of important muscles associated with the tail

1. Levator coccygeus/caudae
O: caudal border of the ilium and the ischium and the transverse process of the last lumbar vertebrae
I: spinous process of the coccygeal vertebrae and the pygostyle
Function: to raise the tail and pull it to side.

6. Lateral coccygeus/ caudalis lateralis :
O: Transverse process of the free caudal vertebrae.
I: on the pygostyle and the rectrices.
Function: to pull down the tail and spread the rectrices.

Coccygeus muscle
O: caudal end of the pubis and ischium
I: outer rectrices, transverse process of coccygeal vertebra and the pygostyle.
Function: pull down tail, pull tail laterally and spread the rectrices

Iliococcygeus muscle
O: dorsal surface of the ilium and dorsal surface of the caudal vertebra
I: outer rectrices
Function: to lift and spread the retrices.

4. Depressor caudae/coccygeus:
O: ventral surface of the of the last sacral and free caudal vertebra
I: ventral surface of the body of the succeeding vertebra and pygostyle.
Function: pull down the tail.

Flight Feathers &

Covert feathers
Dorsal surface of wing
On the dorsal surface of the wing each primary and secondary feather is accompanied by a greater, median and lesser covert.
These are single rows of feathers adjacent to the primary and secondary feathers. The marginal coverts – cover the majority of space of the cranial dorsal aspect of the wing covering the patagium.

Alula Feathers
• Are feathers arising from the alula digit or digit 1 (commonly called bastard wing).
• Usually consist of 3 – 5 feathers.
• The usually position of the alula digit is directly adjacent the second digit and rarely visible in flight.
• The alula digit however can be extended voluntarily and important in both take- off and landing by controlling airflow over the wing.
• The alula digit is said to be somewhat akin to the leading edge of the wings of an aircraft as it works as to decrease the airspeed close to the leading edge and turbulence at the lagging edge, which ultimately reduces stall (loss of lift), at high angles of attack (see diagram).
• Muscles associated with and responsible for movements in the alula digit include adductor digiti I, extensor digiti I and flexor digiti I.

Take The Quiz

1.Which muscle of flight provides the powerful down beat/depression
during bird flight?
a) Sternobrachialis part of the pectoralis
b) Supracoracoideus
c) Deltoid major
d) Biceps Brachii

2.What major flight muscle inserts on the dorsal tubercle of the humerus?
a) Sternobrachialis part of the pectoralis
b) Supracoracoideus
c) Scapulotriceps
d) Humerotriceps

3.What is the main function of the biceps brachii?
a) Flex the elbow, raise the wing
b) Extend the elbow
c) Depress the wing during flight
d) Only raise the wing during flight

4.Which feather group is associated with preventing stall in birds at
high angles of attack?
a) Primary feathers
b) Secondary feathers
c) Alula feathers
d) Tail feathers

5.In bird flight what are the basic aspects in aerodynamics to sustain flight?
a) Increase drag, increase lift
b) Increase lift, decrease drag
c) Increase stall, decrease drag
d) Decrease lift, increase drag

6.What is generally correct for a soaring type bird with respect to total arm and primary feather length?
a) Short total arm length and large primary feather length
b) Long total arm length and shorter primary feather length
c) Short total arm length and shorter primary length
d) Long total arm length and longer primary feather length

Alvarez, J.C, Meseguer, J, Meseguer, E and Perez, A 2001 ‘On the Role of the Alula in the Steady Flight of Birds,’ Ardeola, Vol. 48, pp. 161-173.

Baumel and Witmer, L 1993 ‘Handbook Of avian Anatomy: Nomina Anatomica Avium,’ Publications Of The Nuttall Ornithological Club, No. 23

Brown, R and Fedde, R 1993 ‘Airflow sensors in the Avian Wing’ journal of Experimental Biology, Vol. 179, pp 13-30.

Chitescu. St, Cotofan, V and Hillebrand, A 1976 ‘Atlas De Anatomie A Pasarilor Domestice’, Editura Academiei Republic11 Socialiste Romania

Corvidae E.L., Bierregaard R.O. and Peters S.E. 2006 'Comparison of Wing Morphology in Three Birds of Prey: Correlations With Differences in Flight Behavior,' Journal of Morphology, Vol. 267 pp.612-622

Dhawan, S 1991 ‘Bird Flight’ Sadhand, Vol.16 pp.275-352

Gatesy, S And Dial, K 1992, ‘Tail Muscle Activity Patterns In Walking And Flying Pigeons (Columba Livia),’ Journal Of Experimental Biology.Vol 176, Pp. 55–76.

Hout P.J. Mathot K.J., Maas L.R.M and Piersmaa T. 2010, 'Predator escape tactics in birds: linking ecology and aerodynamics,' Behavioural Ecology Vol. 21, pp.16-25

Marden J.H. 1990, 'Maximum load-lifting and induced power output of Harris' hawks are general functions of flight muscle mass,' Journal of Experimental Biology, Vol. 149, pp.511-514

Nickel, R, Schummer, A and Seiferle, E 1977 Anatomy of the Domestic Birds, Verlag Paul Parey, Berlin and Hamburg.

O’Malley 2005 Chapter 6 Avian anatomy and Physiology Clinical Anatomy and Physiology of Exotic Species

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Peters S.E. and Dobbins C.S. 2012, 'A Comparative Study of the Mechanics of the Pectoralis
Muscle of the Red-Tailed Hawk and the Barred Owl,' Journal of Morphology, Vol. 273, pp.312-323

Proctor, N and Lynch, P 1998 Manual of Ornithology: Avian Structure & Function, Yale University Press.

Scott, W, Stevens, and Binder-Macleod, S 2001 ‘Human Skeletal Muscle Fiber Type Classifications,’ PHYS THER. Vol. 81, pp. 1810-1816.

Wang, X, McGowan, A and Dyke, G 2011 ‘Avian Wing Proportions and Flight Styles: First Step towards Predicting the Flight Modes and Mesozoic Birds journal of evolutionary biology vol. 6,

Wang, X, McGowan, A and Dyke 2011 The primary feather lengths of early birds with respect to avian wing shape evolution,’ Journal of Evolutionary Biology, Vol. 24 pp. 1226–1231

Welch, K and Altshuler 2009 ' Fibre type homogeneity of the flight,' JournaL comparative and physiology, Vol 152, pp324-331
General Anatomy
The main muscles of flight are the
These muscles can collectively represent about
of a bird's body mass!
They provide
stability for flight
, as the heavy musculature (along with the muscular gizzard) is located ventrally, at the
centre of gravity

Another way to categorise avian flight muscles is through:
General Physiology
Muscle physiology Review

Muscle fibres are compiled of repeating functional units called sarcomeres that contain myofibrillar proteins actin (thin filament) and myosin (thick filament). Interactions, in particular binding of these two elements, allow contraction of muscles. Arrival of an action potential at the neuromuscular junction causes ACh relase, and results in transmission of the action potential in the sarcolemma. Upon arrival of calcium ions from the sarcoplasmic reticulum heavy chain regions of the myosin protein bind to the revealed actin binding site, upon calcium ion binding to troponin. The myosin protein also contains an ATP binding site. Hydrolyzation of ATP to ADP by enzyme (adenosinetriphosphatase [ATPase]) provides the necessary energy for muscle contraction. Muscles fibres are divided into slow or fast fibres based on their myosin ATPase activity and the speed of muscle shortening, and therefore contraction. Fibre typing is based on histochemical staining and metabolic enzyme biochemical identification.

Three main muscle fibres have been identified in avian skeletal muscle
which include

• Type I - slow oxidative fibers (FO).
• Type II - fast twitch oxidative-glycolytic (FOG),
• Type II -fast twitch glycolytic (FG)

Avian Muscle Fibre Types

Fast Flapping Birds

The Zebra finch and Hummingbird showed all muscles in the pectoral girdle and wing
to be exclusively fast oxidative glycolytic fibres (FOG).
Other passerine species have found similar results, concluding that fast glycolytic oxidative fibres are best suited for the high contraction frequencies associated with their flight style.

Gliding -Soaring Birds

Albatrosses which are elite gliding birds and considered to be one of the most economical flyers among birds showed slow fibres in the deep pectoral and fast muscle fibres in the superficial pectoral muscle. These slow muscle fibres present in the deep pectoral muscle of many gliding birds are said to support the body between the wings by undertaking isometric contraction, while the superficial pectoral muscle provides the power for take off and when engaged in flapping flight.

Flightless birds
The pectoral muscle of the chicken is 'white' and therefore lacking in myoglobin, as compared to the gastrocnemius muscle which is 'red' due to its high myoglobin content. This suggests that chickens spend more time walking presumably looking for food then engaging in flight.
Differences in Muscle Fibre Types with Flight Style
Now let's look at the specific muscles!
2 heads:
superficial sternobrachialis
Deep thoracobrachialis
They are joined by a
tendinous intramuscular membrane
and have different fibre orientations. The difference in
of the 2 heads varies between species, depending on
flight behaviour

They are supplied by separate primary nerve branches. Activation patterns of the 2 heads are distinct and have
different patterns of EMG intensity
during different behaviours.
origin: keel/sternum, furcula and sternal ribs


origin: lateral surface of sternum and coracoclavicular membrane
insertion: cranial aspect of pectoral crest of the humerus

insertion: lateral tuberosity and lateral tubercle crest of humerus
Function: pronation and protraction of humerus during adduction of wing
Function: slight opposing force to humeral adduction used for landing to control wing
Lies deep to the pectoralis

lifts wing for upstroke
not as necessary while in flight, mainly for takeoff
Origin: Sternum
Insertion: dorsal tubercle of the humerus (after running dorsally through triosseal canal)
Biceps brachii
Origin: near glenoid fossa and proximal head of humerus
For most birds it becomes tendinous and bifurcates
Muscles of

a) Sternobrachialis part of the pectoralis provides the powerful downstroke in flight. The supracoracoideus provides the uplift during flight by raising the humerus. The deltoid muscle flexes shoulder, rotates wing outward to lift the wing and the biceps brachii flexes the elbow.

b) Supracoracoideus. The sternobrachialis inserts on the deltopectoral crest. Both the scapulotriceps and humerotriceps insert on the olecranon of the ulna.

Main insertion: tuberculum bicipitale radii, or a fovea in the higher passeriforms
a) flex the elbow and raise the wing
c) Alula feathers. The primary feathers provide
the main forward thrust in flight. The secondary feathers make up the trailing end of the airfoil and the tail feathers are important in breaking, landing, stearing and take off.

Second insertion: tuberculum bicipitale ulnae (usually)
b) Increase lift, decrease drag.
Sustained flight requires enough lift
and reduced drag. In situations where
drag is increased and lift is lost,
this is termed as stall.
b) Long total arm length and shorter primary feather length. short total arm length and larger
primary feather length is typical of fast flapping
birds e.g. the hummingbird.
Function: flexes wing, which will maintain the balance between left and drag, and change the instantaneous aspect ratio during manoeuvering
Triceps brachii
2 parts: scapulotriceps
and humerotriceps
Origin of scapulotriceps: scapular neck
Origin of humerotriceps: fossa pneumotricipitalis of the proximal humerus
Both insert: onto olecranon of the ulna
Function: extends wing, and flexes shoulder
Tensor propatagialis
Origin: distal coracoid and pectoralis muscle
Insertion: tendons insert on antebrachium and carpus
adjusts shape of leading edge of wing
therefore regulates lift generation and wing camber
may also aid wing flexors
extends carpus and
ligamentum propatagiale
Ligamentum propatagiale:
o is elastic in the centre and collagenous at each end
o from the elastic part, elastic branches protrude and spread across the propatagium to insert on the dorsal antebrachial fascia of the distal ulna
Origin: proximal clavicle, scapula and coracoid
Insertion: deltoid tuberosity of humerus
Function: flexes shoulder, rotates wing outward to lift wing
History snippet
: the Archaeopteryx must have been a poor flier as it had poorly developed pectoralis muscles and no triosseal canal. It is presumed the deltoid muscle provided the primary force for lifting the wing of this ancient bird ancestor.
The University of Adelaide
Veterinary Anatomy and Physiology III
Triosseal canal
The function of an avian muscle can be ascertained by its
A deeper red colour has been attributed to
higher myoglobin
levels and

increased blood supply

within the muscle tissue.
Myoglobin is a hemoprotein which is the primary oxygen-carrying pigment found in striated muscle tissue.
These red muscles use
aerobic metabolism
, needed for long duration activities such as flying.
White-coloured muscle is powered mainly by
anaerobic metabolism
, which causes a lactic acid formation, and only usually allows for short bursts of muscular contractions. Example: This is found in the pectoralis muscle of farmed chickens.
Avian Red Muscle vs. White Muscle
Fast Oxidative Glycolytic (FOG)

FOG fibers are often smaller in size and contain both oxidative and glycolytic enzymes. They may have less force potential but are more fatigue resistant than FG fibers.
Fast Glycolytic Fibres (FG)

Fast glycolytic fibres generate high force, and
have rapid contractile properties. They are used for short burst activities, and relatively sucseptible to fatigue.
Slow Oxidative Fibres (SO)

slow fibers are highly oxidative and fatigue-resistant, but produce relatively low contractile force. These muscles are used in slow repetitive movements and sustained contractions needed in postural muscles.
Shy Albatross
Zebra Finch

NADH tetrazolium Reductase stain
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