Birds – Part II

VERTEBRATE ZOOLOGY (VZ Lecture24 – Spring 2012 Althoff - reference PJH Chapters 16-17)

Bill Horn

Body Form and Skeleton

• Feathers: molded for aerodynamic forces; light, strong…very resilient for their weight

• Skeleton: a) skull is remarkably light b) wing bones air filled c) leg bones heavier than

same-sized mammal *overall:

more mass is concentrated in____________ than comparable sized

mammals

Body organ “reductions”

• Birds ______ urinary bladders

• Most birds have only one ovary (or only one _______________ ovary)

• _________ of both sexes are usually small (with hypertrophy or regression depending on time of year)

Muscle & Cardiovascular Output

• Pectoral muscles (major wing muscles-downstroke) may account for ______ of total body mass of strong fliers

--power output per unit of mass for dove estimated to be 10-20x

that of most mammalia muscles• _______ heart and high rates of blood flow coupled

with complex lungs that a) maximize gas exchange

b) dissipate heat produced by high levels of muscular activity during flight

FAVEOLARLUNG

Streamlining

• Birds _____ vertebrates that move fast enough for wind resistance and streamlining to be important

• “Fast birds”songbirds: up to 50 km per hour

ducks & geese: up to 80-90 km per hour peregrine falcon: 200 km per hour in dive

Structural characteristics like fast-flying aircraft: ______________ make smooth joints between wings and body, and head and body ___________ close to body in flight

Not-so-streamlined

• Some birds are slow fliers….slow to launch into flight, slow in-flight

• “Slow birds”spoonbills

flamingosherons

cranes Structural characteristics opposite of fast-flying

aircraft: long-legged with legs that trail behind and/or

not tucked up under the body long-necks extended

Air-filled bones…fused and thinner bones

• Also referred to as ____________ bones• Not present in all birds• Better developed in larger birds than smaller birds• Diving birds (penguins, grebes, and loons) have

little pneumaticity in their bones• Skeletons of most birds exhibit some pneumaticity

in pectoral girdle and humerous• Pelvic girdle: elongated with ischium and ilium

broader and much thinner than ancestral reptile line….and combined with the synsacrum—a fusion of 10-23 vertebrate…. pygostyle—fused caudal vertebrate

Fusion of vertebrae means more rigidity

• Overall, reduction in number of vertebrae and fusion of vertebrae…and relatively immobile thoraic vertebrae…in combination with elongated, “roof-like” pelvis produce a nearly RIGID vertebral column.

• The rigid “trunk” is balanced on the legs• Femur projects to the anterior…combined with

articulation of with the tibiotarsus and fibula results in this being the bird’s center of gravity

center

of

gravity

Other “skeleton” features of note….• Wings positioned above the center of gravity• Sternum greatly enlarged (most with keels…as

noted) for greater amount of surface area• Scapula extends posteriorly above ribs and is

supported by coracoid which is fused ventrally to the sternum

• Clavicles project to anterior—usually fused to form the furcula (wishbone)… provides additional bracing

• Hind foot typically greatly elongated with ankle joing within the tarsals

• Tarsometatarsusmetatarsals of some toes fused with the distal tarsals

• Tibiotarsustibia fused with proximal tarsal bones

Muscles – Mass distribution differences

• Hummingbirds & swallows

mostly flight

• Predatory birds flight but use

legs to capture prey

• Swimming birds

• “Terrestrial” birds--run

instead of fly to flee

flight muscles ________ of

total body mass, legs _____

flight muscles ~_____ of

total body mass, leg _____

limb & flight muscles about

equal percentage, overall

_______ of total body mass

limb muscle mass ___ than

flight muscle mass

Muscles • Two basic processes “fuel” muscle contract:

a) ____________ metabolic pathways--achieve “quick” response --does not requires O2 --more fast-twitch muscle fibers, relative

to slow-twitch muscle fibersb) ___________ metabolic pathways

--achieve “sustained” response--requires O2 --more slow-twitch muscle fibers, relative

to fast-twitch muscle fibers--slow-twitch muscle fibers contain lots of

_____________

Fast vs. Slow Twitch Muscle Fibers

Category Slow-Twitch Fast-Twitch_____________ more fewer_____________ more lessMyoglobin more lessColor appearance red-brown white____________ build-up lower higherFatigue slower quicker

Muscles & Birds Other “flier” vs. “runner” differences

• Composition of leg muscles indicates regular, sustainable activity

• Composition of breast muscles (major muscle groups responsible for up- and downstroke of wings) indicative to long vs. short flight capabilities

• Fliers—(think songbirds, waterfowl, etc.) a) legs: large amounts of myoglobin b) breast: large amounts of myoglobin

• Runners—(think quail, pheasant, wild turkey)a) legs: large amounts of myoglobin

b) breast: essentially lack myoglobin

Major Flight Muscles

↓ __________________ – origin on keel of sternum (lateral side) and inserts at humerus on

ventral sidecontracts for ______________relaxes during upstroke

↑ _________________ – origin on keel of sternum (lateral side), passes through foramen

triosseum, inserts (tendon) on dorsal head of humerus. Foramen trosseum formed by articulation of the furcula, coracoid, and

scapula.relaxes during downstrokecontracts for ______________

pectoralis

supracoracoideus

__________________

right humerus

Left humerusForamen

triosseum

Major Feather Types on the Wing

Primaries (remiges = wing feathers)

Secondaries (remiges = wing feathers)

Major coverts – leading edge of wing

Alula—forms wing slot on leading edge (at carpal bones

Major Feather Types on the Wing

Fig. 17-8 p444, PJH