Lecture 3.pdf

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Ecology & Evolutionary Biology
Michael Denny

Lecture 3 Avian flight SystemAnatomy Introductionbirds are capable of powered flightcan be defined as the capacity to produce lift accelerate thrust and manoeuvre at various speeds distinct from simple glidingbats arthropods and birds are the only taxas capable of power flightsugar gliders do not use power flightuse tail during gliding to give stabilityFlight Systemstrong but light structureair tight lift surfacemuscle power for thrustwing shape change for manoevrabilityWhat is a featherdead keratinized derivatives of the vertebrate epidermistwo defining characteristics o composed primarily of betakeratin 90 o tubular structure produced in a follicleSkeletal Anatomy of Flight Apparatusbird forelimb has been modified during evolution from the basic tetrapod pentadactyl forelimb of ancestral reptilesthere has been loss of 2 digits in the adult hand shortening of the remaining 3 digits loss of phalanges and lossfusion of carpals and metacarpals into the carpometacarpushand elements are somewhat flattened and fusion makes them robustideal as insertion points for primary flight feathersbats have a heavier skeleton compared to birds and terrestrial animalsPectoral Girdleclosely connected to the wingvery modified in birdsthe girdle consisted of clavicles fused into the furcula wishbone paired coracoids acts as struts supporting the broad flat sternumthe sternum of volant able to fly species has a prominent keel carinathe scapular in birds is usually thin and swept backdoes not provide much muscle attachment notably in penguins where it is quite broadMusclebirds have centered their forelimb power muscles not at the shoulder but instead down under the bodyon the breast close to their centre of gravitythe sternum especially the keel is the main region for power stroke flight muscles the pectoralis and supracoracoideus muscleshummingbirds the sternum particularly the keel comprises a significant proportion of the skeletonflightless birds ex ratites the sternum if flat and there is no carinaneed to pull wings down and raise them2 muscles are needed o muscles work by contractiontotal flight musclebody masspectoralsupracoracoideusbody masspectoralis muscle powers downstroke in birds o largest muscle in birdscan comprise 30 of the body weight o resides on the breast o tendons run up to the dorsal surface enlarged head of the humerus inserting on the deltopectoral crest
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