Chapter   17 - AVES

new day by Teslin Chaney

1. 9,100 species distributed nearly world-wide: More numerous than any other groups of vertebrates except for fish. The single unique feature that distinguishes birds from all other living vertebrates is the presence of feathers.
2. more uniform in characteristics than mammals: partly due to selection for flight

FEATHERS and FLIGHT

1. Origin of Feathers
   1. Feathers: a unique avian character original function probably insulation, later modified for display, then for flight.
   2. Derived from epidermal placodes (Box 17-1): early development of reptile scale & bird feather similar.
   3. Made primarily of beta keratin, as is reptile scale and mammalian hair.
2. two primary functions
   1. insulation - traps air space
      1. birds are endotherms
         1. maintenance of a high body temperature
         2. advantages: increased power and endurance
   2. light-weight air foils for flight
   3. secondary functions: display, sensory, protection
3. basic types of feathers: Pp. 488-491
   1. contour feathers [fig 17-2]
      1. typical feathers: calamus (quill), rachis (shaft), and vane consisting of barbs, proximal and distal barbules (with hooklets)
      2. flight feathers: remiges (wing feathers) and retrices (tail feathers)
      3. typical body feathers [fig 17-2b]
   2. semiplumes [fig 17-4a]: insulation below contour feathers
   3. down feathers: insulation--entirely plumulaceous
   4. bristles [fig 17-4b]: specialized bristles around bill and eyes, may aid in the capture of flying insects (e.g., in nighthawks and flycatchers)
   5. filioplumes [fig 17-4c]: specialized sensory feathers in some birds that may aid in the operation of other feathers.

AERODYNAMICS OF THE AVIAN WING

1. Airfoil (wing) - streamlined in cross section, with a slightly concave (cambered) lower surface; air moving over the top of the wing travels faster than the air beneath the wing, causing lower pressure on the upper side, thus providing lift. [fig 17-8]
2. Wing slot - gaps in between primary wings which direct more rapidly-moving air over the upper surface of the wing to provide more lift. reduce air turbulence which would cause a stall at the high angle of attack needed for slow flight [fig 17-8]
   1. alula [fig 17-6, 17-8] - group of small feathers on the "thumb" of the wing which provides a midwing slot.
   2. slotting between primary feathers at the end of the wing - which provides a wing-tip slot
3. tapered wing reduces drag caused wing tip turbulence (induced drag). long narrow wings have high aspect ratios (L/W) and high lift to drag (L/D) ratios.
4. wing load [table 17.1]
   1. mass/wing area is usually less in smaller birds (lighter wing loading); heavier wing loading is present in powerful fliers (e.g., hummingbirds) versus soarers (swallows).

flight muscles [fig 17-10]

1. pectoralis for the downstroke
2. supracoracoideus (with tendon) for the upstroke (wraps around coracoid and scapula)

Types of bird wings [fig 17-12]

1. Elliptical [fig 17-12b]
   1. short, broad elliptical wings with large wing slots at tips and distinct alula at midwing;
   2. low aspect ratio (ratio of length to width), high camber; birds that must maneuver in forested habitats, such as flycatchers, sparrows, warblers, doves, woodpeckers, and magpies.
2. High aspect ratio [fig 17-12c]
   1. high-speed - long, slender wings with no wing slots and pointed tips; no alula; outer half sweeps back relatively sharply; birds that feed in flight, such as swallows and hummingbirds, or that make long migrations, such as sandpipers and gulls.
3. Dynamic Soaring [fig 17-12a]
   1. long, narrow wings with no wing slots; only slightly sweeping back near outer third of the wing; high-aspect ratio; oceanic soaring birds birds that include albatrosses and frigate birds; suited for high speed, high lift, and dynamic soaring.
   2. possible only when there is a pronounced vertical wind gradient; friction with ocean slows the lower 15 m, constant high winds in the roaring 40's--where most albatrosses and petrels are found
4. High-lift [fig 17-12d]
   1. static soaring: glide in air masses that are re rising faster than they are sinking.
   2. relatively long, broad wings with large wing slots at tips and distinct alula at midwing, and pronounced camber, all of which provide high lift at low speed; many of these birds (vultures, hawks, eagles, and owls) are land soarers that require:
   3. the ability to carry heavy loads (e.g. prey) provided by high-lift aspect
   4. maneuverability over terrestrial habitats (also provided by the broad, slotted wings)
   5. also in storks, pelicans
      

Skeletal Modifications for Flight: [Fig. 17-7]

1. pneumatic bones--thin, hollow bones [Fig. 17-6]
2. feathers may weigh more than skeleton
3. loss of teeth and heavy jaws; replaced by horny beak -- lighter [Fig. 17-18 ]
4. specialization of forearm bones to support flight feathers
5. loss of tail: pygostyle--fused 5 remaining caudal vertebrae; platform for tail feathers.
6. furcula - fused clavicles, only in birds [and theropods]--"wishbone"; provides extra bracing for shoulder girdle
7. synsacrum: fused pelvis and 23+ vertebrae
8. bipedal (walking, hopping, perching) [fig 17-13, 17-16]
   

HEART, LUNGS, GAS EXCHANGE

1. Physiology
   1. birds are endothermic--maintain a constant body temperature--40º C
   2. high metabolic rate--to cope with high energy cost of flight
2. Circulatory System
   1. 4-chambered heart-no shunt
   2. nucleated red blood cells--as in all lower vertebrates
3. Respiratory System Pp. 272-277
   1. well developed lungs, one-way (not tidal) air flow system [Fig. 11-8]
   2. Air sacs connected to lungs [Fig. 11-7]
      1. function to reduce density of bird and to cool the animal, especially from heat generated by muscular activity during flight.
      2. These are well developed in good fliers, they even enter spaces in long bones.
      3. flow of air through avian lungs and air sacs [Fig. 11-8]:
         1. inspiration
            1. to posterior air sacs and parabronchial lung
            2. air from lung to anterior air sacs
         2. expiration
            1. to parabronchial lung from posterior air sacs [Fig. 11-8]
            2. out from anterior air sacs
      4. Because of crosscurrent exchange in lungs, blood leaving the lungs has higher O₂ than exhaled air.
   3. efficiency of lung enables birds to breath at much higher altitudes than mammals [Box 11.1]

CLASS AVES

Avian Systematics: [Figure 16-28; Table 16.1]

Archaeopteryx [figs. 16-22, 16-23, 16-24, 12-25]  (late Jurassic)

• Characteristics
1. flight feathers
2. furcula (fused clavicles) present, as in modern birds
3. expanded sternum absent
4. thecodont teeth
5. long tail without a pygostyle
6. metacarpals separate, not fused--claws on hands
7. hand reduced to 3 digits
8. pubis oriented intermediate between theropod and bird
9. capable of gliding or powered flight as evidenced from the structure of the feathers and the forearm.
10. The postcranial skeleton is predominantly reptilian, the skull shows a combination of primitive avian and archosaurian characters

Ornithothorraces: all other birds.  They are better adapted for powered flight

• Characteristics
  1. pygostyle present;
  2. strutlike coracoid
  3. sternum present

Orser Enantiornithoformes (Cretaceous)

• the predominant land birds of the Cretaceous; teeth and gastralia are present; include forms such as Sinornis [figure 16-26]

Order Hesperornithiformes

• loon-like sea birds of the Cretaceous
• teeth are present
• Hesperornis [Figure 16-27]

Infraclass Neornithes ("New Birds")

Characteristics

loss of teeth

Superorder PALEOGNATHAE (Cenozoic)

• mostly flightless birds; which have a flat sternum with poorly developed pectoral muscles, that live primarily on Southern Continents
• ratites (kiwis, emus, cassowaries, rheas, ostriches, moas) and tinamous

Characters

1. usual absence of flight feathers
2. paleognathous palate (large vomers, small palatines, with pterygoid-vomer articulation
3. sternum reduced, usually without a keel
4. pygostyle poorly developed or absent.

Taxa

1. Aepyornis [fig. 17-14a], the elephantbird of Madagascar, stood around 3 m tall and weighed about 660 kg, 20 lb. egg, 1 ft. long, 2 gallons; herbivore
2. Dinornis, a moa from New Zealand stood 3.6 m tall and weighed up to 300 kg, herbivore.
3. Ostrich: largest living bird; 2.6 m tall; lives in Africa; eats plants and small animals; ostrich up to 150 kg
4. Emu: lives in Australia and reaches 6'
5. Cassowary: lives in Australia & New Guinea
6. Kiwi: 3 species that live in New Zealand
7. Rhea: South America
8. Tinamous: only group of ratites that fly, found in South America, Central America, and Mexico
   

Superorder NEOGNATHAE (Cenozoic)

Characters

1. all other living birds Table 16.1
2. carinates - the flying birds that have a keeled sternum on which the powerful flight muscles insert. Some carinates have become flightless
3. neognathous palate  (small vomers, large palatines, pterygoid not reaching vomer articulation)
4. About 22 orders, including the following:

1. Order Podicipediformes: grebes;
2. Order Anseriformes: waterfowl
   1. including ducks, geese, and swans:
   2. Trumpeter swan is the heaviest flying bird: trumpeter swan--17 kg;
3. Order Pelicaniformes: marine birds;
   1. including pelicans, cormorants, anhingas
4. Order Ciconiiformes: wading birds
   1. egrets, herons, ibises, spoon bills, and storks:
   2. New World vultures are probably closely related to storks
      1. The largest flying bird was the extinct giant condor, Argentavis, a Teratornithidae (related to New World vultures) from the late Miocene of Argentina, that weighed 75 kg, stood 2 m tall and had a wingspan of up to 8 m.
5. Order Falconiformes: birds of prey;
   1. including  hawks, eagles, falcons and Old World vultures
6. Order Galliformes: fowl; including the chicken, turkey, grouse, and pheasants:
7. Order Gruiformes:
   1. 12 families, including cranes, coots, rails
   2. terror cranes: extinct, flightless, giant (over 2 m tall), cursorial predators   evolved independently at least twice in the Gruiformes
      1. Diatryma: [Paleocene and Eocene of North America and Europe]
      2. Phorusrhacus [Miocene and Pliocene of South America] and Titanis [Pliocene and Pleistocene of North America]
8. Order Charadriiformes: shorebirds; including plovers, sandpipers, gulls, terns, and skimmers:
9. Order Gaviiformes: loons;
10. Order Columbiformes: including pigeons, doves, and the recently extinct dodo:
11. Order Psittaciformes: parrots and macaws;
12. Order Strigiformes: owls;
13. Order Apodiformes: hummingbirds and swifts;
14. Order Piciformes: woodpeckers and toucans;
15. Order Passeriformes: perching birds/songbirds;
    1. 84 families
    2. comprise over 1/2 (more than 5000 species) of all species of birds,

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