1. Recall: Lift As a fish or a bird moves through the water fins/wings create lift forces -- forces that tend to raise or lower the animal. These forces “originate from [fluid] viscosity and are caused by asymmetries in the flow. As fluid moves past an object [such as a fin or a wing], the pattern of flow may be such that the pressure on one …side is greater than on the opposite. Lift is then exerted on the object in a direction perpendicularto the flow direction” (Sfakiotakis 1999). Lift decreases, drag increases with increasing tilt of hydrofoil or aerofoil relative to the direction of flow.

2. Hydrofoils and aerofoils: the fluid flowing faster has lower pressure; faster flow occurs on the upper surface of an aerofoil or hydrofoil and so lower pressure generates lift. Hydrofoils more robust than aerofoils: due to fluid density; water is more dense than air Linden Gledhill Harris’ Hawk Ladybird beetle Diversity in aerofoil shape Animal wings must not just generate lift they need to move through a cycle of propulsion: bird flight involves dips, cardinal.

3. Some wings don’t look like aerofoils

4. Feathers are themselves aerofoils Rachis: tapering central support of a feather: to either side is the vane Body feathers have vanes symmetrical about the rachis, but bird primaries are not symmetrical in this way: in primaries the rachis is closer to the edge that leads in flight. In strong fliers the leading primary vane is sometimes almost obliterated. This asymmetry gives each feather an aerofoil transverse section, i.e., the primaries of most birds function as aerofoils in their own right. Feduccia, A. & Tordoff, H.B. 1979. Feathers of Archaeopteryx: asymmetric vanes indicate aerodynamic function. Science 203: 1021-1022 Primary feathers

5. * [ mod. from Wikki] Keratin a fibrous structural protein. Keratin is the key material in the outer layer of human skin; also in hair, nails and bird feathers. Keratin monomers assemble into bundles to form intermediate filaments, which are tough and insoluble…. The only other [material] known to approximate the toughness of keratinized tissue is [the polysaccharide] chitin.

6. Figure 4. The structure of the trailing edge vane of a pigeon primary feather. The barbs are inclined from the vertical and cambered in cross section and the proximal barbules curve near their tip. This structure facilitates distal and ventral movement of the blade (arrows) and helps prevent proximal movement and detachment of the barbules. Distance between barbs is approximately 0.5mm Katayoon Taghizade et al. Designing a Mobile Facade Using Bionic Approach. American Journal of Materials Engineering and Technology, 2013, Vol. 1, No. 2, 22-29. doi:10.12691/materials-1-2-2 © The Author(s) 2013. Published by Science and Education Publishing.

7. Another function of feathers besides promoting smooth flow of air and lift: thermal insulation Thermal insultation: reduction of heat transfer between objects of differing temperature. ‘Low thermal conductivity materials reduce heat fluxes’. Gases are poor thermal conductors compared to solids and liquids Trapping air in small surface pockets that stop transfer of heat by natural convection. Birds in winter: fluffed at the bird feeder. Riding a bike at low temperatures without gloves is not a good idea. Wind- chill will soon make your hands uncomfortable. Flying makes low temperatures a larger problem and the feathers are an adaptation for this. Taghizade K. & Taraz M. 2013. Designing a mobile facade using bionic approach. Doi: 10.12691/materials-1-2-2 Feathers as insulators; feather movements on the skin – puffing out or sleeking down…bionics “explains the relation between nature and product design” “innovative designing and engineering based on the systems present in nature” outside of buildings “This arrangement produces a light structure which …may be easily mended by the bird drawing the vane through its bill.”

8. Load of wing is taken up by the tendon of the supracoracoideus. Stress (force) is created by the contracting muscle and tension develops in the tendon which stretches, i.e., shows strain. Supracoracoideus muscle is wing elevator; it originates on the sternum and lies beneath its antagonist, the wing levator. Direction of muscle pull is changed by the rope-like nature of the tendon, i.e., it is a pulley.

9. Why are the muscles that power bird flight located below the wing? Flight muscles are 1/5 of the body mass. Keeping the centre of gravity low keeps the bird from out-of-control rolling.

10. Class 3 lever both up and down: effort is always applied between the fulcrum and the load in birds.

11. Costal suction pump Intercostal muscles run between ribs and contract to move ribs forward and downward during inspiration; this coincides with downstroke: sternum moves forward and down. Forward and down the volume of thoracic cavity is greatly increased giving reduced internal pressure and causing an air inrush. Reverse happens on upstroke. Sternum moved down (and up) by supracoracoideus and pectoralis major operating during flight: flight power movement integrated with ventilation.

12. Lungs of human occupy about 5% body volume. Lungs of bird only occupy 2% of body volume. But lungs plus air sacs of a duck occupy about 20% of its body volume. Nevertheless bird air sacs are not involved in gas exchange: they are not vacularized (no blood vessels): but they are involved in air circulation. Air sacs are reconnected to the mesobronchi by recurrent bronchi. Multiple functions of air sacs: cooling system: flying produces heat and air sacs are well placed to remove this excess heat (bird has an air-cooled engine). Shock absorber: gannets, pelicans diving into the ocean from a great height. Resonance: sound box areas in bird sound production. Egg laying: abdominal air sacs help in egg laying (and in defecation?). Birds have pneumatic bones (air-filled) and air sacs

13. Tiny air capillaries within the parabronchi walls, in the (fixed-volume) lungs, are the site of actual gas exchange. Bird lung section Tracheae, which conduct the low density fluid (air) into the body need cartilaginous rings to support their lumen against the denser tissues (water- based) that surround. Convergence of a sort with the tracheae of insects.

14. Syrinx is located at junction of trachea and bronchi and is an organ for sound generation: developed elaborately in songbirds. Modulation of air flow to create sounds: respiratory system serves also in communication. There are 9 air sacs. An anterior group: interclavicular (1), cervical (2), anterior thoracic (2). Then there is a posterior group: abdominal (2), posterior thoracic (2). Unpaired interclavicular air sac in anterior midline sends diverticulae into some of larger bones (sternum, pectoral girdle): called pneumatic bones: these serve to lighten the bird for flight. Bird air sacs are how a bird can inhale and exhale with lungs that don’t change volume. Posterior thoracic sac

15. Diagram to right is simplified bird lung, ‘it ‘groups’ anterior and posterior air sacs in order to more easily visualize the air circulation. The lungs cannot change their volume, but the air- sacs do. Two cycles of inspiration and expiration (powered by the muscles of flight, including the intercostal muscles between the ribs of the thorax) are required for one breath to make its way through the system, in and out again; it is a true circulation and not a tidal system such as in mammals.

16. Follow one breath through the system: remember, on inhalations sacs expand, on exhalations they are compressed, this being accomplished by thoracic volume changes linked to flight muscles & rib cage [costal pump]. Inhalation 1, posterior air sacs expand & draw breath into themselves: draw this air via primary bronchus>mesobronchus. Exhalation 1, breath air displaced from squeezed posterior air sacs into posterior secondary bronchi and parabronchi; in latter the gas exchange occurs. Inhalation 2, expanding anterior air sacs draw ‘breath’ from the parabronchi into themselves. Exhalation 3, the anterior air sacs expel the air breath to the outside.

17. ‘Ontogenetic transitional wing hypothesis’ of how birds evolved flight. To select forelimbs for flight -- to alter the neuromuscular system and forelimb form to create a powering aerofoil -- involves many complex body changes. A ‘protobird’ ancestor had to change gradually from a ground-walking reptile to a bird capable of “level flapping flight” (i.e., from a lizard to a soaring eagle). Needed is a plausible hypothesis of locomotion-related selection pressures: one that envisages gradual changes to forelimbs that are adaptive throughout the evolutionary process, i.e., are adaptive at each stage in the historical process. The authors of a recent paper propose an hypothesis based upon study of the development (ontogeny) of young partridge, the ontogenetic-transitional wing hypothesis. They studied ‘wing-stroke dynamics’ of maturing partridges and traced a developmental pattern of forelimb movement that is consistent with ‘incline flap running’. Dial, K.P. et al. 2008. Nature. A fundamental avian wing-stroke provides a new perspective on the evolution of flight. Nature 451: 985-989. Read this paper to understand their hypothesis, how they arrived at it and what experimental evidence they present that tests the hypothesis. “…we propose that explorations of the ontogeny of post-natal behaviour and morphology among extant taxa provide insight into ecological and evolutionary locomotor transitional stages” (jargon destroys interest)

18. Chukar: Alectoris chukar Backyard chickens As newly hatched young birds move about, they use their developing wings as well as their legs. The wingstroke goes through changes as young bird matures. The ontogeny of wing movement ‘recapitulates’ phylogenetic change. The wingstroke referenced to gravity rather than the longitudinal axis of the bird is very conservative and useful at each stage.

19. “Our data suggest a default or basal wing-stroke is used by young and adults and may exist in all birds…. At hatching, chicks can ascend inclines as steep as 60° by crawling on all four limbs. From day 8 through adulthood, birds use a consistently orientated stroke-plane angle over all substrate inclines during wing- assisted incline running (red arcs) as well as during descending and level flight (blue arcs). Estimated force orientations from this conserved wing-stroke are limited to a narrow wedge (see Fig. 3b).

20. “Blue and black outlines represent the positions of the bird and wing at the start and end of downstroke, respectively. a, In the vertebral space, the mean wing-stroke plane angle shifts more than 30° from a more antero-posterior orientation during flap-running to dorso-ventrally in flight, implying different wing-strokes are used to execute different locomotor modes. The wing-stroke path is consistently oriented, however, in both the (b) global and (c) gravitational coordinate spaces over diverse locomotor behaviours, illustrating a simplified wing-stroke that is multi-functional. Data for juveniles are presented from 8- to 10-day olds.” When the wing movement is considered relative to the body’s longitudinal axis it seems to vary a lot for locomotory learning behaviour, but considered relative to gravity it is actually the same relatively simple wingstroke for both up-incline and fluttering down incline.

21. “a, When wing-stroke plane angles are viewed side-by-side in both the vertebral and gravitational frames of reference, the wing- stroke is nearly invariant relative to gravity whereas the body axis re-orients among different modes of locomotion. Red lines represent the wing-tip trace in WAIR (flap- running) and blue lines represent the wing-tip trace in level flight. b, Wing-strokes are estimated to produce similar aerodynamic forces oriented about 40° above the horizon during WAIR, level flight and descending flight. Error bars are s.e.m. c, Representative traces of AOA through a wing-beat for an animal flap-running vertically (red) and in horizontal flight (blue) demonstrate the similarities of AOA among behaviours. The similarities are further clarified by examining wing cross-sections and mean global stroke-planes in the first, middle and last thirds of downstroke. Here, the orientation of the aerodynamic force (F aero ) is estimated from the middle third.”

22. Conclusions about flight evolution “Our experimental observations show that proto-wings moving through a stereotypic and conserved wing-stroke have immediate aerodynamic function, and that transitioning to powered flapping flight is limited by the relative size of the wing and muscle power, rather than development of a complex repertoire of wing-beat kinematics.” In other words, wingstrokes were useful to protobirds even before they could take to the air. Wing beats (at the particular narrow range of angles the authors discovered) could help a non-flying bird ancestor to run faster, up or down inclines – faster than ‘birds’ that were not modifying and using their forelimbs in this way. Flapping with forelimbs and running on hindlimbs was a better, faster means of escape from a predator than running on all four limbs at the same time.

23. Turning now to flight in insects: some anatomy is necessary: tergum, sternum, pleuron are ‘top’ ‘side’ and ‘bottom’ of each insect cuticular metamere. Insects are descended from metameric, i.e., segmented animals and the thorax is a locomotory tagma comprised of three metameres. Segments of the abdomen contrast with those of the thorax. The thorax is a tagma functioning as a locomotory ‘box’, giving a firm base on which muscles can originate and pull, muscles for walking (legs below) and for flying (wings above). The mesothorax + metathorax: the two segments specialized for bearing the wings and for flight are together called the pterothorax. Muscles involved in flight in insects (with exceptions, e.g., in Odonata) insert on the exoskeleton of the thoracic box and NOT on the wings directly; they move the wings by distorting pterothorax shape and are referred to as indirect flight muscles. LONGITUDINALS DOWNSTROKE; TERGOSTERNALS UPSTROKE Attitude of the wings (pronation, supination) is achieved by the elastic interplay of the veins and membranes with the air flow. The wings don’t just go up and down and maintain elevation they must scull through the fluid (air) just like fish fins.

24. Locust flight {Source: R.E. Snodgrass The thoracic mechanism of a grasshopper, and its antecedents. Smithsonian Miscellaneous Collections 82, pp. 111. } [This reference is given just for completeness; it is not something you should try to obtain and read, but it is the source of much of the information given here and in the lab.] Locusts are strong fliers. The flight-powering muscles of the locust are indirect and have their effect upon the wings by distorting the pterothorax and by tergal tipping of the second axillary. (The pterothorax is the flight tagma (just segments 2 & 3, not the prothorax.) There are two antagonistic muscle sets: longitudinals (downstroke), and tergosternals (upstroke). contraction of the longitudinals wings go down contraction of the tergosternals wings go up

25. Sct 2 is the scutum of the second segment of the thorax; scutum is a region of the ‘top’ sclerite (tergum) as is Scl 2 which is a tergal region called the scutellum. Muscle 81 is an indirect longitudinal flight muscle pulling between phragma 1 and 2; 112 is another, pulling between phragma 2 not labelled, and 3Ph, pharagma 3). These increase the arching of their respective terga, creating forces at the wing bases (PWP & 2 nd axillary sclerite, see next slide). The longitudinals are situated high up in the pterothorax. Partially obscured behind them, arrayed against the pleuron, are the many tergosternals (83, 84, 89 etc.), running between the sterna (S2,S3) and the terga (Sct2, Sct3). The axes of the tergosternals all lean headward (the insect’s anterior is to the left). Notice how the upper end of the tergosternals insert on the terga where their contraction can reduce the convexity of this region. Reducing tergal convexity is associated with elevation of the wings. Apodemes are Inflections of cuticle, phragma are a kind of apodeme.

26. More diagramatic views: Snodgrass drew the phragmata (Aph anterior phragma, Pph posterior phragma) of Fig. 129 purposely distorted, so as to show their interconnecting longitudinal muscles both ahead and behind: notice the critical placing of the second axillary, 2Ax, atop the pleural wing process, WP.

27. “The addition of flanges stabilizes against buckling since it increases the effective thickness of the plate in selected areas effectively dividing the plate into shorter lengths.” Euler buckling dorsal ventral Function of the pleural ridge Tergosternals contract and forces would tend to buckle the pleuron; the pleural ridge stiffens the side between the wing base and the coxa.

28. Function of the pleurosternal muscles: even more stiffness Imparted to the thoracic sides (pleura): and VARIABLE.