The Insatiable Appetite Costs and Benefits of the High Metabolic Rate of Birds

I. Physiology = metabolism & excretion High body temperature - ca. 40 o C (104 o F) 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 CO 2 ) specifics - nerve impulses travel faster muscles are stronger but birds need 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 - Migration Having 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 System Transports O 2 and glucose & fatty acids (fuel) removes CO 2 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 % 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 bpm lower than some mammals output higher heart larger stroke more efficient ventricle empties more has more, thinner fibers more mitochondria Cost: very high blood pressure!

Metabolism High rates much heat produced Temperature regulation TNZ ca (64-90s) LCZ lower critical zone/UCZ upper critical zone

Metabolism High rates much heat produced Temperature regulation TNZ ca (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 H loss = (T basal – T ambient )/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

“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 Economy Loss through evaporative cooling - especially important in arid regions Brown Towhee evaporative H 2 0 loss quadruples when ambient temp goes from 30 to 40 o C Replaced how?

Swordfish/Tuna Counter-current mechanisms Fish gills

Controlled hypothermia: Hummingbirds, vultures, goatsuckers

I. Water Economy Loss through evaporative cooling - especially important in arid regions Brown Towhee evaporative H 2 0 loss quadruples when ambient temp goes from 30 to 40 o C Replaced how? Drinking 6O 2 + C 6 H 12 O 6 -> 6CO 2 +6H 2 O (high metabolic rate of birds results in more metabolic water than comparable mammals) food - fruit, prey - Sooty Falcons nest where temp in shade is 49 O C (120 o F)

I. Water Economy Loss through evaporative cooling - especially important in arid regions Brown Towhee evaporative H 2 0 loss quadruples when ambient temp goes from 30 to 40 o C Replaced how? Drinking 6O 2 + C 6 H 12 O 6 -> 6CO 2 +6H 2 O (high metabolic rate of birds results in more metabolic water than comparable mammals) food - fruit, prey - Sooty Falcons nest where temp in shade is 49 O C (120 o F) 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 H mammals use 20 times the H 2 0 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 – 2 thoracic – 4 abdominal –2 interclavicular – 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 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 time Varies with wing shape, flight type—examples? Egg production, etc.