the insatiable appetite costs and benefits of the high metabolic rate of birds

The Insatiable Appetite

Costs and Benefits of the High Metabolic Rate of Birds

I.         Physiology = metabolism & excretion High body temperature - ca. 40oC (104oF)

maintained by production of metabolic heat = endothermy permits use of cold habitats/climates provides power and endurance needed for flight requires advanced systems of

heat conservation heat loss water economy (evaporative cooling and excretion) respiration & circulation waste removal (especially N and CO2)

specifics - nerve impulses travel faster muscles are stronger but birds need 20-30 x as much energy as similar sized reptile on fine line where proteins are being denatured

Next lectures will cover a bit of physiology – how do you keep an engine running at such high RPMs? And then seque into the annual cycle of birds. Because resources are not available at constant levels throughout the year (day length changes, winter, dry & wet seasons in the tropics, etc.), and because they have such insatiable appetites, birds have scheduling conflicts.

 “The Primary Directive”:Reproduce and survive to reproduce again.Survival requires:

Eat (and don’t be eaten)Eating requires:

Being where there’s food - MigrationHaving feathers - Molt

• Respiratiory system• components

nostrils (nares) & nasal chamber (rete mirabile)

• trachea (syrinx)• lungs• air sacs (display in Frigatebirds)

The trick - flow-through lungs

• mammals and herps have dead-end, always dead air

• birds replace virtually all air in lungs with each breath

• air intake by sternum

• lower sternum, fill posterior air sacs

• raise sternum, force air into lungs

The Circulatory SystemTransports O2 and glucose & fatty acids (fuel)

removes CO2 and other metabolic waste products

The heart four-chambered (like mammals)

reptiles have 3-chambered-but alligators have 4-chambered oxygenated blood from lungs

->right atrium/ventricle systemic blood from system

left atrium/ventricle to lungs 50-100% larger than comparable mammals

output large proportion goes to legs

more than pectoral muscles! - heat loss? legs & brain get 10-20% of cardiac output heat loss and conservation through rete

resting rate 150-300 bpm lower than some mammals output higher

heart larger stroke

more efficientventricle empties morehas more, thinner fibers more mitochondria

Cost: very high blood pressure!

Metabolism High rates much heat produced

Temperature regulation TNZ ca. 18-35 (64-90s) LCZ lower critical zone/UCZ upper critical zone

•MetabolismHigh rates

much heat producedTemperature regulation

TNZ ca. 18-35 (64-90s)LCZ lower critical zone shiver

can’t metabolize brown adipose tissue as mammals do seek microclimate evergreens burrow in snow cavities (often huddle in groups) UCZ – upper critical zone gular flutter panting - evaporative water loss controlled hyperthermia

reduces heat loss by decreasing gradient btn body and environment.

saves water (less lost in evaporative cooling benefits of running body at higher temperatures

(muscles, nerves)

Why does controlled hyperthermia work?

Insulation & Heat Loss  Hloss = (Tbasal – Tambient)/I

 How can a bird manipulate this equation?  Behavior (short & long term)

Structurally (longer term) through molting

Poor insulation = higher metabolic rate

Happy Birthday, Charles!

• Ornithology Today:Evolution -- both its very existence (Archaeopteryx lithographica) and its processes - Darwin and Peter & Rosemary Grant’s studies of Galapagos finches

• Ornithology Today:Evolution -- both its very existence (Archaeopteryx lithographica) and its processes - Darwin and Peter & Rosemary Grant’s studies of Galapagos finches

“There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

The last sentence in On The Origin of Species.

I.         Water EconomyLoss through evaporative cooling - especially important in arid regions

Brown Towhee evaporative H20 loss quadruples when ambient

temp goes from 30 to 40oCReplaced how?

Swordfish/Tuna

Counter-current mechanisms

Fish gills

Controlled hypothermia:Hummingbirds, vultures, goatsuckers

I.         Water EconomyLoss through evaporative cooling - especially important in arid regions

Brown Towhee evaporative H20 loss quadruples when ambient

temp goes from 30 to 40oCReplaced how?

Drinking6O2 + C6H12O6 -> 6CO2 +6H2O (high metabolic rate of birds

results in more metabolic water than comparable mammals)food - fruit, prey - Sooty Falcons nest where temp in shade is 49OC (120oF)

I.         Water EconomyLoss through evaporative cooling - especially important in arid regions

Brown Towhee evaporative H20 loss quadruples when ambient

temp goes from 30 to 40oCReplaced how?

Drinking6O2 + C6H12O6 -> 6CO2 +6H2O (high metabolic rate of birds

results in more metabolic water than comparable mammals)food - fruit, prey - Sooty Falcons nest where temp in shade is 49OC (120oF)

Reduce loss by countercurrent mech. in nasal chambers excrete uric acid instead of urea

molecule of uric acid has 2xs the N as one of urea insoluble, flushed out with less H20 - mammals use 20 times the H20 than birds do to excrete

the same amount of N

Kidneys different - short loops of Henle, so excretion of electrolytes (salts) is not as efficient.

Salt glands located above eyes, drain into nasal passage widespread in non-passerines that have salty diets (mostly marine) - examples? absent in passerines - not clear why. enzymatically run (therefore energetically expensive) may increase resting metabolism by 7%

• Salt Gland

Avian Physiology – Continued & details Air sacs

9 in most birds (12 in some):cervical – 2thoracic – 4abdominal –2interclavicular – 1

extends into bones (humerus & sternum)contacts syrinx,

essential in sound production, heat loss, and cushion internal organs Furcula – spring-like action helps with movement of sternum & hence air flow. Retes – nasal cavities have a “temporal” countercurrent as well as a vesicular one.

Metabolic Rates BMR = Basal metabolic rate—yardstick against which cost of activities can be measured. Resting, in TNZ

Activity Metabolism 

BMR is rare—almost any activity (slight movements, digestion, etc.) raises metabolic rate above BMR

Small birds 10-25 times BMR for hours (mammals only 5-10)Flight is very expensive, but efficient – compare to mammals

Higher per unit time, but you go farther per unit timeVaries with wing shape, flight type—examples?Egg production, etc.